Our crank was balanced at Gressman Powersports. Scott Gressman handled the job using his Sunnen Pro-Bal balancer.
We began by first weighing all components (pistons, pins, locks, rings, bearings, rods). The Diamond pistons required no correction at all, with the entire set weighing in at 542 grams, +/- 0.5 grams). The Lunati rods, though initially matched to within 0.5 grams, now checked out at an average of 619.5 on the big ends (894.0 g total weight), +/- 1.5 grams, due to our shaving the big-end shoulders for cam and block clearance. Definitely close enough, with no need to fiddle with more lightening on even the heaviest rod.
Once Gressman set up his bobweights, he mounted the crank to his Sunnen Pro-Bal stand and positioned each bobweight on-center at each rod journal. Instead of wasting time measuring the bobweight centering location, Scott saves time by using an in-shop-made spacer that drops over the journal between the bobweight and cheek. With the spacer in place, he simply slides the bobweight against the spacer and tightens the bobweight in place. Cool idea.
Our Lunati crank spun up beautifully, with no need for correction in the front at all. In the rear, the crank wanted a bit of added weight in the rear counterweight. Of course, the desired position was shrouded by the rear flange, so Scott secured the crank (upright) on his Bridgeport and drilled through the flange and into the counterweight, followed by adding a 1″ diameter tungsten slug into each hole (flange and counterweight). The horizontally mounted slugs are preferred as opposed to slugs installed at the counterweight perimeters for obvious reasons…no worries about centrifugal force slinging a chunk of heavy metal. After re-spinning the crank, Scott fine-tuned by shaving a bit of weight (about 10 grams) from the shoulder of the rear counterweight using a die grinder. Our final balance was within 0.08 g, which is tighter than needed, so after a quick journal polish, we were good to go.


The Diamond pistons feature 0.990″ pins for a full-float fit to both pistons and rod small ends. Two spiral locks are required at each pin end (four total per piston). As far as piston orientation is concerned, the larger pocket cuts align to the intake valves, so all right-side pistons are oriented with the intake pockets facing the front of the block and all left-side pistons with intake pockets facing the rear of the block. This places all intake pockets in the upper location relative to the block decks. I’m in the habit of using Foster Tool’s way-cool spiral lock installer tools, but when I realized that I didn’t have a 0.990″ tool handy for our pin bores, I wimped out and asked Scott to hang the pistons for me (I’m embarrassed to admit that I just don’t have the technique to install spiral locks with my fingers).

Of course, Scott slipped them in, gave ‘em a twirl and a tap with his fingertip and secured them in place in a heartbeat.


Our block and crank requires the use of a 2-piece rear main seal, so I opted for a Victor seal kit. The seal was installed in the block saddle and rear cap, with a small dab of RTV at the mating surfaces.
With the coated Clevite upper main bearings installed to the block saddles and the lower bearings to the caps, all exposed bearing surfaces were coated with Royal Purple Max-Tuff assembly lube (super slippery stuff that sticks and doesn’t drip out).
The center 1/2″ main cap bolts were snugged first, followed by tightening the outboard bolts (caps No. 2, 3 and 4 feature splayed locations). I addressed the center cap (No. 3) first, followed by No. 2, No. 4, No. 1, and then No. 5. All bolts were initially snugged to 20 ft-lbs, followed by 40 ft-lbs, then 70 ft-lbs and to a final 100 ft-lbs. Crank rotation was observed following each tightening step, with the crank rotating with an applied force of about 1.5 ft-lbs once all caps were fully clamped (not bad, considering the new 2-piece rear main seal).
Crankshaft endplay was measured at 0.007″ (spec is 0.006″-0.008″). By the way, this is a good time to mention how impressed I was with the quality of Lunati’s crank and rods. The crank measured out exactly at spec, with no deviations at all. Each main and rod journal was ground exactly to spec, no taper was found at any journal location, the fillets were executed perfectly, the crank showed no runout, and endplay was exactly at 0.007″. Same with the rods…bore sizing was dead-on, center-to-center was consistent at 6.700″ and rod sideplay was 0.012″ (a previous article listed sideplay as 0.0020″ which was a typo…sorry…slip of the keyboard). It’s a real joy to deal with quality stuff such as this. Lunati deserves a salute for their attention to detail.


An oiled brass thrust washer is slipped over the cam nose.


The cam adapter is then placed onto the cam nose. Jesel recommends sealing the rear face of the adapter to the cam nose with RTV.


The cam adapter is secured to the cam with three torx-head 5/16″ screws, tightened to 30 ft-lbs. The bolt threads are coated with RTV. The supplied spanner wrench holds the adapter in place during tightening. Jesel thoughtfully includes a T-45 bit in the kit.


An oiled brass thrust washer is then placed on the cam adapter flange.


To avoid damaging the outer sealing flange, remove the cam gear’s locating key from the adapter.


A pack of three shims are supplied with the kit. Jesel recommends installing all three initially. After checking cam end play, you can then decide if a shim needs to be removed to adjust this.


With the shims in place, the outer flange is installed and secured.


With a dial indictor in place, I checked cam end play. While my initial check found 0.017″, Gressman suggested that he’d rather see 0.006 – 0.010″, so I may remove one of the 0.010″ shims to fine tune this.


Before installing the cam gear, the key must be reinstalled to the cam adapter.


The crank gear is keyed and slips over the snout easily, to a point about 0.384″ short of full fit.


Note the chamfer on the rear of the crank gear. This will nestle against the snout base chamfer.


Using the supplied aluminum driver and a hammer, the crank gear is interference-fit installed fully onto the crank snout.


With the cam gear and adjuster plate in place, the cam gear locking flange is lightly installed (just enough to engage the key). With the cam gear-to-adjuster plate nuts installed by about one and a half turns, the cam gear is tilted forward at the top to allow belt installation (engage the toothed belt onto the crank gear first, then crawl the belt onto the cam gear).


Final installation should feature the top dot of the crank gear aligned with the bottom dot on the cam gear.


Our Jesel belt drive system fully installed. The belt drive remains exposed, with no outer cover needed.


In order to degree our cam, the folks from CamLogic paid a visit to our shop and set up their system on the motor. Shown here is the CamLogic encoder (mounts to the crank), and digital display unit, a cam lobs dial indicator and a piston indicator.


The encoder slips onto the crank snout via an aluminum keyed adapter. The encoder body is then secured (to prevent body rotation) to the block face.



Note: The cam bores feature sharp edges. To aid in camshaft bearing installation, first deburr the edges with a sharp scraper. Once all block grinding, tapping, and deburring was finished, the block was thoroughly washed, rinsed, and blow-dried, with 5W30 engine oil applied to the cylinder walls to prevent surface-rusting. The camshaft bearings (supplied by Dart) installed with no muss or fuss. By the way, these cam bearings, included with the block, are already coated with an anti-friction material (likely a moly graphite derivative), which is a nice touch by Dart.
With the Crane steel billet roller camshaft coated with 30W engine oil, the cam was carefully inserted, checking for rotational freedom.


The block front features three NPT holes… two 3/8″ NPT and one 1/4″ NPT, all adjacent to the cam tunnel front hole. Since we plan to use the Jesel belt drive timing system, these NPT plugs must sit flush or below the block surface to provide clearance for the belt drive cover. I simply tapped each hole deeper until the installed plugs were a kiss below the surface. With the original rear NPT threaded holes (one 3/8″ NPT and two 1/4″ NPT), plugs will protrude a bit. To gain clearance for a rear motor plate, these holes need to be tapped deeper as well, or you can drill access holes in a motor plate. We opted to leave the threads as-is, and will drill holes in a motor plate at a later date. All NPT steel plugs were installed using Teflon sealing paste.
By the way, before installing the block’s expansion plugs, deburr the edges to aid installation. They’re a tight fit, so be careful to keep them square. I coated the perimeter of ours with a thin coat of Ultracopper RTV before installation. This provides not only additional sealing insurance but serves as a lubricant during installation.


