502 head gasket question
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502 head gasket question

  1. #1
    Senior Member namba860's Avatar
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    Default 502 head gasket question

    Anyone know if the Mark 4 head gasket is any different then the Mark 5 or 6 head gasket? Take a look at the pics cyl. #4 piston melted. look at the gasket the engine builder used on it and how it is blocking the water cooling hole and how the other pics show they are unblocked. This is a mark 4 502 bbc original M.ercruiser engine
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    Last edited by namba860; 03-22-2017 at 08:53 AM.

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    Some guy obnoxious001's Avatar
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    Some overlap of that hole is not uncommon with many big block head gaskets. I believe the main water flow runs through block to the rear of the engine and through large openings into the head, back towards the front of the engine. That overlap used to make me do a double take as well, but don't think it would necessarily be the cause of your problem

    17048 Fel Pro is listed as a marine Gen 6 gasket, 4.540" bore. I don't think I have one of those here to lay over a MK IV specific gasket to compare.

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    Senior Member namba860's Avatar
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    I ordered an original Mercuiser gen 4 head gasket to lay over the deck and see. I got the piston out and the wrist pin is beat out of it so Im going to assume detonation. The plugs have good color so I know it wasnt lean. I just find it awfully coincidental that the piston melted next to that restricted hole.

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  6. #4
    Some guy obnoxious001's Avatar
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    Quote Originally Posted by namba860 View Post
    I ordered an original Mercuiser gen 4 head gasket to lay over the deck and see. I got the piston out and the wrist pin is beat out of it so Im going to assume detonation. The plugs have good color so I know it wasnt lean. I just find it awfully coincidental that the piston melted next to that restricted hole.
    While I understand your logic, I have to fall back on all of the hundreds of engines I have seen and put together. The "stock" Fel Pro 8180 type gaskets that come in the basic gasket sets don't even have those bypass holes in them. Yours while partially obstructed should still provide a large volume of water passing into the head, and as previously mentioned, much of the flow through the block will be front to rear.

    I went out to my garage and found that I do have a new set of 17048's, and the holes with the exception of the bore match up with a 17040, which is a marine gasket that fits 454 blocks. I also found some 8180's that came off of running engines, that have that hole entirely blocked.

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    I seem to recall many years ago reading Fel Pro explanation of that partially blocked hole, but why not call them and ask?
    Last edited by obnoxious001; 03-22-2017 at 12:50 PM.

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    I just now put a set of Cometic MLS Head gaskets on a Gen 4 Bowtie..one hole was half covered...there must be a reason

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    to keep more water flowing to rear of head?
    1990 ultra 21' open bow. 509, American turbine Jet

  9. #7
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    # 4 was detonating,you can see the melted aluminum from the piston.is this an mpi engine?

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