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Old 03-25-2012, 12:25 PM
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IROC_385z IROC_385z is offline
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Mercruiser/Chevy 230/250 questions

Hi all,

Seems to me like info for these old I6 motors is much harder to find out there than for the SBCs that I'm used to working with, so I'm hoping I can get some of the technical info from somebody here.

The story goes, my dad picked up a 1966 Pennyan with a Merc 230 for super cheap last summer. The stingers look good so we are moving forward on the next phase and deciding what to do with the engine. Knowing this WILL end up being a can of worms type operation, I want to get as well informed as possible before cracking the lid.

I *could* just run as-is and hope for the best, but I would really *HATE* to get 15 miles out onto Lake Erie when I notice the rod knock begin or whatever. That's why I want to just give it an overhaul now, but I need to figure out what to do.

Step 1 is going to be take it all to the shop to assure that the block/rods/head/crank are all happy. If the crank needs any work I think I will just get a 250 crank to stroke it while I'm at it. Cost of the rebuild is the same, otherwise, so why not?

Regardless of whether I stroke it or not, I would like to get the CR up to 9.5ish vs the 8.5 that these apparently run. Obviously the increase in stroke would accomplish much of that for me, but I like to do the math first so I know exactly what all needs to happen. That being said, does anybody here know all of the specs on these motors, in terms of determining CR?

I've found so far the bore/stroke, compression heights, rod lengths and CR, but I cannot find information on the deck heights for these blocks or the CCs of the heads. From what I can tell I have little doubt those two things change between the 230 and 250s, seems like the only diffs between them is the stroke and piston design. I know how to do the math, I just need these last two variables to plugin.

Can anybody confirm/deny what I have figured out so far, as well as to help me with the DH and CCs?

Lastly, this is a pretty old motor and I'm wondering if the seats will require the use of lead or not. I found a site with info on Mercruiser engines and it told me NO, but I am hoping somebody can confirm/deny from experience.

Thanks a bunch guys!
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