Our piston rings are from Perfect Circle, including top rings (plasma moly ductile 4.600″ x 0.043″, P/N 300-0242), second rings (4.600″ x 0.043″, P/N 302-0435), and the 3/16″ oil ring package, P/N 303-0362.
Using our Summit Manufacturing and Engineering “Adjust-A-Bore” ring squaring tool, I positioned one ring at a time squarely in each bore, removing to file-fit, rechecking, etc., until I had a top and second ring precisely sized for each bore (I file-fit each bore’s rings and organized them accordingly, per bore location).
Diamond Racing’s Eric Simone suggested a gap of 0.022″ for the top rings and 0.024″ for the second rings.
Following his advice, I file-fit our top rings to achieve an end gap of 0.022″, and second rings for a gap of 0.024″. I used Summit Racing’s new bench-mount ring filer that features a natural diamond abrasive wheel and crank handle. An adjustable ring position locator and fixed front stop allow consistent filing for the entire ring set. I also used Summit Engineering’s new ring squaring tool, which proved very handy. It’s expandable and features a drop shoulder that pushes the ring squarely into the bore at a depth of 0.500″. I measured an out-of-the-box clearance end gap of 0.021″ on our oil ring rails, which is fine (the acceptable minimum is 0.015″).
With the rings installed on our Diamond pistons, I verified a top ring groove clearance of 0.0008″ and a second ring groove clearance of 0.001″. The top ring features a radial depth of 0.170″ with a back clearance of 0.0075″. The second ring features a radial depth of 0.210″ with a back clearance of 0.005″. Radial depth of the oil ring package is 0.195″. I measured an out-of-the-box clearance end gap of 0.021″ on our oil ring rails.
When installing the oil ring package, I first installed the oil ring support rail (supplied with the Diamond pistons). Because the piston pin bore height location encroaches into the oil ring groove area, the support rail provides a floor, or footprint for the oil ring.

Here Scott Gressman installs the bobweights to our crank. Our bobweights were set up at 2383.5 grams each.


Scott uses a spacer to locate each bobweight in identical left/right locations on each rod journal. The spacer drops over the journal.


With the spacer in place, the bobweight is tucked against the spacer and then tightened. The spacer is removed once the bobweight is secured in place.


Scott pulls a bit of weight from our front counterweight as dictated by his Sunnen Pro-Bal balancer.


The rear counterweight wanted a bit more weight, so Scott drilled a 1″ hole through the rear flange and through the rear counterweight. Here Scott taps a heavy-metal slug into the counterweight hole. A fill-slug was also added to the hole in the flange.


Horizontal installation of heavy metal eliminates the risk of a slug flinging out during operation.


Here Scott fine-tunes the balance by grinding a few thousandths off of the rear counterweight.


A final check of our crank endplay showed an acceptable 0.007″ fore/aft movement.


Double spiral locks secure each end of the piston pin. Here Gressman slips one into place using his fingers. He’s definitely better at this than yours truly. I simply stood by during lock installation, taking photos and sipping coffee.


Squaring up the piston rings (to check end gap) was quick and easy, thanks to this bore-diameter-adjustable Summit Engineering squaring tool.


I file-fit all of the top and second rings using this diamond-wheel ring filer from Summit Engineering. The diamond wheel is very aggressive, so care is required to avoid over-filing.


The oil ring support rails are required because of the location of the pin bore (the bore intersects the oil ring groove). Install the support rail at the bottom of the oil ring groove, with the male dimple facing down, centered at the pin bore.


The gap of the support rail. Gap really isn’t critical for this rail, as long as it doesn’t butt together. It should sit inside the groove and not contact the cylinder wall.


Our steel billet Crane roller cam was inserted, with journals coated with Royal Purple Max Tuff lube and lobes coated with 30W oil.


The Jesel belt drive system looks intimidating at first, but it really wasn’t a big deal to install.


The Jesel cover is installed to the block with a big block Chevy stock-type timing cover gasket. The cover is secured with a series of 1/4″x20 socket head cap screws, which I tightened to 50 in-lbs.


Lunati rod big end —619.5 g
Lunati rod small end —275.0 g
Lunati rod total weight —894.5 g
Diamond piston —542.0 g
Diamond piston pin —160.0 g
Diamond oil ring support rail —9.5 g
Clevite rod bearings (1 rod) —49.5 g
Perfect Circle ring pack (1 piston) —46.5 g
1 set spiral locks (4 locks) —4.5 g
Oil allowance —8.0 g

Bobweight total —2,383.5 g




Our shafts rotate and the slugs run up ‘n down. Life is good.

by Mike Mavrigian

photos by author

632-012Clevite coated main and rod bearings were used for pre-fitting and final assembly.
Building a stroker bad boy isn’t a walk in the park, as anyone who has been down this road knows all too well. Paying attention to clearances is a major part of the build. After all, unexpected metal contact can ruin anyone’s day.


Upon inspection during crank and rod mock-up, I noticed (due to the long stroke) the potential for connecting rod big-end contact with the camshaft, so I carefully removed material from the upper shoulder of each rod’s big end. Each side of the big end featured two “humps,” requiring us to remove a tiny bit of material to lower the top humps. This was done at the upper shoulder located opposite of the bearing tang locations. Using a pneumatic mini-belt grinder, I removed approximately 0.025″ from the shoulder, bias-tapering our removal down towards the cap parting line. This basically removed the distinct top hump, creating a soft transition from the outboard edge of the rod bolt hole to the lower hump, just above the cap parting line.
In an effort to avoid creating potential stress risers, I oriented the belt grinder parallel to the rod beam (instead of running the belt 90 degrees to the rod). Once the material was removed using 120-grit belts, I followed up with 220- and 320-grit belts to refine the surface smooth out and blend any grinding scratches, and to soften any sharp edges. I then carefully bead-blasted the ground shoulders to further blend and compact the surfaces.
The need to remove these upper big-end humps was not due to any fault on Lunati’s part, but rather it was necessitated by the extreme stroke that we selected for our crank. In reality, the rods may have cleared the cam, but the situation appeared tight enough that we just wanted to play it safe.


After mock-assembly of the crank, rods and pistons, the crank was carefully rotated to check for possible rod big-end-to-block clearance issues. On average, I found only about 0.032″ of clearance at the tightest point between the rod big end and the block pan rail inboard edge. After marking each location on the rail, I emptied the block and ground pocket reliefs to achieve approximately 0.080″-0.100″ clearance (0.060″ would be adequate, but I went a smidge deeper as long as I was at it). Basically, I cut reliefs at the pan rail inboard edges at a width of 1.05″ (rod big end thickness is 0.990″), a depth of about 0.055″ – 0.065″ and a height from the pain rail surface of about 0.300″. I used a die grinder with a spiral-tooth radius-nose cutting bit to create the pockets, followed by a smooth-out and blend with the mini belt grinder, using 120-grit belts followed with 320 grit.
While the rod big-end clearancing allows the rods to clear the cam, I noticed that these same rod big-end shoulders rotate very close (“ouch-close”) to the inboard edges of the cylinder bore bottoms (to the tune of about 0.015″-0.020″ clearance). To gain insurance clearance here, I ground an additional 0.080″ or so, creating wide pockets to clear the rods.
Test-fitting is always a good thing, rather than simply assuming that anything will provide a quick “bolt-on.” Our Jesel belt drive timing system features an aluminum base housing that attaches to the block front face. Upon checking for fit, we noted that the housing would not sit flat on the block. The problem was found to be a slight interference between the left backside shoulder of the aluminum housing to the block, caused by a slight protrusion in the block casting on the left side of the cam tunnel, next to the block’s timing cover mounting flange. A quick grind-down relief of the hump and the edge of the aluminum housing shoulder fixed this. Actually, since the Jesel belt drive housing is a custom piece (completely unlike an OE timing cover), Jesel’s instructions note that some clearancing may be needed. It was no big deal, but it serves as an example that you shouldn’t assume anything (it’s also a good example of why you should always read the instructions).
As a final step, I (just for fun) mildly attacked the block exterior with a die grinder tool and Scotch-brite pads, simply to “dress” the exterior surfaces, eliminating casting line protrusions, etc., prior to block painting. I didn’t get too carried away…just a kiss here and there.
Once all of the grinding was done, I washed the block with hot soapy water, rinsed thoroughly, blow-dried (and lightly oiled the cylinder walls). After the block was completely dry, I applied two medium coats of Plastikote Cast Aluminum engine paint, P/N 282. This provided a pleasing satin aluminum appearance. I followed this with two medium coats of Plastikote 292 engine clear to obtain a slight gloss and added surface protection.


All main cap bolts were tightened to 100 ft.-lbs. (with threads and bolt head undersides lubed with oil).


Rods and pistons installed during test fitting.


Initial clearance between rod big ends and block pan rails was measured at about 0.030″ – 0.032″, due to the stroke of our crank.


