3.7 mercuiser burned piston

[bdreaper1234]

i just had both these engines rebuilt 200 hours ago and had new carbs installed 25 hours ago. 10 hours ago the #4 cyclinder burnt a valve after it blew a head gasket. So we fixed the head and installed a new gasket. Now 10 hours later it has burnt a piston on the same cyclinder on the same engine. I am positive that it is in time so i doubt that it is detonation. It looks a little like it blew the head gasket again. I have heard that it could be the head bolts may have stretched causing them to not torque down properly? Anyone heard of this? It also runs about 15 psi below the other engine on oil psi. It is still in limits on the oil psi but that seems odd to me. Any ideas?

 

[tommays]

Re: 3.7 mercuiser burned piston

I am positive that it is in time so i doubt that it is detonation<br /><br />the only thing that can burn a hole through a piston is detonation caused by ????<br /><br />i have only burnt pistons on motors i was raceing and have seen people do it in about 3 seconds its really easy if your pushing a motor hard<br /><br />the timeing may be correct but if the motor guy was sloppy all it takes is a small hot spot from something in the motor to do it<br /><br />these are really tame motors that should not be burning valves ,blowing head gaskets or haveing problems at all unless someone is really doing something very worng<br /><br />tommays

 

[bdreaper123]

Re: 3.7 mercuiser burned piston

These engines don't get run hard at all.

 

[DHPMARINE]

Re: 3.7 mercuiser burned piston

bdreaper123<br /><br />I just reread your post,and think you are running twin engines.Am I correct?<br /> If so check the gear ratio in the drive with the piston problem.<br />DHP<br />then please feel free to give me a call back.

 

[bdreaper123]

Re: 3.7 mercuiser burned piston

Yes you are correct i am running twin engines. My gear ratio is the same on both engines. I know this cause i had to replace both outdrives just after the engines. This boat has been a fun one! NOT!

 

[bdreaper1234]

Re: 3.7 mercuiser burned piston

could it be that the cyclinder was runnin lean for some reason? The other cyclinders didn't look lean. If a carb is running lean can it only effect one cyclinder? It ran great until it burnt the piston.

 

[DHPMARINE]

Re: 3.7 mercuiser burned piston

My idea is if the wrong ratio is on the problem engine,it is working too hard.Just because they were replaced does not insure the correct parts were used.Might be worth checking.Had this happen to a 4.3L with a 1.50R instead of 1.64.We found this after 3 #1 pistons.Also what you ask about the head bolts is correct,they can fail.some shops replace every time,we replace if there is a second failure.<br />DHP<br />Oops,forgot this was a 3.7L.They also had a problem with coolant resevoir/manifold gasket,causing wrist pin problems on #4 piston.

 

[DJ]

Re: 3.7 mercuiser burned piston

I'm thinking like DHPMARINE. Overworking the engine-wrong ratio.<br /><br />Also, look for vacuum leaks at the intake and carb base gaskets.

 

[imported_Mike_M2]

Re: 3.7 mercuiser burned piston

I would look into the carb as the problem. Wrong jets in a carb can cause a motor to run rich. If that happens you can absolutely burn a valve or piston, i know because i've done it! Years ago, playing around with a backyard racecar i had i installed the wrong jets in my holley 850. I noticed the headers glowed extra red but didn't put 2 and 2 together until it was too late. A few runs on the quarter mile and it was ready to rebiuld, finding a couple burt valves and a small hole in one piston. Of course, it's impossible to see your exhaust heating up in a boat. Come on, 190 hours and no problem until you changed the carb? Too much coincidence if you ask me. Put the old carb back on and i bet your problem goes away.

 

[bdreaper123]

Re: 3.7 mercuiser burned piston

Thanks for all the ideas. I'll post how it goes.