1982 90hp Johnson V4, Melted piston

[alanR1]

Ok, it is my turn to spill the info on my burnt up piston on my motor. Here is the history. Bought a boat and motor with seized motor. Broke it loose. Rebuilt carbs, thermostats, water pump, fuel lines & vents & pump. Ran great on the hose, put in water and took some work to get it to idle right in water. Did decarb, ran this weekend for the first time and ran like a scalded dog for about 30 minutes. Slowed to a stopp and it quit. Restarted and ran for about 2 minutes and slowed down and it stopped and made a grinding noise. Towed it in and brought home. NOW to get down to it after the history and everything, I pulled the plugs and the top starboard side cylinder has aluminu on it, pulled the head and cylinder is pitted and there is a little piston melted to the head. <br /><br />oem plugs(champions)<br />87 octane fresh gas<br />tcw3 oil<br /><br />Any ideas on what I should do, I want to try and check for compression and if its there I want to try and polish out the piston and head(not much pitting at all) and try and get it running again. But that brings me to what caused the meltdown and will it happen again. Any suggestions. Thanks

 

[DJ]

Re: 1982 90hp Johnson V4, Melted piston

alanR1,<br /><br />Don't kid yourself. The engine has to come apart and a COMPLETE rebuild performed.<br /><br />My guess it was seized due to a stuck ring. Some damage had already been done. It was just a matter of time.

 

[alanR1]

Re: 1982 90hp Johnson V4, Melted piston

The previous owner overheated it and blew the head gaskets one after another. Changed the gaskets, flushed it and let it sit for 2years while working on the floor of the boat. Left hood off of the motor for who knows how long. I cleaned and replaced everything and had it running beautifully on the whose for well over an hour. Previous overheat was due to stuck thermos, clogged water passages all the way around from saltwater, and a bad water pump. I fixed al of that. Can I remove the one piston and replace it only. There is no scoring in the cylinder really, just a hardly noticeable abrasion. This is a old motor and I dont want to spend hundreds on it.

 

[DJ]

Re: 1982 90hp Johnson V4, Melted piston

alan,<br /><br />You can fix one cylinder. That is no problem. However, do we really know where all of that material went?<br /><br />Do we know that we didn't have a carb lean out?<br /><br />Also, the V-4's have cooling water deflectors in the heads. Are those OK?<br /><br />I understand what you trying to accomplish, just know that it will be a patch.

 

[alanR1]

Re: 1982 90hp Johnson V4, Melted piston

Answers: I am pretty confident that everything stayed in the top of the cylinder, it shut right down and i didnt try and start it back up, and the cylinder heads are in good shape, it has very little imperfection on it. It can be polished with very little effort. I just rebuilt the carbs and I did a decarb days before running on the water. I am wondering how it could have happened, all of the other cylinder are burninf perfect. Can I remove the piston by take the circlips off from the inside, behind the intake manifold. I can get pretty good access to the back of the piston. I know that all of the jets are clean. Whats next?? I will try and get you a picture of the cylinder and piston in a few.

 

[alanR1]

Re: 1982 90hp Johnson V4, Melted piston

^

 

[NathanY]

Re: 1982 90hp Johnson V4, Melted piston

I dont understand, DJ is one of our most respected and revered members. What do you want him to say?<br /><br />I agree with him 100% on this one. <br /><br />If you replace just the piston and rings with out boring or honing the cylinder, you WILL be in the same boat you are in now very soon, and I doubt that you will get any compression on that cylinder at all, doing it your way.