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GT40 Engine Rebuild - Quick Help

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nautique_wake View Drop Down
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    Posted: October-14-2017 at 2:43am
I had posted here before and received some good information, but I never pinpointed the exhaust cause of my engine failure. I ended up ordering a new 351 with gt40 heads from ATK marine, but still want to determine what happened to the old engine.

Some quick info, boat shut down running across the lake, developed a knocking sound, thought it was a leaky exhaust manifold gaskets, install new gaskets, sound got less, but still something not right,. I ended up doing compression test, the 2nd cylinder from front of engine on port side had no compression, had mechanic remove heads and cylinder was trashed.

Oil was never milky, if that is the case, is the only way water could get back into the cylinder be a crack/leak in the exhaust manifolds? Or was leaking from the connection between manifold and riser? Is there any particular reason it would run into that particular cylinder over another?

I have attached photos of the exhaust manifold on the side of the engine. I am going to replace them anyway, but want to make sure I am not missing something.

Thanks in advance



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KENO View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: October-14-2017 at 11:03am
You could also have a crack in the cylinder head above the intake and/or exhaust valves that can't be seen unless you remove the 2 valves and inspect that area.

A leak there lets water from the water jacket into the cylinder

That'll put water into the cylinder and it won't get to the oil immediately, just like water from an exhaust manifold leak won't get into the oil immediately.

In both cases it has to leak by the rings to get to the oil pan.

So pull those 2 valves and look for a crack.

It could have been a bad head gasket or warped head or block from an overheat letting water into one cylinder as well

It sounds like you're putting new manifolds and risers on and you have a whole new engine, so your problem should be gone but that's an ugly looking cylinder that had more than a water issue going on.

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gun-driver View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gun-driver Quote  Post ReplyReply Direct Link To This Post Posted: October-14-2017 at 1:19pm
The manifold and riser look about normal. That’s not to say isn’t cracked but before I spent money on new ones I would find out if that was or wasn’t the problem.
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nautique_wake View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote nautique_wake Quote  Post ReplyReply Direct Link To This Post Posted: October-14-2017 at 1:40pm
Thanks for info, I am just super paranoid and I don't want to damage the new engine.

I would love to save the money, but I am going to go ahead and replace the manifolds and risers.   I believe to have a valid warranty I need to anyway and I would be literally sick if they caused the problem again.

I just wanted to make sure I am not overlooking anything that could have caused this that would not come with the new long block.

Anyone know where the best price on new manifolds and risers?   



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