Using a bull-nosed cutting bit, I shaved additional clearance to achieve approximately 0.100″ clearance (0.060″ would be an acceptable minimum).


Here’s a finished pocket for rod clearance.


This view (through a lifter valley oil drain slot) reveals tight clearance between the rod big end and the bottom of the cylinder inboard edge. I ground additional clearance at all cylinder bottoms to provide approximately 0.100″ total clearance.


In order to allow the Jesel belt drive cover to sit flat on the block face, minor clearancing was needed at this hump (marked here in black). I only needed to remove about 0.030″ of material from this spot.


Our rod big end shoulders (located opposite the bearing tang side) needed a thickness reduction to avoid contacting the cam. This small hump on the top of the shoulder needed to be ramped down.


Using a mini belt grinder, the shoulder was reduced, biasing the angle towards the cap.


Here’s a shoulder after grinding.


Following grinding, I carefully bead-blasted the ground area to soften edges and to compact the surface.


Here we begin weighing our Lunati rods. All small ends were identical. Even after our clearancing of the rod big-end shoulders, big-end weights were so closely matched that no further weight corrections were needed.


All of our Diamond pistons matched, so no lightening was required.



The valve reliefs were cut with precision. The intake pockets are 0.270″ and exhaust pockets are 0.064″.


Notice that the pin bore location encroaches into the oil ring groove. Diamond supplied a set of support rails that are installed prior to the oil ring package. These provide footprint support for the oil ring package.


Scott Gressman torques the honing plates to our block, tightening to 70 ft-lbs.


Before honing, Gressman grinds clearance on the center main webs to prevent stone damage.


A view through this bore shows the slight material removal necessary for honing stone clearance (see the area below the cylinder wall).


This closeup provides a better view of the small casting “hump” on the main web, after Gressman removed about 0.030″ of material.


Each cylinder was honed to 4.599″during the first honing stage. Final honing opened the bores up to 4.60075″.


Piston diameter is made 90-degrees to the pin bore, at 0.700″ below the ring land.


Gressman verifies honed size prior to plateau finishing.


In order to finish the bores, Gressman used silicon carbide brushes. This will provide good seating for our plasma moly top rings.


Our finished cylinder walls.


This closeup shows the brush-finished hatch pattern.


While at Gressman’s shop, we mocked up one rod to check for rod-to-block clearance.


Dart thoughtfully clearanced the block for stroker crank use. In our case, our Lunati counterweights cleared the block by a mile (actually, the tightest area was about ?”), so we’re fine with regard to crank fit.


Our Lunati 4.7500″ stroker crank was extremely well finished, with mains all the same diameter and rods all the same. Every journal was ground straight, with absolutely no taper to be found. Nice job, right out of the box.


While test fitting our crank, we used the bearings that we’ll install during final assembly. All of our Clevite bearings have been treated to a special anti-friction coating, which Clevite tells us is even better than conventional moly graphite.


This view through the cam tunnel shows a potential clearance issue between the rod big end and the camshaft. Just to be safe, we’ll remove a bit of material from the rods. This is not uncommon when dealing with a long stroke.


Here Gressman points to the area of the rod that should be clearanced (at his fingertip).


This view clearly shows the area (the small radius hump) adjacent to the bolt hole exit that we’ll relieve. We’ll probably only remove about 0.020″ or so, at a slight angle that leans towards the rod beam.


In each case, only one hump needs to be relieved on each rod. This is the hump that is opposite the rod big end’s bearing tang area.


After we grind a small bit of material from each rod big end, we’ll rebalance our rods.


Each of our main journals measured exactly the same, at 2.7495″.


Our installed main bearings measured 2.7535″.


All rod journals measured 2.200″.


Each rod bearing (installed, with caps fully tightened to 70 ft-lbs w/moly), measured 2.2035″. We’ll monitor bolt stretch during final assembly.


Our special thanks to Gressman Powersports
for honing our block’s cylinders to size.

Gressman Powersports
For more information, dial 1-800-652-0406, ext. 13415
Online, visit

Thanks to the following for their involvement in this project …

For more information, dial 1-800-652-0406, ext. 13416
Online, visit

For more information, dial 1-800-652-0406, ext. 13417
Online, visit

For more information, dial 1-800-652-0406, ext. 13418
Online, visit

For more information, dial 1-800-652-0406, ext. 13419
Online, visit

For more information, dial 1-800-652-0406, ext. 13420
Online, visit

For more information, dial 1-800-652-0406, ext. 13421
Online, visit

For more information, dial 1-800-652-0406, ext. 13422
Online, visit

For more information, dial 1-800-652-0406, ext. 13423
Online, visit

For more information, dial 1-800-652-0406, ext. 13424
Online, visit
For more information, dial 1-800-652-0406, ext. 13425
Online, visit

(see Holley Performance Products)

For more information, dial 1-800-652-0406, ext. 13426
Online, visit

For more information, dial 1-800-652-0406, ext. 13427
Online, visit

For more information, dial 1-800-652-0406, ext. 13428
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For more information, dial 1-800-652-0406, ext. 13429
Online, visit지



Following a recommendation from our buddies at Sunnen, we visited Gressman at Gressman Powersports in Fremont, Ohio (Gressman has built a number of 632 motors, in addition to countless big-number drag, sprint car and road-race engines). Naturally, the Ohio winter weather forced us to drive in sub-zero temperatures. Even with the block boxed and wrapped in the bed of my dually truck, it looked like a gray Popsicle when we arrived at Gressman’s (it may have been cryo treated as a result of the two-hour drive … just kidding … sort of), so we allowed the block to warm up for a while before we began messing with it.
With the block at room temperature, we measured the Dart block’s bores, noting a raw diameter of 4.590″ (Dart leaves enough material to allow the builder to obtain desired diameter). Since our Diamond pistons measured 4.59375″, we needed to remove a total of 0.01075″ in order to achieve the desired 0.007″ clearance.
After confirming that our main caps were snugged to 100 ft-lbs, Gressman mounted a pair of BHJ deck plates (tightening these to 70 ft-lbs).
Before honing, Gressman used a hand grinder to knock a bit of material from the webbing surfaces below the center three cylinder areas where the bores Siamese (small humps are featured in the casting) to prevent damage to his honing stones. This took only about 10 seconds per spot, so it was no big deal.
He then began honing with 500-grit diamond stones with a high load setting to hog out the bores to an initial 4.599″, followed by a final honing pass to remove the remaining 0.00175″. All cylinders were then treated to four passes with silicon carbide brushes at 30 percent load for a plateau finish. Because of the amount of material removed from the start, the entire honing process took about an hour and a half. Gressman noted that the high-quality Dart blocks feature a high nickel content (he mentioned that these blocks are about 30 percent harder than “common” iron blocks), which requires increased honing time as compared to most OE blocks.
By the way, Gressman recently purchased an RMC/Sunnen V40 multi-axis CNC machine, which the shop uses for a variety of operations, including block clearancing, cylinder boring, lifter bore correction, and block lightening (for race applications). I wish that we had the luxury of time to take advantage of a block lightening job (if for no other reason than to make the block look even cooler), but we were on a tight deadline, so I left without having a chance to see the CNC in action.
By the way, Gressman’s shop was a thing of beauty. We definitely plan to revisit in the future. This is a very nice operation and clean as a whistle.

Our pistons began life as high-density slugs.


Domes were cut flat and pin bores were roughed in at the beginning of the transformation.


A view of the unfinished pin boss area.


The outer body was machined to desired diameter and the rind grooves were cut. Notice the big chamfer cut on the top. As you can see, quite a bit of material will be removed during the machining process.


The skirts were shortened and the domes were cut to height, along with the valve pockets. Notice the huge hunk of aluminum that was removed at the pin bore sides, to remove unneeded weight.


Gas porting holes were drilled along the perimeter of the top.


The underside was finish-machined for additional weight savings.


Skirt diameter was verified for each piston before shipment.


That’s a bunch of pistons. Diamond has earned a solid reputation for quality.


Closeup view of a piston underside.


A view of a finished piston as we received it. While weight was shaved everywhere possible, no compromises in strength were made.


This view shows the deep weight-saving relief at the pin bore side.


The pin bores were polished with a mirror-like finish and pins were carefully fitted at Diamond’s facility. Note the deep location for the spiralock grooves.


Gas ports will aid in top ring stability and sealing.




