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Head


Marvin Gardens

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I have a 1991 Malibu Sunsetter 201. Has 1100 hours, but under 200 on rebuilt Chevy 350. While searching for an oil leak Saturday I found water leaking from a 2" crack in the port head between cylinders 5 and 7. Is there any difference between a marine cylinder head and an automotive cylinder head?

The oil leak seems to be where the intake meets the head. Not much goop in rear of engine at the seem, quite a bit more at front and not leaking at front. It is spraying oil right at the blower fan.

What causes a crack in the head?

I bought this boat back in March. Previous owner told me about rebuild. He never mentioned cracked head. We've used boat all summer, I was disappointed with performance, but for our modest needs it was still fine. Now I see why performance was less than expected.

How bad job for a mechanic is this? Can I buy a local auto head? Any suggestions would be greatly appreciated.

Thanks

Gary

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I have a 1991 Malibu Sunsetter 201. Has 1100 hours, but under 200 on rebuilt Chevy 350. While searching for an oil leak Saturday I found water leaking from a 2" crack in the port head between cylinders 5 and 7. Is there any difference between a marine cylinder head and an automotive cylinder head?

The oil leak seems to be where the intake meets the head. Not much goop in rear of engine at the seem, quite a bit more at front and not leaking at front. It is spraying oil right at the blower fan.

What causes a crack in the head?

I bought this boat back in March. Previous owner told me about rebuild. He never mentioned cracked head. We've used boat all summer, I was disappointed with performance, but for our modest needs it was still fine. Now I see why performance was less than expected.

How bad job for a mechanic is this? Can I buy a local auto head? Any suggestions would be greatly appreciated.

Thanks

Gary

Hey,

The crack could be from the engine not being winterized correctly, there might of been water in the head that was not fully drain and then the water froze and expanded to the point of the metal breaking. I have seen this in a tractor that the farmer had replace the coolent and never added anti-freeze. Or the crack could be from a improper troquing head bolts, to tight to much pressure, to loose the head could be rattle and cose the crack, and for the head it could be replaced by on auto head provided it was the same style, some of the engine have full rollers and some have no rollers, or just a roller cam.

RAJKD1

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I have seen 5.7 chevy marine heads on e-bay, complete for $350 - $400. You would bolt them right on, meaning you would not have to do any work on them. There will be a part number somewhere on the casting of your cracked head. You can use that number to find the correct head to purchase. You may also want to check the the motor itself to see if it too is cracked. I was told by a chevy mechanic, when a chevy motor is not winterized properly and the remaining water freezes, the block is more proned to crack before the head would. The thickness of the water jacket in the block is thinner. He has seen engines that look like the head is cracked when it was actually the block or both. Just something to look for when you have it a part. And that is if your crack was caused by freezing.

Brian

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Just check with a local machine shop, or an auto parts store can order a rebuilt head from a regional machine shop. There will be a casting number by the valve springs. You will just need to remove a valve cover to see it. Maybe a pair of heads would be good, as if one cracked from freezing, maybe the other is "almost cracked". Also, take a good look at the block on the sides below the heads, above & below the freeze plugs for cracks. Also, when the intake manifold is off for the head replacement, look at the block inside, between the lifters & the surface that the head sits on. Sometimes they will break there too.

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  • 2 weeks later...
I have a 1991 Malibu Sunsetter 201. Has 1100 hours, but under 200 on rebuilt Chevy 350. While searching for an oil leak Saturday I found water leaking from a 2" crack in the port head between cylinders 5 and 7. Is there any difference between a marine cylinder head and an automotive cylinder head?

The oil leak seems to be where the intake meets the head. Not much goop in rear of engine at the seem, quite a bit more at front and not leaking at front. It is spraying oil right at the blower fan.

What causes a crack in the head?

I bought this boat back in March. Previous owner told me about rebuild. He never mentioned cracked head. We've used boat all summer, I was disappointed with performance, but for our modest needs it was still fine. Now I see why performance was less than expected.

How bad job for a mechanic is this? Can I buy a local auto head? Any suggestions would be greatly appreciated.

Thanks

Gary

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A automotive head would be fine for your application if the specs are the same (valve diameter, combustion chamber size etc.). You need to closely inspect the block for cracks also. Non winterized engines tend to crack the block where excessive engine temps tend to crack heads. Boats are no different in this area than autos. I suggest using known remanufactured heads not Cooter Brown specials. Replace both heads or at least have the other head inspected and freshened up.

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Just for curiosity sake has anyone ever welded a cracked head?? If they are cast iron, or aluminum for that matter cant they be welded? I have seen automotive heads welded if it was a small crack and it held up fine. Would there be any difference in doing this on a marine engine?? Otherwise, time for performance heads and more power.

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Yes, a cylinder head can be welded, but be cautious. No difference between marine and automotive. Performance heads for that application will make quite a difference in performance if you go that route.

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Blocks and heads have casting numbers, you can cross reference certain numbers that match, but if you can find the same casting you would be much better off that way you know you have the same year or close to manufacture date. The other option is to upgrade both heads and you can even go aftermarket with upgraded valves and springs Thumbup.gif may cost a bit more to buy a new set of heads, but locating a used head that is in great shape to match the one you have now may be a challenge.

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