whats my next troubleshooting step?

[couger300]

if anyone has read past threads i had a piston basically overheat and melt in the cylinder. i'm waiting for the manual to arrive to start that whole tear down process. i'm really looking to narrow down what actually caused this. i started with removing and disassembling the carbs hoping to find some sort of blockage in the jets. found nothing. i was really surprised how spotless these things were. i did have a problem with water in the oil tank that i thought i took care of. i'm kind of thinking that may have caused that piston to over heat a time or two and it finally s...t the bed when i was able to get the engine up to speed. none of the other cylinders were harmed. from what i can see. new to this whole thing so im wondering what i should check next. any suggestions are very welcome! thanks guys, you have been great through this whole process. oh the engine is a 95 johnson 90hp. j9tleor

 

[Joe Reeves]

Re: whats my next troubleshooting step?

If the engine's piston actually melted down, it was caused by pre-ignition.

This is usually caused by:

1 - A slightly fouled carburetor which results in the related cylinder running lean. Did you actually remove the high speed jet and inspect it closely?

2 - A small piece of steel jammed in the combustion side of the cylinder head. This would glow like a model airplane glo-plug which would result in detonation at various times, all of which would be disasterous.

3 - A ever so slightly failed head gasket, flawed just enough to allow a very mild amount of water spray into the cylinder, not enough to cancel out ignition but enough to increase the compression ratio and the heat factor.... results in the same melted piston damage.

 

[nwcove]

Re: whats my next troubleshooting step?

just a thought, but ive seen pistons with holes burnt through them, in non outboard two strokes, caused by a bad crank seal, allowing the engine to suck air in and leaning out the cylinder, with the other cyl(s) remaining in pristine condition.

 

[couger300]

Re: whats my next troubleshooting step?

the gasket looked like crap to me. it was rusted and bubbled basically crumbled at the bottom of that cyinder. this is what i meant by melted. yes i did tke the high speed jets along with everythinr else i could get apart and everything looked to be on the up n up. i was thinking maybe the vro or whatever its called but i think i would have damaged more than one cylinder.

 

[Joe Reeves]

Re: whats my next troubleshooting step?

Sounds like the gasket was the culprit.

 

[couger300]

Re: whats my next troubleshooting step?

i should clarify it was the head gasket that was crap. were you talking water from the cooling system?

 

[Joe Reeves]

Re: whats my next troubleshooting step?

Yes, when a head gasket starts to fail ever so slightly, water will enter he combustion area.

However, that piston has not encountered a pre-ignition scenario. That scoring of the cylinder wall and piston skirt would indicate a lean running cylinder.

Running a engine with excessive water entering the cylinder would result in scoring of course BUT that cylinder wouldn't be firing.

Have you had this engine for a number of years and this problem slowly came into being OR is a engine that you just bought in this condition?

 

[couger300]

Re: whats my next troubleshooting step?

believe it or not the majority of that is melted aluminum. i have flaked some of it off. i if you look closely its actually raised. i dont know of that changes your thoughts but i thought id let you know.

 

[couger300]

Re: whats my next troubleshooting step?

just bought it. ran good on the first time out. but we only had it runnung for 15 minutes or so. just went to the beach and anchored. second time it would stall after giving it some throttle. drained bowls and there was water. pulled feul tank and lines no water. decided to pump out oil tank, half a gallon of water in there. next time i took it out this happened. it was going great at wot then it just shut down after 30 seconds. thought feul problem so i fired it back up after pumping the bulb. same thing again. this time it would not fire.

 

[couger300]

Re: whats my next troubleshooting step?

sorry about the typing! the wife was talking to me about how much time i spend on this site!

 

[nwcove]

Re: whats my next troubleshooting step?

which cyl was it? top, middle or bottom? sure seems carb or seal related. maybe even oil delivery?

 

[couger300]

Re: whats my next troubleshooting step?

i believe its #4. i dont have the manual yet. its the lower on the feul pump side. from what little i know i thought so also. i really dont know how to test the oil delivery system on this thing. any ideas on how i can test it without a running engine? when i got home that day i drained the bowls to check for water again, there was no water but i noticed that the feul wasnt discolored at all from being mixed. i belive it should be. the system was mixing the water in the oil tank with the gas which lead me to belive it was functional.

 

[couger300]

Re: whats my next troubleshooting step?

i think it would have done some sort of damage to at least one of the other 3 if it wasnt working.

 

[Joe Reeves]

Re: whats my next troubleshooting step?

I strongly suggest you either replace or rebuild the VRO..... they're not designed to pump water.

The cylinder looks to me that it was run without lubrication which caused a great amount of friction/heat which in turn tore the aluminum piston skirt to pieces and scored the sleeve bad.

If pre-ignition existed, that sharp top intake edge opposite the exhaust slope would have actually been melted down like an acetylene torch was applied to it. The aluminum you removed was from the piston skirt..... it would have been impossible to remove pre-ignition aluminum from the piston as it would be part of the piston itself.

 

[boobie]

Re: whats my next troubleshooting step?

I would have to say the water in your oil tank caused all of your problems.

 

[couger300]

Re: whats my next troubleshooting step?

more than likely it was the water. just wanted to eliminate everything else that i can before i get this back together and it happens again. thanks for the help!