We hone the block and determine bottom-end clearances.

by Mike Mavrigian

photos by author

632001a1With our new pistons in hand, it was now time to hone the cylinders to size.
As you may recall from our previous article, our target is to build an all-motor 632 cubic-inch big block featuring 15:1 compression, enabling us to produce approximately 1,200 HP in the mid-7,000 RPM range.
Now that our pistons have arrived, we were able to hone the cylinders to final size. We’ve also measured critical clearances for bearings, crank-to-block, rod-to-block and rod-to-cam.
In the third installment of this multi-part series, we’ll paint the block, balance the rotating assembly and begin our test assembly for final fitting.


As mentioned in Part 1, we enlisted Diamond to make our custom pistons. Well, the little buggers arrived, and they’re gorgeous. Did I say little? At a measured 4.5937″, they’re ‘ huge. If these billet beauties were adult human females, I’d ask them out on dates. Yeah, they’re that pretty. If we had room in the magazine, I’d shoot two-page spread photo of these parts.
Okay, maybe that was a bit over the top, but you can’t blame a guy for getting excited. When I think about how these puppies are going to squeeze against the Dart Big Chief 2 chambers, I can’t help getting all giddy with anticipation.
The pistons began as high-density forgings (DRP76X), and were CNC machined to the finished state. The custom dome features a dish, along with valve reliefs for both intake and exhaust valves. The intake valve depth is 0.270″, while the exhaust valve depth is 0.064″. Total dome volume is -21.1cc. Combined with a compression height of 1.120″, 0.005″ deck clearance, our Victor MLS gaskets and the 56cc combustion chambers, this should give us a tidy 15:1 compression ratio.
Features of these pistons include the use of their P/N 9310 piston pins (0.990″D x 2.930″L x 0.165″ wall), gas porting along the dome perimeter (these ports will aid in ring seating and eliminate flutter), and a serious weight-savings via their internal mill “Maxi-Lite” machining.
Because of the extremely compact ring groove layout, the pin bore encroaches through the oil ring groove. In order to provide a “floor” for the oil ring package, Diamond included a pack of its oil ring support rails that features a 0.188″ wall. These will provide bottom support for the oil ring in the pin bore passage areas. The pins are full-floaters, and are designed to be secured via Spirolox retaining rings (0.990″ x 0.043″).
Diamond noted that the installed wall clearance for these pistons should be 0.0070″. It specifies that piston diameter must be measured 90 degrees to the pin bore, at a distance of 0.700″ down from the oil land.


We first verify-measured our main bearing bores, which mic’d out at 2.9375″.
We mock-installed the steel Lunati 4.750″ stroker crank (P/N BS-421 MN) using our Clevite Tri-Armor main bearings #MS-829 HXK, tightening the main cap bolts to a value of 100 ft-lbs (with moly on threads and bolt underheads). Installed main bearing diameters measured at 2.7535″. Our crank main journals mic’d at 2.7495″, providing us with main bearing clearance at 0.004″. According to Scott Gressman at Gressman Powersports, this build requires bearing clearances on the “loose” side. Crank endplay measured 0.008″.
One obvious concern, given the 4.750″ stroke of this crank, was counterweight-to-block clearance. Happily, we had gobs of clearance, with the tightest spots at about a healthy 1/4″. This required us to do nothing but grin in terms of counterweight clearance. The boys at Dart obviously gave some thought to boneheads like us using a long stroke and machined the block accordingly.


(rod bolt stretch should be —0.005-0.0055″)


Using our Clevite Tri-Armor rod bearings, part #CB-743 HXK, we test-assembled all of our Lunati Pro Mod steel rods (with pistons in place), tightening the ARP 200 7/16″ rod bolts to a stretch value of 0.005″ to 0.0055″ (70 ft-lbs with moly if torqued). With our installed rod bearing diameter at 2.20325″ and our rod journals at 2.200″, we obtained oil clearance at 0.00325″. Rod sideplay was measured at 0.0020″ at all rod journal locations.
While checking for rod big-end to block clearance, we noted adequate clearance with the tightest at about 0.050″, but we’ll likely kiss the block in a few spots just for safety’s sake.
When we mocked-up a piston/rod assembly onto the crank and rotated, we noticed a portion of the rod big end encroaching into the cam tunnel. The radius hump on the upper portion of the big end needs to be reduced slightly (maybe 0.020″ or so) to ensure camshaft clearance. Considering the 4.750″ stroke, this didn’t come as a big surprise. We’ll relieve this small hump (the hump opposite from the bearing tang side) and re-balance the rods. You’ll see this in the next issue.


Finished bore size —4.600″
Stroke — 4.750″
Rod length —6.700″
Block deck height —10.200″
Piston to deck —0.005″
Compression height —1.120″
Cyl. bore length —6.350″
Piston type —conical dish
Piston material — 2618
Valve depth —INT 0.270″
—EXH 0.064″
Effective dome volume —  -21.1 cc
Piston weight —542 grams
Required bore clearance —0.007″
(measured 90 degrees to the pin hole, at 0.700″ below oil land)

Engine type —BBC
Application —Drag race
Desired comp. ratio —15.00:1
Cylinder head —Dart Big Chief 2
Chamber volume —56.0 cc
Comp. gasket —0.045″
Gasket bore dia. —4.640″
Gasket volume —12.47 cc
Top land —0.285″

Int. depth —0.270″
Int. valve dia —2.470″
Exh. depth —0.064″
Exh. valve dia — 1.800″
Int. angle —11 deg.

Lunati steel I-beam Pro Mod P/N LB01
Rod length —6.700″
Small end width — 1.133″
Thickness above pin —0.210″
Material steel

SKIRT SHAPE window type full roundDart CNC machined the block so all critical bore locations and sizes were already correct and to-size. Only the bores remained to be honed for proper piston clearance.


Dart CNC machined the block so all critical bore locations and sizes were already correct and to-size. Only the bores remained to be honed for proper piston clearance.


The initial bore diameters, as delivered from Dart, measured 4.590″.


Our billet pistons from Diamond were custom-made specifically for our combination of the 10.2″ deck block, 6.700″ rods, Big Chief 2 11-degree heads and 4.750″ stroker crank.


Diamond’s pistons are things of beauty, in addition to having the inherent quality that Diamond is known for. Our dome volume is -21.1cc. In combination with our block height, rod length and combustion chamber size, we should realize 15:1 compression ratio.


Our custom piston spec sheet. We carefully went through each item with Diamond’s Eric Simone, who was extremely helpful and knowledgeable.

Crane Cams Tech Support (Part 2)

• “Bling Bling:” So a customer has a new Denali or Escalade with some “Dubs,” (rims for the old folks), and wants the speedometer to display the correct speed. The customer also notices he or she doesn’t have the power the truck had before he or she put those 26″ dubs on!
So how about getting that speedometer corrected and getting that power back? Crane’s new Power Tuner can add up to 30 HP and 35 ft. lbs. of TQ at the rear wheels (for the gasoline engines). The Power Tuner will take care of any tire size change from 25″-44″, gear ratio change from 2.73-5.13, cam changes, adding a Supercharger, how firm a shift you would like, adjust tuning for the fuel you use, changing or eliminating the speed limiter, and even clearing trouble codes. Look on Crane’s Web site and find applications for the new Power Tuner by visiting the following link:

• Valve Stem Diameter: A number of the aftermarket big-block Chevrolet 396-454 V-8 cylinder heads currently being sold are equipped with 11/32″ diameter valve stems instead of the stock 3/8″ stems. When ordering valve spring retainers and valve stem locks (“split keys”) for these applications, be sure to check the valve stem diameter in order to achieve proper fit the first time.

• The Harley-Davidson Twin Cam 88: The Harley-Davidson Twin Cam 88 engine has no provision for changing cam timing. Crane Cams has solved that problem with a reversible crank sprocket, Part # 7-3000. This crank sprocket will allow you to advance the engine’s cam timing by four degrees for more bottom-end torque and acceleration, reverse it to the four-degree retard position for more top-end power, or decrease cylinder pressure if a detonation problem occurs.

