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MGB Crank doesnt turn freely - new main brgs


Senior Member
boggsy, I have just restored a"T "engine and I found the crank locked up on tightening the big ends and also the mains I double checked the crank journals and big ends for size they were perfect , checked they had the correct markings on the under size slippers, these were also correct. so I tried each big end and found they locked up, the mains were the same. What had transpired with a previous owner/mechanic had files the caps to tighten the clearance for the existing wear, so when the journals were brought back to a standard the con-rod and main bearing journals were now undersized, Had the mains reline bored to original size, the big ends were also resized , checked clearances of each journal, all ok, engine now turn over very sweetly Hope this is not your problem . I have been told it was a common practice with older engines. Saltiga


Jedi Hopeful
Lots of good comments: Update: I checked the ring gaps and all appear correct. My bore is .010 over and checked out at 3.168 or so with a simple calipers. I don't have a bore gauge handy or snap gauge but think it is correctly .010 over (should then be 3.17). Using a rule of thumb of .0035 inch gap for each inch of bore I came up with about 11 thou gap. I checked the compression rings and the first (lowest) ring is right at 11, the upper ring is 14 or 15 thou. This seems right to me from reading a chevy 350 website discussing rings and competition compression. There is stated that the first ring should have a tighter gap than the second. In any event no filing of the rings necessary in my case.
The crank does turn OK now, will not coast but will turn freely and smoothly. This my main issue was using 30weight oil instead of assembly lube on the main bearings (I later used proper assembly lube) and as I tightened all the caps it loosened up. I was told that the bearings are not fully spherical until compressed. Seems to be logical and this incident seems to back that up?
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