Subscribe to Precision Engine
Sign up for our E-newsletterPROJECT 632, PART 3
SHORTBLOCK ASSEMBLY
Our shafts rotate and the slugs run up ‘n down. Life is good.
by Mike Mavrigian
photos by author
Clevite 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.
GRIND RODS FOR CAM CLEARANCE
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.
GRIND BLOCK FOR ROD CLEARANCE
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.
Tags: BALANCING, CRANE, DART, GRIND BLOCK FOR ROD CLEARANCE, GRIND RODS FOR CAM CLEARANCE, LUNATI, MAIN BEARINGS