• Truing Lifter Bores: One of the more popular steps in preparing a big-block Chevrolet 396-454 V-8 engine for racing (or street performance) involves truing the lifter bores to ensure their proper bank angles and squareness.
Once the block has been machined, the lifter bores are often bushed back to their standard (0.842″) diameter. As it isn’t common to remove more than a few thousandths during the truing process to bring the lifter bores into spec, it is possible to save time (and money) by boring the block to use either Crane’s 0.875″ or 0.904″ diameter roller lifters and not have to bush the bores.
These Ultra-Pro series rollers are offered in both centered and offset intake pushrod seat versions and provide the latest technology available in Crane’s roller lifter program. The 0.904″ versions also feature their 0.815″ diameter wheel/axle/bearing assembly which provides significant increases in strength and durability as compared with the usual size 0.750″ assemblies.

• Special Grind Cams: Special grind cams are a great options Crane offers. The company can change durations/lift/lobe separations and centerlines, etc. This is perfect for the racer who always must have the edge on the track. Because this special grind is made for a specific customer, that combination may not work for someone else. That’s why these special grind cams are a non-returnable item. For that reason, Crane wants to make sure that what you are asking for is exactly what you want.

• Matching Coil and Ignition: If you’re building a custom Harley-Davidson make sure you match your coil with the ignition you’re using. If you’re trying to build a nostalgia bike and are using a kicker or points, that would require a 5-ohm coil. Later year Shovelhead or Evolution engines with electronic ignitions take a 3-ohm coil, and if you’re going all out with the new Twin Cam 88 engine for a custom bike, that would require a special coil which has only 5-ohm resistance.

• Let The Air Out: The Gen 4 big-block Chevy must have the front lifter oil galley plugs modified by removing them and drilling a 0.030″  hole in the center of the plug before reinstalling them. This hole will bleed off any air lock in the front of the lifter galley oil passages. This air lock can cause the front lifters on each side to get air in the lifter, starve the oil to the rocker arm and, of course, make noise because the lifter will not pump up.
GM started drilling the plugs in the late 1970s, early ’80s and produces a change bulletin to modify any older engines that were being rebuilt or that had dry lifters in the front of the engine. Also, the oil that then comes out of these holes will also lube the timing chain and gears as a bonus.

• Valve Lash: On Ford 1971-74 2000cc I4 camshafts and Ford 1974-87 2300cc I4 engines equipped with mechanical followers, the valve lash is measured between the camshaft and the follower, not the follower and the valve stem. Measuring incorrectly can result in incorrect valve timing and a probable reduction in performance and reliability.

• Chevy 60 Degree V-6 Camshafts: The Chevrolet 60 degree V-6 camshafts listed in Crane’s current catalog are for distributor equipped engines only. In 1991 and later applications, some vehicles used a version of this engine that was distributorless. In these instances, these camshafts will not install and function properly. However, Crane can regrind distributorless type camshafts to their specifications. Please contact Crane’s Tech Department at (386) 258-6174 for more information.

• GM’s Gear Marking Compound: General Motors sells a compound to aid the inspection of the gear mating. It is GM “Gear Marking Compound,” Part #1052351, and is available at GM dealerships. This compound can be used in many applications, such as inspecting a ring and pinion gear or mating the cam distributor drive gear. To use it to check a distributor, the compound must be brushed all the way around the distributor drive gear. Then, install the distributor into the engine using whatever gasket and hold-down device you plan on running. Tighten the distributor in place. Use your hand to hold the distributor rotor to provide some resistance to the rotation of the distributor (this is to simulate the load on the distributor drive gears). Now, hand turn the engine over at least two full turns of the crankshaft. (Remember, it takes two crankshaft revolutions to generate one camshaft revolution.) Then carefully remove the distributor and inspect the wear pattern marked on the compound.
You may find that the distributor location might need to be spaced up or down to move the wear pattern as close to the center of the distributor gear as possible. (Some distributors have adjustable hold-down collars to assist in this adjustment.) Next, you want to see how the teeth are mating to determine whether the gear lash is too tight or too loose. In certain cases, there are oversized distributor gears available that can be used to assist in the gear lash adjustment.

• Installing Reground Cams and Lash Caps on 4.6L-5.4L Fords: You must measure the amount of clearance between the roller rocker arm and the base circle of the cam. This will ensure that you have the correct clearance for your reground cams.
When the cams are reground, the size of the base circle is reduced, which means you will have to run lash caps to make up the difference. Since you have changed the size of the cam, you will want to make sure you have the same clearances as before. To do this, compress the lifter until it is solid and then install the rocker arm and cam. You are looking to get between 0.018″-0.032″ of clearance between the roller rocker arm and the base circle of the cam. This will ensure that the rocker will stay in place while the engine is being assembled.
If you have a clearance larger than 0.032″, you will need to put a shim under the lifter to get your clearances correct.

• Oil Restrictors: Crane doesn’t recommend running oil restrictors because they will starve the top end of a motor. This lack of oil will not prevent the components from being lubricated or cooled by the flow of oil, which is necessary to remove the heat created from pressure and friction. This, in turn, will create excessive wear and shorten the life of the springs, valves, guides, rockers, lifters, etc. On Crane’s Shaft Mount rockers, oil is necessary to the longevity and life of the bearings. So, if you do run oil restrictors, you must open up the restrictors to 0.100″ to ensure that you’re applying enough oil to the rockers.

• Mopar Ultra Pro Roller Lifters: With all of the new Ultra Pro roller lifters that Crane has recently released for Chevrolet and Ford applications, some of the Chrysler-oriented folks are wondering about availability for their engines.
The good news is that Crane actually did all of the development work on the Ultra Pro series in Chrysler applications, especially in the harsh environments of supercharged alcohol and Top Fuel drag racing. Crane first released 8620-bodied lifters for these usages more than 15 years ago and have now upgraded them all to the new Monel pin retained locking bar retention system.
To maintain the identity of these familiar items, we elected not to change their part numbers, but to stay with the current 66542, 66543, 66550, 66554, 66547, 66548, 140550, etc. numbered offerings. The 2005 Crane Master Catalog details all of the numbers by application, and explains the differences between the Standard, Pro Series and Ultra-Pro roller lifters.

• 1963 Ford SHC 427 V-8 Camshafts: As the nostalgia market expands daily, there are many folks looking for camshafts for the 1963 Ford SHC 427 V-8 engines. Original cams (either cast or billet) are tough to come by, but there is another option. Roto Faze Products in Torrance, California (310/325-8844) has produced new round lobe 8620 steel billet camshaft cores for these powerplants and offers them to those fortunate enough to have a Cammer.
Once you obtain the cores, you can forward them to Crane for rough grinding, heat treating and finish grinding to any of our dedicated profiles. As Crane was instrumental in the original aftermarket development of this engine in the racing arena, the company can reproduce any of its original grinds and also offers many new profiles for applications ranging from mild street to all-out drag racing.

• 502 Gen 6 Big-Block Chevy Marine Engine Cam Firing Order: If you’re thinking about replacing the camshaft in a 502 Gen 6 big-block Chevy marine engine and would like to try a different firing order, call Crane Cams and get the part number for your new cam designed for the 8.1L engine. The 8.1L camshaft will fit right into a Gen 6 502, but you will have the new firing order of 1, 8, 7, 2, 6, 5, 4, 3. The cams are interchangeable as long as you install your plug wires to match the firing order you have.

• Changing From Iron to Aluminum Cylinder Heads: When changing to aluminum cylinder heads from your trusty old cast iron pieces, you not only lighten up the engine, but you can also affect the ignition timing requirements.
Even though you might have the same exact static compression ratio as with your old iron heads, the aluminum heads dissipate heat much more effectively, resulting in a similar effect to lowering the compression ratio from 0.5 to 1 full point depending on your overall combination. Therefore, with aluminum heads, you can usually run a higher compression ratio and/or more ignition timing, as the tendency towards detonation will decrease. An aluminum block will also contribute to this effect, though not as significantly. We’ve discussed the valve lash/lifter preload situation with aluminum heads in recent Tech Tips, so refer back to those when setting your valves.

