Cause of Piston failure

[schematic]

Hi all
I've been given a repair on a 1993 VE115TLETS Evinrude 115hp (1993). Before I proceed, I would like your opinion on the piston failure which occured on the bottom cylinder "starboard" bank. The upper cylinder piston is just starting to gawl, but as shown in the photo, the bottom piston is badly melted. I also found an exhaust leak at the engine base gasket which is shown as well. Since I don't have a history on this engine, what cause is most likely?

Thanks in advance...

 

[Mas]

Re: Cause of Piston failure

No oil or cooling water. I do not know which, but both will cause an overheat. Sorry, not much insight.

MAS

 

[Mas]

Re: Cause of Piston failure

Also, were the proper spark plugs used?

MAS

 

[emdsapmgr]

Re: Cause of Piston failure

If the upper is starting to scuff like the bottom, it is possible that that side of the engine is running hot. Did you get a warning horn? Check the thermostat housing for working stats and that the pressure relief valves are able to function on that side of the block. Also, too much high speed timing advance can cause this. A side issue would be an autopsy on the side of the carburetor which feeds this piston. Especially what each of the jets looked like. Possible the high speed jet on that side has some debris in it, blocking fuel/oil flow. Base gasket failures on this engine are common. They usually involve exhaust gas leakage and not cooling water leakage. Not unusual for them to continue to run with this problem for some time. Though messy, it is unlikely the exhaust leak has anything to do with this failure. Good time to remedy this is when you pull the powerhead for repairs.

 

[schematic]

Re: Cause of Piston failure

Update for anyone interested:

-Found the VRO oil line pinched under starter motor. (owner said he had beeps but ignored them)
-Found the fuel line coupler at the engine had been replaced with a jobber one and wasn't held in far enough by the thumb release. The fitting sucked air badly.

Once the engine started to miss badly, the owner took it to a marine shop who told him he had no compression in #3 cylinder likely caused by a bad VRO.

Its funny how often the VRO gets a bad rap, but really seldom fails...

 

[jonesg]

Re: Cause of Piston failure

or when the vro is beeping its heart out trying to warn the owner...

and gets ignored.

 

[schematic]

Re: Cause of Piston failure

or when the vro is beeping its heart out trying to warn the owner...

and gets ignored.

Actually the owner told me he had someone local look at it for the beeping problem early in its life and was told it was a defective oil level sensor in the oil tank. He was told to keep the tank full and ignore the beeping.
Costly advice eh?

 

[emdsapmgr]

Re: Cause of Piston failure

From your description of what you found, it seems odd that the problem only occurred on the one side of the engine.

 

[schematic]

Re: Cause of Piston failure

emdsapmgr
The other pistons showed some scuffing. I assumed that the main jet in #3 may of had debris blocking it, but didn't find any. I also found the "recirculating check valve" on the failed side wasn't holding in one direction. The relief valve in the thermostat housing for the failed side had some algae jamming it up. Put all of this together and the poor engine was doomed. I'm not dead sure of the cause of failure, but the badly pinched oil line and sucking air problem were extreme. "chicken or the egg?"