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Old 07-24-2014, 09:36 PM   #1
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Default Engine problem/no compression on 2 cylinders (merc 5.7 2002 250hp)

Hi All,

While attempting to enjoy my last weekend I've started hearing some unusual knocking noise from the engine compartment. Later realized that engine was very rough on idle. When made it to my destination port (45 miles away from my home port) i found one of the local mechanic and let him look at it. He did compression test on the spot. No compression on cylinder 1 and 4. I left the boat with him to investigate problem. He called me back saying that 2 of the valves got pulled into the head and one of them is really deep. His first idea was to get me new long block for 6.5k which I was shocked with. Got really upset. Looking for other solutions he send out heads to machine shop and they said that they are fixable. Newest scenario is to remachine heads with all new stainless steel valves etc for 3.5k inkling all the labor etc. I wanted to ask you why something like this could happen? I was taking care of the boat since I bought it 2 years ago and engine had only 320 hours. Also do you have any ideas of different route as far of the repair? I asked people around and mechanic got a good reputation in the area. Does his pricing and idea to fix it makes sense? Thanks in advance!
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Old 07-24-2014, 09:50 PM   #2
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Here's the video. Not sure if you can hear the unusual sound.

http://youtu.be/jGvzKu6Nbwg
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Old 07-25-2014, 01:44 AM   #3
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Tulip valves. The valve seat got so hot they deformed. Exhaust valves?

1 and 4 are on opposite sides of the engine.

This happens when exhaust gases get too hot, I know of two reasons this can happen.
First is burning water from water getting into the cylinder.
Second is ethanol gas that has gone bad or too much water absorption.
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Old 07-25-2014, 02:55 AM   #4
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[QUOTE=mmwjr;33909]Tulip valves. The valve seat got so hot they deformed. Exhaust valves?

Wow. I have seen that condition and never realized what caused it.

With that kind of heat, maybe you should rethink the long block option. I understand it is a lot of money...but you would hate to drop the 3.5k....only to find more damage on startup......

And you get a new engine out of it.....
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Old 07-25-2014, 03:28 AM   #5
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I think they were exhaust valves. I'll ask my mechanic. Whats bizarre is that the engine didn't overheated. The temp gauge was fine. When I checked the manifolds the starboard side seamed to be hot (definitely hotter then the other). Mechanic said the block looks almost perfect but he couldn't guarantee if there's no damage there. If the temp gauge was ok do you think I might still have the problem with the block? The engine run perfect before. Is it possible I could get bad gas on gas station which could cause the damage?
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Old 07-25-2014, 03:32 AM   #6
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I forgot to mention that the engine was still starting without the problem and running when we put it apart.
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Old 07-25-2014, 11:39 AM   #7
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Any lower damage would start with the pistons. Pull the heads and inspect the piston surfaces for missing metal. If they look good then I would expect the block to be ok.

My second boat had this happen, bought it knowing it was this way. One piston had 1/4 of it's surface eaten into.
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Old 07-25-2014, 12:51 PM   #8
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Thanks Mike. My mechanic said that the cylinders and pistons looked good with exception of one small scoring. He said it's 99% perfect so can't really justify spending additional 3k for new block. Also the route I'm going with stainless steel valves should prevent something similar in the future.
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Old 07-25-2014, 04:01 PM   #9
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First I think it is the valve seat in the head cast that yielded and not so much the valve failing. Second while SS are better using the word prevent is pushing the boat Gods around as under the right conditions anything will fail.

B.O.A.T. (Break Out Another Thousand) Gods love to prove this point over and over.
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Old 07-26-2014, 03:22 PM   #10
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Quote:
Originally Posted by mmwjr View Post
B.O.A.T. (Break Out Another Thousand) Gods love to prove this point over and over.
No truer words were ever spoken
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