• Oil Drip: To ensure better oiling on your small-block Ford, drill a .030″ (1/32″) hole in the plug above the distributor gear under the timing cover. This will make a fast drip on the distributor gear, which will extend the life of both the gears. This can also help prevent a cutting edge from occurring on the cam gear if you’re running a high-volume oil pump.
• Flat Tappet Going Flat: First of all, the hydraulic or mechanical flat tappet lifters need to rotate in the lifter bore to get an even wear pattern. This will keep the cam and lifters running smoothly. So, setup will be important on a flat tappet cam. Spring pressure can be too high and not allow the lifter(s) to rotate in the bore during break-in. So if you are running dual springs, you will need to remove the inner springs to reduce the pressure on the lifters during break-in. Also, do not run a synthetic type of oil for break-in.
Before the installation of the cam and lifters, do not soak or pump up the hydraulic lifters! This will only make the lifter lock up and cause more problems when setting a pre-load into the lifters. Of course, you will need to apply the assembly lube (Part #99002-1 is 1 oz.) to the cam lobes and lifters. Using break-in lube (#99003-1 is 8 oz.) in the oil is another great precaution to take since oil formulations have changed during the past few years.
On the hydraulic lifters, you will need to set a preload into the lifter between 0.020″-0.060″. If you do not set any preload into the lifter and run it at zero lash, you have now tried to make the hydraulic into a mechanical lifter, which will pump up the hydraulic lifter, again causing a load on the lifter face.
After you have set your pre-load (hydraulic) or lash setting (mechanical), you will need to make sure you prime the engine and get oil up through every rocker arm, even if this takes a half-hour (big-block Chevy). Another precaution to help you during break-in is to take some white-out or paint and put a small stripe on the top of every pushrod. Before you start up the vehicle, use a clear or cut-away valve cover to watch the pushrods. After start up, watch all of those pushrods and make sure they are all spinning. If the pushrods are spinning, the lifters are also spinning, and there should be no problem through the break-in period. Remember to keep your RPMs between 1,500-3,000 and vary the RPM. Do not leave the engine at a set RPM! Varying the RPM will change the oil splash to the lifters. Also make sure your break-in period is no shorter than 20 minutes (and up to 30 minutes).

Crane Cams Tech Support (Part 1)

Crane Cams Tech Support

By Crane Cams Tech & Customer Service Dept.

We managed to glean a host of informative technical tips from the boys at Crane Cams.These tips cover a range of subjects from distributor gear wear to V-Twin motorcycle cams, and we think you’ll find them helpful.
• Distributor Gear Wear: It has come to the attention of Crane’s Tech and Customer Service departments that premature cam distributor gear wear and breakage can occur. The two practices that can cause gear wear are running a high-volume or high-pressure oil pump or reusing an already worn or damaged distributor gear with a new cam (or vice versa). In this case the distributor gear or cam gear has worn into a pattern and may not mesh with the new part. This can cause breakage and/or continue to prematurely wear out the gear.

• “Good” vs. “Rough” Idle: What does “good idle” and “rough idle” actually mean? Compared with what? Smooth and good idle represents a stock or near-stock idle, 600-800 RPM with a high vacuum signal. Rougher idles are higher idle speed, 850-1200 RPM, lower vacuum signal. The engine actually seems to shake (rough) with a rough idle camshaft.

• Pushrod Length and Rocker Geometry: What’s the best way to check whether this is too long or too short? Here are some do’s and don’ts. Do use Crane’s adjustable checking pushrods. Don’t use other dummy rocker arm fixtures (on the head stud checker). Do set the lash by hand at zero. Do blue the end of the valve stem. Do run the engine through two intake and exhaust cycles while observing the tracking of the roller wheel. Do adjust the checking pushrod in or out until you achieve the exact equal tracking across the top of the valve stem. If you are checking a hydraulic engine, use a solid lifter during this procedure.

• V-Twin Motorcycle Cams: Single overhead cam, roller follower, air cooled, 1000cc V-Twin? Sounds like one of the latest state-of-the-art Metric cruiser offerings? No, Crane is currently producing an exclusive batch of camshafts for the 1914 Cyclone Track Racer motorcycle engines. For a short time, these engines dominated board racing in the shorter duration events, with Indian and Harley-Davidson as their closest competition. The leading restorer of these unique bikes (of which only a handful exist in the world), Stephen Wright, depends on Crane Cams to ensure that only the highest quality camshafts are used in his masterpieces.

• Power-Tuner: For vehicles with daytime running lights, you will need to set the parking brake before turning the key to the “ON” position. This will turn the DRL off. If this is not done, it may interfere with the programming.
• “Kickback:” When, and if, it happens to a Harley, it can be very expensive to deal with and usually can be prevented easily. A Harley bike has an inductive-type ignition system that will fire when the current in the primary of the coil is switched off. If your battery is low during cranking, the current in the coil can go low enough to enable it to fire the spark plug. If this occurs with the piston in the wrong position, kickback can occur. This usually results in broken gears and a “hurt wallet.” Make sure your battery is maintained and that your starter can turn your motor over without starving the ignition system. To help eliminate a kickback condition, the Crane Cams ignition modules allow the motor to turn over for two revs before the ignition turns on. Another engineering perk to help you.

• Regrinding Used Camshafts: In those cases where Crane doesn’t offer an outright cam core for your particular application, the company can probably regrind your good used camshaft. Cams that do not have severely worn lobes can usually be reground. However, many folks don’t check for worn distributor drive gears or fuel pump lobes before forwarding them to Crane. Also, the cam’s journals should be in good shape. Crane can’t repair worn journals, distributor gears or fuel pump lobes, so be sure to check your camshaft thoroughly before considering it for regrinding purposes. Severely bent cams (over .030″) also aren’t good candidates for regrinding.
• Mechanical Lifters Camshafts: When using mechanical lifter camshafts in Ford FE 352-428 V-8 engines, Crane recommends its 99256-16 shell-type mechanical lifters (along with their 34642-16 pushrods); however these lifters are now no longer available. The 99257-16 standard-style mechanical lifters are now advised, along with Crane’s 34645-16 pushrods. These can be used with either Crane’s 34772-16 ductile iron adjustable rocker arms or the company’s new 34790-16 adjustable aluminum rocker arm kit.

• Springs for Aftermarket Heads: If you’re purchasing aftermarket heads complete, decide which cam you’re planning to use so you use the correct spring pressures. Most consumers look at the maximum lift that the springs can handle and don’t pay as much attention to the seat and open pressures. If you’re planning to use a flat tappet cam, Crane suggests you purchase the heads bare, then outfit the heads with the required springs so prevent wiping out the cam due to too much spring pressure for the flat tappet cams.

• V.O.E.S. (Vacuum Operated Electric Switch) for Harley Davidson: The V.O.E.S. is a vacuum advance, not a retard unit. It’s designed to advance the ignition timing when the engine isn’t under load. All dressers should advance at 5.5″ to 6.0″ of manifold vacuum; Softails and Dyna Glides around 3.5″ to 4.5″. Sportsters should advance at 3.0″. On all motors that have increased compression ratio or a performance cam is installed, set V.O.E.S. at 5.5″.

• American Motors/Jeep and Chrysler/Dodge/Plymouth Mechanical Lifters: The 99260-12 and 99260-16 mechanical lifters for the American Motors/Jeep 199-258 I6 and 290-401 V-8 engines, along with the Chrysler-Dodge-Plymouth 273-360 V-8′s are now available. These had been in short supply for a couple of years, but are now in stock. These are .904″ diameter, capable of carrying oil up the pushrods, and can also be used in non-pushrod oiling applications. Current suggested resale prices are $125.76 for the 99260-16 and $94.32 for the 99260-12. Standard discounts apply.

• What Goes In Must Get Out!: One of the biggest performance mistakes many street performance enthusiasts make is to not provide enough exhaust capacity for the horsepower level they are trying to achieve. Installing a bigger cam, aftermarket cylinder heads and a high-flow intake system is of little use if you can’t get the air out of the engine as well.
For maximum power and driving pleasure, tubular exhaust headers are recommended for any camshafts with durations at .050, lifter rise of 210 degrees or greater. Failure to provide adequate exhaust with large camshafts results in poor idle quality, hesitation on acceleration, part throttle surging, poor power brake performance, etc. Due to design considerations, some body styles (such as the 1982-1991 GM F-bodies) have extremely limited space for enlarging the exhaust. You should consider this limitation when selecting a camshaft for a vehicle. Less power is lost by slightly undercamming rather than overcamming.

• Hydraulic Roller Tappets: If you’re going to install a performance camshaft with higher valve lift in your 8.1L Chevy big-block engine, make sure that you check your hydraulic roller tappets. If you go too low in the lifter bore, they could bind or fall out of the original hold-down plate, causing severe damage to the engine and valve train. To solve this problem, Crane Cams has developed a taller lifter, which is made for higher valve lift and will work with the factory hold-down assembly. Use Crane Cams hydraulic roller tappet Part #26535-16 for that application.

