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cracked exhaust manifold

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Old 02-20-2011, 08:11 PM
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Exclamation cracked exhaust manifold

im new to this forum and i am in need of some help. I bought a 91 wellcraft nova with twin 350 mercs just junder 27 feet long. i bought this boat at an auction as a non runner. I was able to get both engine running in one weekend. while i was working on the engines i noticed that all the exhaust manifolds have about a three inch crack in them and all in the same spot. i think its because the engine werent winterized, i live in MI and it does get very cold here. i wondering if these engine blocks are know to cracking if water freezes in them. i paid 5k for the boat with trailer, not sure if its a good deal or not but i fell in love with the boat and looked liked a fun toy. im just looking for some insite or if theres certin areas i should be looking at on the blocks. i didnt see an oil leaks, i ran them for a secound with the hose hooked up but no water was flowing through due to the cracked manifold i think. any help would be great. thank you
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Old 02-20-2011, 08:20 PM
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one tell tale on cracked blocks is to pull the dip stick and if the oil level appears to be a few inches above the full line there most liklely cracked although this is something that would need to be checked before anything was done to the engines. If you do need engines and are looking at cost affective options grab one of those free Auto-RV traders we have in our area here and look in the repairables section there is usually a half page ad for a place called Budget Rebuilders. I have used several small block remans from them and all have worked great.
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Old 02-20-2011, 08:21 PM
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the engines, oil coolers and exhaust are all cooled by water, there may be other cracks in other locations. The engine has freeze plugs that "hopefuly" pop out to prevent the block from cracking. Is there water in the oil?? you will have to run the engines and see if water is leaking from other location. Sounds like it wasn't winterized and that why you have the problem.
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Old 02-20-2011, 08:25 PM
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the exhaust manifolds are cooled last before water exits the boat, if you have water coming from there, the block is getting water in it too, check the oil, if it don't look contaminated with water or overfull, run the engines and then look for leaks, and check for oil, if the blocks are cracked, it can leak out or it can leak into the oil. There will be signs in the oil if its getting in there.
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Old 02-20-2011, 08:38 PM
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thank you to all that got back to me so fast. i have run the engines, the oil didnt look milky or over filled. i want to buy two sets of manifolds wich as we all know arent cheap and run it. i just hate to buy them and have block issues. have any of you had cracked exhaust manifolds and had no block issues??
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Old 02-21-2011, 03:09 AM
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Small blocks I have found like to crack about an inch below head mating surface on the outside take flashlight & maybe a mirror see if you see a horizontal crack anywhere. A lot of times I have had to back the boat in the water & get full flow before it leaks but if it is there it will leak.
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Old 02-21-2011, 07:47 AM
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Another way to check for cracks elsewhere is to rig up a pressure manifold with an air chuck, ball valve, and a guage. If you have any other leakage in the cooling jackets it will instantly loose pressure and you should be able to hear the air bleeding off in the general vicinity of the crack. DONT! go over 20 psi. otherwise you will start blowing gaskets.

I have two sets of good used cast iron freshwater SBC exhauts if your interested.
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Old 02-21-2011, 07:54 AM
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If you think manifolds aren't cheap......look into marine headers. Manifolds will look like a bargain after that.
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Old 02-21-2011, 09:54 AM
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I have a set of stock manifolds, and a set of headers and risers for a small block that i will be putting in teh sawp shop sometime soon. I hate to say it, though, it sounds like the problem may be bigger than that.
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Old 02-21-2011, 11:11 AM
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Ouch. I am so sorry. Sounds like you have some work to do and some money to spend...
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