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I just bought a complete gen 5 502 HO for $900, it has the right heads and a complete tpi manifold. I ran the compression and was happy with 125 at 7k feet. Now the question. Does mercruiser drill through the siamesed part of the bore barrels to help cooling. There are 4, 1/8 pipe plugs about .5 inches above each freeze plug on each bank. They are not crack repairs. I was told by a local machine shop that Mercruiser did this on their Marine 502s for cooling issues. Sorry I can't post a pic.
 

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Discussion Starter #6 (Edited)
:shock::duh:
It is not a shop I deal with, but they are pretty reputable around here. I did pull one of the plugs and it looks like there are holes drilled right through the barrells just below the deck exactically as was described to me. Maybe they like to put them high since that would be the hottest area of the cylinder or to to help the air get through or something in a lake enviroment. There are two of these engines (twins) and they have the same ASM intakes, AN oil cooler lines and drilled cylinder barrels.
 

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I just got done rebuilding my GEN V and no holes. There is no reason to drill out the Siamese. Darts Big M blocks are not drilled and they all run great. Sound odd to me.


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I just bought a complete gen 5 502 HO for $900. Now the question. Does mercruiser drill through the siamesed part of the bore barrels to help cooling.
No they don't.

I was told by a local machine shop that Mercruiser did this on their Marine 502s for cooling issues .
There are no cooling issues with the 502's in any of the generations.


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Someone did this mod or repair for a reason. It would be interesting to find out why.

Only cooling mods that involve drilling any of the blocks are usually with the headgasket and block deck.
 
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