• New Spring Application: For anyone putting Chevy Vortex heads on early 350 V-8s, Crane has a new spring and retainer for these heads. This is a dual spring that will fit the stock spring pockets with no machining. (Note: the valve guides must be trimmed to .531″ diameter and the appropriate valve guide seal used).

Part Numbers:
Springs #144832-16
Retainers #99975-16
(new multi-fit)
5/16″ Locks #99093-1
11/32″ Locks #99094-1

The valve stem locks are our multi-fit style and are available in +/- .50 heights. You will need a spring shim on the bottom of the spring when installing. This can be used with hydraulic flat tappet or roller cams. Also, remember to use our Gold Rockers (#11750-16 1.5 ratio, #11759-16 1.6 ratio) to complete the change.

• Generation IV, V, and VI Big Block Chevy: The Gen IV engines all come from the factory with flat tappet cams (1967-1995). Gen V engines still use a flat tappet cam and started using a 360′ crank seal, single row timing chain and gear set and non-adjustable rockers (‘95). Some Gen V engines were made with hydraulic rollers for marine applications only.
There is no core for these hydraulic roller cams, so a Gen IV Retrofit hydraulic roller cam must be used as a replacement, along with a double roller, timing chain and gear set with an Imco (909-592-6162) timing cover to match. The Gen VI engine comes as a hydraulic roller (1996-2000). This engine also uses a single-row timing chain and gear set, 360′ crank seal and non-adjustable rocker arms.



Roller bearings for camshaft tunnels offer increased timing precision, reduced operating friction and the ability to handle higher loads.

by Mike Mavrigian


An alternative to traditional cam bearings is the needle roller bearing, which provides increased stability and durability for extended high-RPM racing applications.

Because of the expense of block machining and the resulting dedication of that block to the use of roller bearings, the move to roller type camshaft bearings isn’t for every build. If the mill is used in short-run drag applications, the modification likely won’t justify itself. If the engine is intended for street use only, switching to roller bearings is just plain stupid and a total waste of money. If however, the engine is being built as a dedicated screamer at its upper end for long periods of time, the move to roller cam bearings makes all the sense in the world. Due to the nature of fitting roller-type camshaft bearings, the block (and camshaft) must be dedicated to the use of these bearings.


There are a few aftermarket blocks that are already machined for a particular size roller bearing. If you do not have this type of block, then the cam tunnel must be bored to accommodate the specific size of roller bearing that you plan to use. Several O.D. roller bearings are available, including 1.875″, 1.968″ (50mm), 2.125″, 2.165″ (55mm) and 2.362″ (60mm).
If the block needs to be bored to accept roller bearings, it should be obvious that this requires an extremely precise machining operation, both for finished bore diameter and for bore-to-bore alignment. In general terms, the maximum acceptable runout between individual camshaft bore locations is about 0.0005″.
Bear in mind that in addition to machining the cam bores to accept the roller bearings, the cam tunnel run may require clearancing to allow pass-through of the bearings during installation. This may require tedious grinder work or machine-cutting with a carbide bit.
If circumferential cam bore oil grooves are lost during the over-boring (typically at the number one cam bore location), these grooves must be restored.
Note: since the use of roller cam bearings require all cam bores to be machined to the same diameter, this provides the added installation advantage of being able to install rear cam bearings from the rear of the block.



If you plan to take advantage of roller cam bearings, you’ll need to order a camshaft that features journals specific to the size of roller bearings that you plan to use.
When installing a roller bearing in an iron block, the bearing cage should have between 0.0005″ to 0.001″ press fit to the cam bore. If you’re installing the roller bearing in an aluminum block, the bearing cage should have between 0.001″ to 0.0015″ press fit to the cam bore.
For proper installation, Comp Cams recommends using a thermal technique as opposed to pressing the bearings into place under ambient temperature. Comp recommends freezing the bearing and heating the block for safe installation to avoid bearing cage damage.


When installing roller type cam bearings, there is usually no need to block or restrict oil feed holes to the cam bearings. Roller type cam bearings usually require only splash lubrication. However, oil feed holes can be blocked off to reduce oil aeration and windage losses, depending on the application. Also, depending on the application (especially when dealing with a production block), oil transfer grooves (such as found in the number one cam bore in a smallblock Chevy) must be restored following the boring operation in order to maintain proper oil flow to the mains.
Since the use of roller-type camshaft bearings reduce camshaft rotating friction, oil-operating temperature should reduce as well. A slight reduction in oil temperature helps to insure greater oil longevity. This issue of friction as it relates to temperature becomes more pronounced in applications that feature aggressive cam profiles and high valve spring rates. Reducing oil-related heat transfer is always a good thing. Since the oil holes in the cam bores are blocked by the roller bearing cages (and by tapping and plugging the holes if desired), more oil is subsequently routed to the crank main bearings and rod bearings, where it’s needed the most.



It’s simply amazing that any components are able to withstand this nightmarish environment.

by Mike Mavrigian


A Dykes top ring from a Top Fuel engine.

(photo by author)


Note the missing plasma moly that was blown off of this top ring. This ring (and its companion set) saw a mere 24 seconds of running time, from startup to the end of the dragstrip. This particular engine powered the car to a 4.509-second run at 330 MPH.
It’s certainly no secret that Top Fuel drag engines produce horrific levels of power, to the tune of 7,000 to 8,000 HP and torque in the range of 6,000 lb-ft, currently shooting these cars to speeds in excess of 300 MPH. We thought that it would be interesting to dig into the particulars of the piston rings and bearings used in these over-the-top applications to gain an understanding of what these components are exposed to during a gut-wrenching 4.5-second blast down a quarter-mile stretch.

(photo by author)


These engines, limited to 500 CID, basically operate in the 8,400 to 8,500 RPM range during the entire run, utilizing a slipper clutch system that allows engine tuning within this very narrow RPM band. Engine configuration is loosely based on the Chrysler 426 Hemi format with a 90-degree cylinder angle, two valves per cylinder and hemispherical combustion chambers. Bore is at 4.19″ and stroke is at 4.500″ (combos may vary). Blocks are machined alloy forgings with ductile iron cylinder liners. These engines run “dry” with no liquid coolant. The absence of water passages result in increased block strength with the need to add a block “filler” for added rigidity. Cylinder heads are also CNC machined from alloy stock, fitted with two spark plug ports per cylinder, titanium intake valves and solid Nimonic 80A exhaust valves. Intake valves are approximately 2.45″ in diameter, with exhaust valves at around 1.925″. The valvetrain includes a billet steel camshaft, solid roller lifters and full-roller rockers, titanium valve springs and retainers. Crankshafts are billet steel, fitted with five bearing shells. Connecting rods are forged alloy. Pistons are forge alloy, with a three-ring package. Piston grooves are hard-anodized to prevent microwelding. Piston pins are secured with alloy pin buttons to aid in quick piston changeovers.
The supercharger is a 14-71 type roots unit, driven by a cogged belt. About 45.5 PSI boost occurs at wide-open-throttle. The engine oiling system is a wet sump setup with a capacity of about 16 quarts. Oil pressure is about 200 lbs. cold and about 160 lbs. during a run. The fuel mixture is primarily nitromethane, with about 15% methanol. Nitromethane features a high oxygen content, which means less air is required for combustion. Very rich mixtures are tuned. Coupled with nitromethane’s ability to absorb heat as it vaporizes, this helps to promote engine cooling. In other words, these engines run on tons of fuel and little air (instead of “conventional” 14.7:1 air/fuel, mixtures can be as great as 2:1). Fuel consumption is about 1 gallon per second. Whoof.


Here’s another view of a top ring’s plasma facing damage from the same engine.

Cylinder pressures are incredibly high, as much as 12,000 to 13,000 PSI (when detonation takes place, cylinder pressure is in the 16,000 PSI range). To put that into perspective, a Pro Stock engine may generate around 4,000 PSI of cylinder pressure. This is a major factor when considering the abuse experienced by the rings and bearings.

(photo by author)


To find out what’s happening in the Top Fuel ring arena, we spoke with Clevite’s Don Sitter and Federal-Mogul’s Scott Gabrielson, each of whom work hand-in-hand with teams in developing packages that perform.
According to Sitter, Clevite offers a hardened ductile iron top ring (their PC479 material, tradenamed Firepower). This ring is also available with a moly face, but Sitter noted that some builders prefer not to use the moly since firing pressures in detonation instances can sometimes cause the moly to chip off, potentially contaminating the oil filter.


