4.3 mercruiser with burned exhaust valve.....what could cause this

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onebighead

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Good day. I have a 1995 Chaparral with 4.3 v6 GM. At the lake I experienced a severe power loss. Got home and performed compression test to find zero compression on #2 cylinder. Removed head and there it was, burned exhaust valve. I will replace it after touching up the seat, but what could cause this? I would like to find the cause and fix that also. thanks Lets hear some ideas
 
Bondo

Bondo

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

Monte Davis said:
Good day. I have a 1995 Chaparral with 4.3 v6 GM. At the lake I experienced a severe power loss. Got home and performed compression test to find zero compression on #2 cylinder. Removed head and there it was, burned exhaust valve. I will replace it after touching up the seat, but what could cause this? I would like to find the cause and fix that also. thanks Lets hear some ideas
Click to expand...

Ayuh,.... Check the contents of the fuel filter for water,...

Water don't burn, 'n sets up a Lean condition, inducin' the detonation that smoked yer valve...
 
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ricohman

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

Lots of things.
Lean mix
Valve not closing
Exhaust leaks at the head
Timing
Bad lifter
Carbon
And the list goes on. From what I have seen in the auto world the #1 spot goes to the valve being held open and hot exhaust burns away the valve.
 
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Stamey

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

Here's 2 cents. I am working on a similar problem with my 96 4.3, and my friend, who is a car mechanic, told me that the heads have issues with the valves sinking into the head because of valve seat problems. They may not be hardened seats. On mine, I have 3 cylinders, two on one side and one on the other, with low compression (40 to 80). He tells me that the bottom end of these engines is quite sturdy and he suspects the heads before the bottom end, with three low cylinders. You may want to get the heads checked at a machine shop.

Chris
 
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TilliamWe

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

The valve issues on my 97 5.7 Vortec were caused by me "lugging" the engine. The lugging caused high combustion chamber heat, which tulipped multiple valves.

Monte, was your engine reaching its proper WOT RPM prior to the loss of power?
 
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onebighead

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

thanks for the good responses. It seems that the boat was running fine until a time when I just started loosing power, a little backfire, then limped back in. TilliamWE, it was making good rpm. I didn't have it at wot except on take-off.
 
Bondo

Bondo

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

Monte Davis said:
thanks for the good responses. It seems that the boat was running fine until a time when I just started loosing power, a little backfire, then limped back in. TilliamWE, it was making good rpm. I didn't have it at wot except on take-off.
Click to expand...

Ayuh,.... So how much water was in the fuel filter,..??
 
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Maclin

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

Monte,

Regarding what may have been a contributing factor to the eventual failure, TilliamWe was asking if the engine can reach the top of the recommended WOT RPM range with the boat having a normal load. If not then it may be over-propped and the engine is lugging. That overheats valves and seats. That, along with other contributors (bad fuel, etc), will eventually shorten the life of the engine.
 
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TilliamWe

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

Maclin said:
Monte,

Regarding what may have been a contributing factor to the eventual failure, TilliamWe was asking if the engine can reach the top of the recommended WOT RPM range with the boat having a normal load. If not then it may be over-propped and the engine is lugging. That overheats valves and seats. That, along with other contributors (bad fuel, etc), will eventually shorten the life of the engine.
Click to expand...

Exactly, thanks for the followup.
 
O

onebighead

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Re: 4.3 mercruiser with burned exhaust valve.....what could cause this

thanks again for all the posts. I'm not sure what caused all this with my boat, but happy to say that today got it back together and it started and ran fine on the muffs, (no load). I will get it to the lake for a try as soon as I can. Also Bondo, only a little water in fuel filter can.
 
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