ENGINE HELP!! 1978 GM 305 OMC switched with 1987 GM 305 truck block????

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Paramedic2244

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Joined
May 22, 2012
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2
i have a 1978 thundercraft that has a 305 in it with OMC drive. The original block has a crack in cylinder 5. I bought an 87 GM truck 305 block, bored out at 40 over and planned to swap. When i went to put the flywheel from the 78 engine the flywheel hole mount is much larger and the bolts do not line up, subsequently the tourque coupler also does not line up of fit in the flange. What are my options as swapping the crank is not an option either do to rear seal?
 
Howard Sterndrive

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
Re: ENGINE HELP!! 1978 GM 305 OMC switched with 1987 GM 305 truck block????

your only option is get a different engine. Unfortunately, you missed by mere months. You need a small block Chevy made before the change to the 1 pc rear main seal, which occurred in mid 1987.
The only other option is a new or used GM parts crate 350/290HP - one of the ones made in Mexico from about 1999 to present as they still use the 2 pc rear main seal design block and crank.
There is no coupler to correct the mismatch you're dealing with now.
 
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