The second ring from the same engine features an inner chamfer.
“There are two schools of thought with regard to top ring size,” noted Sitter. “We introduced a 0.078″ axial height ring with a 0.017″ Dykes step. Prior to that the most common top ring was a 1/16″ Dykes-style ring with a 0.017″ step. In working with various teams, we found that distortional effects caused the 1/16″ ring to reduce twist, essentially turning the ring into a beveled washer. It was obvious that substantial compression was getting past the top ring. To fight that, we went to the thicker ring, which worked out very well. A favorite saying of one of the Top Fuel builders we work with is ‘mass saves your ass,’ which was certainly true in this case. We also changed the second ring to a 0.078″ moly-faced version with a barrel (radius) face.
“Considering the other variables involved, however, you can’t look at the rings as a stand-alone of the overall equation,” Sitter said. “You must also consider cylinder finish, as some builders run a 280 finish followed by a plateau finish, while others go with an as-cut 280 or 400 wall finish. There are substantial differences in the tuning of these engines, including blower overspeed, static compression, amount of fuel delivery, timing, clutch management, etc. One team may have problems with pan pressure and sealing, and by switching to dual Dykes (the Dykes ring has a dam cut about a third of the way across the radial wall, which allows pressure to get behind the ring and push it against the cylinder wall), but the same deal might not work for another team.
“Top ring gap will range, depending on the builder’s experience, from as tight as 0.028″ to as much as 0.044″. The enormous heat generated during combustion necessitates these larger gaps.


Heads and piston/rod sets are removed after every run. Rings and rod bearings are always replaced after every run. To save time, some teams replace the entire piston/rod/ring/bearing set. After examination, pistons and rods may be reusable.
(photo courtesy Clevite)


Oil is also replaced after every engine shut-down, due to the excessive nitromethane fuel wash.
(photo courtesy Clevite)

“Some crew chiefs have told me that when we went to the thicker rings, pistons ran cooler due to the decreased thermal resistance in a dry block,” Sitter said
Sitter noted that taper-faced second rings, regardless of material, tend not to be effective because any compression that leaks past the top ring will load the face of the taper ring, causing the ring to be pushed away from the cylinder wall, increasing blowby and pan pressure. A barrel-faced ring fights this because the tangent point is closer to the top of the ring. Sitter also noted that Clevite is introducing a new second ring in 2007, a reduced radial wall 0.078″ barrel-faced ring positive twist ring. This prevents the second groove from undercutting the top groove, allowing the No. 2 land to better withstand the primary firing pressure at the top ring. The reduced radial wall will also help to bring the mass back to close that of the original 1/16″ barrel ring.
“The laws of physics are routinely being broken in Top Fuel,” jokingly noted Federal-Mogul’s Gabrielson. “What these teams are accomplishing is nothing short of incredible.”
“Dykes rings seem to work very well in supercharged applications,” Gabrielson said. In the beginning, top ring materials were generally chrome plated stainless steel, but about 15 years ago this progressed to the use of ductile iron with a plasma moly face. Stainless tends not to be very compatible, with the chrome plate tearing up cylinder walls quicker. Granted, the cylinder liners are replaceable, but since the teams have only about 75 minutes to service the engine between rounds, if a wall goes away, the team will usually just swap out the entire block to save time.
“The most common top and second ring sizes have been 1/16″. Our experience has been that some crew chiefs have used Dykes second rings in place of rectangular rings, but with mixed results,” Gabrielson said. Some experimentation with wider Dykes rings (5/64″ face) has taken place, with results showing superior resistance to twisting. We’ve seen mixed reviews with regard to the wider rings, with some teams claiming improvements and others saying that they saw no change. Top rings simply don’t last, and are usually destroyed during the run, so ductile iron plasma-faced second rings are the norm, since you need a durable backup ring. Ring fracture isn’t a big issue, since the incredible cylinder pressure seats the ring on the bottom of the groove, eliminating flutter. The top ring simply fails due to pressure and heat, leaving the second ring to serve as the essential backup compression ring.”
Oil rings, because of the pressure formed around the expander, can actually be smashed. Regardless of the brand, style or type of material, rings don’t make it through more than one run, so they’re replaced as a matter of course between rounds.

tf10Detonation events will damage main bearings as well. These mains were exposed to a single run. Note the severe scoring, the result of enormous forces created by the astronomical cylinder pressures.
(photo courtesy Clevite)

tf091Here are three upper rod bearings that experienced a single run. Note the extrusion of material, which is especially evident in the center shell seen here.
(photo courtesy Clevite)

tf08Wet sump oil systems are a must due to the need to change contaminated oil quickly.
(photo courtesy Clevite)


“While rod bearings haven’t changed much in the last eight years,” noted Clevite’s Sitter, “there was a series of changes in 2004 involving NHRA-mandated reduction of nitro, blower overspeed, etc., in an effort to regulate speed (since speeds were approaching 330 MPH). It’s taken two seasons to get back to performance levels of 90% nitro. Now, we see more detonation and more damage to upper rod bearings. Again, because of the incredible cylinder pressures, upper rod bearings actually begin to extrude (about 0.080″ at the ends), making them appear as flanged bearings. If materials change, moving to a mild grade steel, for instance, this would still present a liability to the crankshaft, since the harder extrusion would get into the journal fillet, possibly creating a stress area. At the present time, Top Fuel crankshafts are generally changed out anywhere from three to five runs (some teams stretch this to as many as 12 runs). Since these crankshafts cost around $3,500 each, and since the team may make about 200 passes each year, the difference between buying 20 cranks versus 60 cranks per year would present a real financial problem.
“A number of detonation management issues need to be addressed before we blindly change rod bearing design,” Sitter said. “The problem isn’t the bearing … rather, it’s how the bearing is being treated. One analogy is that rod bearings can be viewed as the circuit breakers in the system.”
“Rod bearing clearances have decreased,” Sitter said. “Years ago, it was not uncommon to see rod bearing clearances in the 0.005-0.006″ range, with main bearings in the double digits. Today, rod bearing clearances range from 0.0035-0.0045″, and main bearing clearances are in the area of 0.0045-0.006″.”
“Typically, Top Fuel bearings are not coated with a special anti-friction treatment.,” Sitter said. We’ve tried Tri-armor, but there does not seem to be any big advantage. They work as expected, but don’t offer the kind of benefits you need in a Top Fuel application. The issue focuses more on how to prevent the engine from shedding parts when detonation occurs. Our V bearing works great.

This is constructed of lead indium plated overlay on a cast tri-metal lining with a conventional steel backing. This does a good job of managing the detonation environment. While the moly coatings, such as our Tri-armor treatment, survive very well, this offers no particular margin with regard to detonation events.
“Top Fuel applications experienced thrust bearing problems a few years ago, which prompted us to make several improvements to the flanges, including the use of lead indium on the thrust faces, and to work with teams and crank manufacturers with regard to thrust face surface finish,” Sitter said. “We did note that those teams having thrust bearing problems were all using a particular oil, which convinced me that some oil brands do perform better than others.”
By the way, most teams run 70-90 W synthetic oil. It’s interesting to note that because of the excessive nitro fuel wash that runs through the engine, fuel dilution of the oil is so great that the engine oil must be changed every time the engine is shut off (even following a warm-up). As noted earlier, since these are dry engines with no liquid cooling system, this excessive fuel wash helps to manage temperatures, basically preventing the pistons, heads and valves from melting.
The incredible cylinder pressures are so great that it’s not at all uncommon for hefty wrist pins to bend. In addition, rod small ends are elongated and rod big end saddles can be pulled out. When you consider their environment, it seems a miracle that any rings or bearings can function and allow these engines to perform their jobs, yet they do, weekend after weekend, all year long.
By the way: ever notice that the exhaust tubes are always turned up, with exhaust pulses exiting upwards? This isn’t just for appearance. This is due to the enormous cylinder pressures. By directing the exhaust upwards, this helps to generate greater chassis downforce for better tire bite and stability. If the tubes aimed downward, the business-end of the car might very well be lifted off of the track surface.

Typical burnout to transform the tire surface to a low-durometer, sticky state for increased traction.
(photo courtesy Clevite)


These engines are typically not fully assembled or dyno’d in the shop. Rather, they’re assembled in the car. Each run include fresh rings, rod bearings, and oil.
(photo courtesy Clevite)


Gone in about 4.5 seconds, currently reaching a trap speed of around 330 MPH.
(photo courtesy Clevite)

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