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Melted Piston?

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ShoMeStyle

New member
Bought this Evinrude 115 crossflow(Not sure on year) from a marine shop about 2 years ago, everything has been great until this weekend. Was on plane cruising like normal and it lost power than died and over heat alarm went off. After I let it cool down, it struggled to start back up. When it did, I pulled wires on each cylinder, one at a time and found the cylinder that caused no change.

Got back home and pulled the spark plug. It is crusty and black.

Decided to take the cylinder head off to check the cylinder and it looks like the exhaust side of the piston melted off? Also on the top of the piston. I can touch the top ring and wiggle it but it doesn't appear broken.

Cylinder seems scored up and I believe has some melted metal stuck to it?

I obviously need to fix what caused this, but I'm not too sure what else to check...the carbs all seem good, nice and clean. The thermostats and water passages seem okay, stats opened up in boiling water.

I am new to working on 2 strokes and outboards. Although I'm mechanically inclined, I'm wondering if this thing is even worth salvaging and what my options are?

Do these motors have cylinder sleeves you can replace? or do I need to get it bored out? Will a hone suffice?

How hard is it to replace the piston?

I don't have the money for a new motor.

Thanks
 
You need 4 new pistons.----Likely needs 4 cylinders bored and O/S pistons fitted.----If you go ahead with this I suggest lower unit inspection and seal kit installed.
 
racerone said:
You need 4 new pistons.----Likely needs 4 cylinders bored and O/S pistons fitted.----If you go ahead with this I suggest lower unit inspection and seal kit installed.
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All the other cylinders look perfect. Can still see cross hatching from last hone in all of them. But the bad one has some vertical streaks in the cross hatching and I was able to get the melted aluminum or whatever it was off. Nothing that I can catch with my fingernail in the cylinder anymore. Wonder if I can get away with a hone in that one with a new piston and rings.

Does anyone happen to know the stock diameter of the 115 crossflow cylinder? I'm not sure if it has been bored out already by a previous owner.
 
racerone said:
It be 3.500"----Oversize pistons are usually marked.
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I see that now, thanks. The pistons that are in it have .020 marked on the top. Which means I could get it bored another .020 over and get .040 pistons and rings? But then I would have to look into re jetting the carbs probably huh?
 
Sounds like you have the project under control.----Did lots of these jobs myself.----You have to determine what caused it.----Or you will be doing it again !
 
racerone said:
Sounds like you have the project under control.----Did lots of these jobs myself.----You have to determine what caused it.----Or you will be doing it again !
Click to expand...

Yeah, I don't think it had water getting into the cylinder, like I said, it's been running great for almost 2 years. I don't think it was not enough fuel, although, maybe in hindsight maybe too much fuel washed out the cylinder? I pre mix 50 to 1 to bypass the injection. Can you still get washout with premix that would cause the piston to melt? Sometimes when I would tilt the motor up a little fuel would come out of the bottom of the air box.

As far as I know the spark looked good, although I don't know how to check for double ignition or timing.
 
Too much fuel washing out he cylinder?? Interesting theory. Seems like extra fuel would have extra oil too, wouldn't it? JMHO.
 
fdrgator said:
Too much fuel washing out he cylinder?? Interesting theory. Seems like extra fuel would have extra oil too, wouldn't it? JMHO.
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I did some research before posting and read that can happen but the poster didn't state whether that was for people still using the injection system or pre mixed. It's logical that with pre mix, over fueling shouldn't wash it out since it's still getting oil.

I believe it was getting enough fuel, the carbs are spotless and it was running great before hand.

I'm not sure how I could tell now if water was getting in the cylinder or not. The head gasket "looked" okay? And if water had been getting in, would it have ran good for two years? The damage looks like something that has been going on for awhile. I will try and post pictures. Using my phone makes it difficult to post them.

Like the said the damage was to the top of the piston and mostly the exhaust side was worn or melted away down to the first ring groove. I can take a small screw driver and actually pull the ring out while it's in the cylinder lol
 
The pistons are a given-they need replacement. What caused it?? You said it yourself, sudden cooling failure and overheat. A guess would be a spun impeller hub.
 
ShoMeStyle said:
I'm not sure how I could tell now if water was getting in the cylinder or not. The head gasket "looked" okay?

Like the said the damage was to the top of the piston and mostly the exhaust side was worn or melted away down to the first ring groove. I can take a small screw driver and actually pull the ring out while it's in the cylinder lol
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A cylinder with water intrusion will appear clean. A cylinder that is running rich will look black and wet in the middle.

On 2-strokes you should also have what's called piston wash. At the intake ports the fuel air mixture will 'wash' the carbon off the piston dome. An engine that is set up right should have a piston dome that is mostly all black except for clean areas about the size of your thumb nail at the intake ports. If the entire piston looks like clean aluminum you have water intrusion steam cleaning the dome. If you have a little black and a whole bunch of clean aluminum you likely have way too much fuel. Pre-mixing fuel vs VRO has nothing to do with any of these patterns.

The fact that your piston is all black and is melted at the exhaust port is a classic sign of a lean cylinder. The unburnt fuel cools the piston and when it is lean the cylinder temp is too high and the aluminum will melt.....most often at the exhaust port. The source of your lean condition could be something other than the carbs. You could have a bad intake gasket or even the seal on the case halves could be bad allowing air to leak into the block at that cylinder only. The fact that your pistons show aftermarket signs could mean the previous rebuilder didn't seal the block properly and that is the point of air intrusion that leaned out that cylinder.
 
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