[Dave in MN]

Post #29: The engine has inserts. If the engine has aluminum insert bearings, lack of oil at the rear main bearing will lock the engine up as you described. I rebuild engines and after locking up a higher output engine I was building for myself, on a break-in stand a number of years back, I ran some tests on the insert bearings and the clearances needed.

From my experience with stock gravity oiling, to be trouble and leak free, the rear main clearance needs to be between .0018" - .0022". My methods of measuring, assembly and choice of lubricants likely make/made a difference during the tests.

I used the same engine that locked up for the tests using the same assembly lube, methods of measurement and thrust clearances. I only changed the insert bearing clearance to the main journals. I then ran the engine with a heavy dyno load on the fresh bearings. With too little rear main clearance the aluminum bearing material would weld itself to the journal. Upon teardown, the insert could be removed with a brass punch and the remaining aluminum stuck to the journal could be removed with an acid brushing. the journal was not destroyed.

Terry, It will be interesting to see what you find when you open it up. Please keep us posted.