1 piece vs. 2 piece rear main

I had an engine in my 1985 gmc Sierra with the classic 2 piece rear main that broke the crankshaft and ruined the block. I got another block, but it is a later style with the 1 piece rear main. My question is, what all will work from my old engine on this one? I got the short block so I have crank, rods, oil pan, and even a flywheel. Will the starter off the other engine still work? Thanks


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You can physically replace one shortblock w/the other. The original heads and intake, accessories and brackets all will fit, etc., but there are some things to consider:

The oil pans are different, as is the flex/flywheel but you got the flywheel so that's not a problem. There could be a difference in the pistons as far as dish or valve relief volumes go, so the compression could be effected.

If the new engine is a roller cam set up the distributor gear has to be melonized. If the 1-piece shortblock has the plastic timing cover, they don't interchange w/o some modifications but if the cover is there you are good to go.

No problem w/the starter working- IF the diameter of the flywheels are the same. There may or may not be a provision for a mechanical fuel pump- check to be sure the machining is complete if you need to use one, otherwise you'll need an electric fuel pump.

The newer engine has the standard steel timing cover and appears to be machined to accomodate a mechanical fuel pump, however it did have a block-off plate on it. It had a flat tappet cam in it, so im guessing its a 86-88 engine, though i havent ran the casting #s yet. I havent measured the flywheels but i was just wondering since some people say the starter will work and some say it wont.

I'd say your guess on the engine being around '86-'88 will be close. The date code and casting number are both back by the bell housing ledge.

FWIW my '92 TBI truck engine c/n 10054727 has no provisions for a roller cam, but it lacks the machining for the mechanical fuel pump. For future reference, THIS thread has a list of roller and non roller '86-up blocks. Might not be all-inclusive.