330 SA Big Block Cylinder Head

P

Pinner58

New Member
Aug 23, 2016
13
Longport, NJ
Boat Info
1997 330 DA Sundancer, V-drivers,
Engines
7.4 Mercruisers MPI Blue
Need help, 1997 Sundance with the 7.4 mercruiser engines. 454 big block. Have an exhaust leak. I first tried that metal patch, but filling in the worn area but still having exhaust leak. Thinking of changing out the cylinder head. First I was told that I just need to match up the six digit number under the value cover, which I did. The issue is the one currently on the engine has a cast number of CM6 and the used one I found has the same six numbers but has CM4. What's the difference? Can I replace the cylinder head that I have with one that has marking of CM4. Did anyone else come across this
 
Pinner58 said:
Need help, 1997 Sundance with the 7.4 mercruiser engines. 454 big block. Have an exhaust leak. I first tried that metal patch, but filling in the worn area but still having exhaust leak. Thinking of changing out the cylinder head. First I was told that I just need to match up the six digit number under the value cover, which I did. The issue is the one currently on the engine has a cast number of CM6 and the used one I found has the same six numbers but has CM4. What's the difference? Can I replace the cylinder head that I have with one that has marking of CM4. Did anyone else come across this
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As long as they're the same casting number, you'll be fine. This of course is as long as someone didn't shave anything off or enlarge the valves. You don't want to have two different compression ratio heads on your motor. Bad...
 
I believe it's all stock. What would happen if the one was shaved a little
 
Just mill the exhaust surface on the old head. .030 taken off would be no big deal. The new head your considering would be a non issue with a small amount milled off to make it flat.
 
You want the heads to match. If you don't know how to measure heads, which is pretty tricky even for guys that know how, then you should bring both heads to a machine shop to have them checked out. You mill the surface that mates to the block. There's other times you need to mill the intake side, but rarely would you ever mill the exhaust side except to make sure it's flat. It wouldn't hurt, but unless it's warped, it's a complete waste of money and time. Where is the exhaust leak? Is it between the manifold and the head or the riser etc?
 
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Common problem on the Big block head exhaust surface to have corrosion, the gasket traps water and that's how it happens
 
Depending on how deep the damage is, scoflaw is correct, you can have it milled to correct the problem. If the head is in otherwise good condition, that's what I'd do. It won't cost very much to surface the exhaust side.
 
Pinner58 said:
Was able to pick one up for 150.00
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That's great. Gen VI 454s are great motors. The heads are tricky though because of the chamber shape. At least you don't have to worry about adjusting the push rods. You torque down the rockers and are done. I put studs on my street Gen VI 454 so I could run roller rockers. That one I need to adjust.

20180425_135638_39893957950_o.jpg
 
Well that's just the beginning. Needs to be stripped, check for cracks, measure ID. of valve guides and then a valve job. New springs as well .
 
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