The Stovebolt Site Forums The Shop Area Engine Shop Main Bearing Bore Diameter - 292

For a Chevrolet 292, what is the main bearing bore diameter in the block (without bearings installed)? And what is the tolerance for being out of round?

The measurement I’m getting using a mic and dial bore gauge is 2.4905” straight up and down (90 degrees away from the cap parting line) But very near the parting line the bore is .0020” larger which seems like a lot. Hoping to avoid a line bore or hone. Thanks.

The Federal Mogul shop specification catalog #115 lists the main bore as 2.4906"-2.4916". Yes, it needs to be round, within those specifications. Are the mating surfaces perfectly clean, and are the bolts torqued while taking the measurements? Side to side dimensions aren't as critical as top to bottom, but a .002" difference is pretty extreme. I usually ignore the dimension at the parting line and rely on a vertical measurement, and one at 45 degrees from vertical both ways. If those are within tolerance, press on!
Jerry

Thanks for looking up those dimensions. The surfaces are cleaned and torqued to 65 ft lbs. I’ll check them again as you described. I’m hoping to not need a line bore or hone.

Be very careful when selecting a machine shop if you do decide to line bore the engine. Gear-drive camshafts can be incredibly critical on timing gear fitting, and the usual procedure of taking out equal amounts in the block and bearing caps can result in gear teeth bottoming out. I usually set up my portable line bore rig to barely scratch the block, and take the majority of the cut out of the bearing caps after shortening them about .010". Yes, I have that equipment.
Jerry