Setting the tone for your build begins with starting out on the right track. Overlooking steps and taking shortcuts are no way to piece together an engine; regardless if it's for the street or strip. While it may seem like parts fly off shelves and magically compose themselves into engines, they don't. There are codes of conduct that must be followed like preplanning and measuring essential dimensions such as the crank journals, main bearing tolerances, and crankshaft endplay. To ensure the bearings have adequate clearance to maintain oil pressure, this crucial process can't be passed up. In either situation, it's a recipe for disaster if it's neglected. By simply checking these items ahead of time, you can prevent a full-blown meltdown, not to mention some serious pocket digging and downtime should things go bad.
To do the job you'll need some tools of the trade, but the good news is it only takes a little know-how to get the job done. To help clarify why checking the clearances is important, a bearing with too little clearance can build heat quickly under extreme loads of the crankshaft and eventually burn the bearings out. On the other hand, too much clearance between the bearings and crank journals will not create enough oil pressure which, in turn, will starve the engine of lubrication.
To showcase our efforts, we jumped on board with Quarter Mile Performance in Chatsworth, California, where Michael Consolo was piecing together one of his personal mills, a 410ci race only small-block that's destined for the strip. While this isn't a typical street motor designed for stop-and-go traffic, the methods shown here are applicable for all combinations. If you lack the tools to get this particular job done, your local engine shop should be able to offer these services; that means do it once and do it right.
Quick Notes
What We Did
Checked the main bearing clearance on a 410ci small-block
Bottom Line
Basic engine building fundamentals can go a long way
How Long It Took
Two hours
QMP recommends taking measurements...
QMP recommends taking measurements from four areas of the journal. On a bench, Consolo began by measuring each leading edge of the journal and then rotated the crank 90-degrees to record the additional two. This technique ensures journal roundness of the crankshaft. Note: the crank should be prechecked for straightness and balanced before this procedure is performed.
Our journal measurements revealed...
Our journal measurements revealed 2.4484 inches; the numbers can be added to the setting fixture for the bore gauge. The gauge is then zeroed out and is ready to be placed into each main bore.
Next, Consolo installed each...
Next, Consolo installed each bearing into the block. The bearings with holes insert into the block side for each oil galley. The other half of the bearings install into each cap (tang to tang). Depending on the year of the block and crankshaft, at this point, the rear main seal can be installed.
Consolo then torqued each...
Consolo then torqued each cap according to the bolt manufacturer's instructions. In this case, we placed moly-lube on the threads and shoulder of each bolt and locked them down with 65 ft-lb.
While measuring the bearings,...
While measuring the bearings, any variation in the measurements can create a bit of confusion. QMP's method includes measuring the clearance of each bearing vertically, before and after the oil galley hole. For each bearing, the gauge read between 0.0032 and 0.0034 inch.
Consolo then loosened and...
Consolo then loosened and removed each cap. Adding oil to the upper and lower bearings will prevent any dry galling once the crank is spun. The crankshaft was then lowered into the block. QMP installed the crank with the front counterweight facing up in order to precheck crankshaft endplay.
To check crankshaft endplay,...
To check crankshaft endplay, the last cap was tightened to register the cap into the block and then broken loose. With a micrometer at the front of the block, Consolo used a flat-blade screwdriver between the cap and counterweight to shift the crankshaft from front to back. We recorded 0.0008-inch of endplay. Note: shifting the crank back and forth will also set the rear main cap since this particular block lacks dowel pins.
To ensure everything was correct,...
To ensure everything was correct, the rear main cap was torqued to 65 ft-lb and rechecked again at 0.0008-inch. We were good to go for a final torquing sequence.
Our final step included torquing...
Our final step included torquing each cap to the recommended specs. At this point, the crank should spin freely with minimal effort, without binding or running into tight spots. That's it-bring on the rods and pistons.