What would be the next step

[Thumbtack]

Merc v-8 thunderbolt 4 fresh water. not sure year or model number. Had one cylinder (7) about 20psi compression, determined it had an exhaust valve that is either not closing all the way or tuliped. Don't remember the boat ever overheating. What would the next step be? Is the only next thing to do is remove the head to examine further?

 

[Bondo]

Re: What would be the next step

What would the next step be? Is the only next thing to do is remove the head to examine further?

Ayuh,.....

Pull the Heads,+ head for your local Machine Shop,....
Might want to stop by a Parts House,+ Grab an Upper Motor Gasket Set too.....
Your Machinest will tell you where he gets his,.....

 

[Speakrdude]

Re: What would be the next step

Verify the timing. Make sure its not detonating. Quality of gas? Check all the fuel filters, fuel pump pressure, Anti-siphon valve, anything that could cause a lean condition.
Had the same problem 3 times in a row. After pulling the heads and replacing a bad valve the 3rd time, I was determined to find the problem. So-far-so good.

Good luck.

Jim

 

[TilliamWe]

Re: What would be the next step

Is the bottom of the boat clean? What WOT RPMs are you able to turn? Engine coolant overheat is not what causes the problem. Combustion chamber temps being too high causes it. And "lugging" the engine causes that. Dirty/fouled hull or a prop that is "too big" and doesn't allow the WOT RPMs to get into the manufacturers range causes higher combustion chamber temps. Been there, done that. If you have Vortec heads (1996 or later) don't be surprised if it's actually cracked too.

 

[Thumbtack]

Re: What would be the next step

Thanks guys, i will bring the heads in to the shop to see what is wrong with the valve and go from there. Thanks for the quick replies

 

[Windykid]

Re: What would be the next step

Ever think of adjusting the valves on that cylinder for s$!ts and gigles?