Lets play a game called 'What happened to my piston'!!

[Biggieb400]

Engine Model TE60TLCEA

Engine had an overheat issue at the beginning of the summer, following an impeller replacement. Hit the overheat alarm a couple times during troubleshooting on the water. We never ran it with the alarm disconnected. I was finally able to trace the issue to a faulty thermostat, which I replaced. She ran great for a few weeks. Buddy had the pontoon out on the water and noticed a sudden loss of power, said it felt like it was running on 50% power. He limped it to his anchor point, fired it up and limped it back to the trailer. A week later we took it out to see if the issue persisted, engine only ran up to ~50% of max RPM. In hindsight we should have pulled the spark plugs following the first signs, but I'm not sure it would have made a difference given the amount of debris that we found in the #2 plug gap.

I recently disassembled the engine to find cylinder scoring and a broken piston skirt in the #2 cylinder. The other 2 sleeves has some light scoring, but no metal or aluminum shavings. I want to ensure I fully determine cause prior to running the rebuilt engine. I haven't been able to find any debris in the #2 carb that would prevent fuel flow, engine is still running VRO system with some pre-mixed fuel for insurance.

Looking for ideas. Thanks in advance.

 

[AviatorJim]

Re: Lets play a game called 'What happened to my piston'!!

Ah, very nice. Well, the overheat melted the piston a bit, and removed the heat treatment. Add to that a little deformation and the friction (a 2 stroke cooled and lubricated by the fuel/air mix, which is also burned for combustion doesn't have the cool oil being sprayed on the undeside of the piston and cylinder walls), and you have a perfect situation for destroying a piston, and scuffing the heck out of the cylinder walls.

But if you fixed the cooling issue, and don't have a contributing problem of a very lean carb you might be fine. If you can find a shop to fix those bores. And you likely also ruined the head, and case around that cylinder due to overheating. No real fix for the metal getting soft. But if you don't run it hard it might last a while. I'd look for a new powerhead.

--Jim

 

[daselbee]

Re: Lets play a game called 'What happened to my piston'!!

Well done man!!! That is some spectacular burndown. I burned one down once, but it was nowhere near as good as yours.
But seriously, I hope you find what caused that....

 

[Biggieb400]

Re: Lets play a game called 'What happened to my piston'!!

Thanks for the input so far. I'm not buying overheat as the root cause nor lack of fuel/oil. The main bearings look good, the scorched cylinder wrist pin shows no signs of excessive heat either nor is it seized.

Did a ring break leaving debris that destroyed the piston skirt? Did that debris then ground out the spark plug causing detonation that left the craters with the rounded over (melted) edges??

Was there an ignition issue?? If so, is it common to only have 1 cylinder fail? Coil??

Was it a fuel quality or octane issue? Typically center cylinders run a larger main jet. Is that common in marine engine?? I haven't compare the three carb main jets yet.

Keep the ideas coming...

 

[Lyle29464]

Re: Lets play a game called 'What happened to my piston'!!

It got too hot. Post number 2. Piston got too big. too tight. too dry.

 

[BigNateK]

Re: Lets play a game called 'What happened to my piston'!!

I have a simlar looking mess on my bench! i think mine was due to a lean condition. i also noticed on mine that a few of the reed pedals werent closed all the way but im not really sure if that would cause a lean mixture or just poor preformance

 

[noelm]

Re: Lets play a game called 'What happened to my piston'!!

lean burn, no doubt about it, fix your carb problem NOW!

 

[Biggieb400]

Re: Lets play a game called 'What happened to my piston'!!

lean burn, no doubt about it, fix your carb problem NOW!

Thanks for the input. I need to get out the carb cleaner and blow nozzle and start checking the passages and orifices of the carb. I was expecting to find a big chunk of rubber fuel line or something similar in the carb bowl but nothing so far. I'll try a piece of small wire through the standpipe for the high speed circuit of the carb and see if that dislodges anything. I also need to make sure it isn't the fuel line as well.

Folks need to understand overheating doesn't melt the top side of the piston, or the cylinder head. It might warp the head and cause a leak, but it's not going to melt it. If the damage was the sole result of overheating, I'd have piston scuffing/scoring without the piston face and cylinder head damage...

 

[Biggieb400]

Re: Lets play a game called 'What happened to my piston'!!

I have a simlar looking mess on my bench! i think mine was due to a lean condition. i also noticed on mine that a few of the reed pedals werent closed all the way but im not really sure if that would cause a lean mixture or just poor preformance

You'd probably suffer from low compression and possibly some minor back flow through the carb (which probably isn't good for it). What is hanging the reed valve open? I had a lot of ground aluminum in the center cylinder cavity, but I don't think it was interfering with reed valve operation. I have a lot of cleaning to do on the reed valve to remove the debris before reassembly.

Best of luck with your rebuild...

 

[Silvertip]

Re: Lets play a game called 'What happened to my piston'!!

The pitting on the piston crown is a sure sign of detonation which may be due to timing, lean carburetion or both but more than likely a lean carb issue. Once the upper ring land is gone the scoring begins and things fail quickly. Someone suggested debris closed up the plug gap which caused detonation. With no spark detonation is not possible. If you repair this engine, make sure you clean and rebuild all of the carbs -- not just the one on that cylinder or you may be doing the job again. Reeds that are not sealing may affect idle quality as they are intended to reduce spit-back through the carb. They would not have a significant effect on high speed operation unless a piece of one passed through the engine..

 

[TN-25]

Re: Lets play a game called 'What happened to my piston'!!

Twin carbs on that engine, right? If only one is working as it should, the other could starve and lean out the cylinder that it feeds, leading to devastation due to lack of lube and high temps because of a lean condition, leading to...

That is some impressive destruction.

Carb sync! Multiple carbs should be sync'd.

 

[mercuk]

Re: Lets play a game called 'What happened to my piston'!!

WOW!!! Thats a great effort... Nice one... I'm not qualified enough to give you an answer to what exactly went wrong but either way, the pics are rather impressive!!!!
In all seriousness good luck to what ever you decide to do... I would probably try and find a decend replacement powerhead though, that one looks beyond knackered!:lol:

 

[aerobat]

Re: Lets play a game called 'What happened to my piston'!!

hope your wife is not frustrated that you now has a saggy piston :facepalm:

thats a massive damage i must say , but i think your engine is nice for diy work and parts are relativly cheap. good luck !

 

[Biggieb400]

Re: Lets play a game called 'What happened to my piston'!!

Twin carbs on that engine, right? If only one is working as it should, the other could starve and lean out the cylinder that it feeds, leading to devastation due to lack of lube and high temps because of a lean condition, leading to...

That is some impressive destruction.

Carb sync! Multiple carbs should be sync'd.

This engine is a 3 cylinder model with 3 individual carbs... I've only inspected the center carb, but do plan to go through all 3 before I start it for the first time.

 

[jbjennings]

Re: Lets play a game called 'What happened to my piston'!!

I personally think it's a super lean center carb in combo with a possible overheat. I like to take the cowl off and have a helper run the motor and look at the carb throats when running on plane. You should see fuel coming out the high speed nozzle, and all 3 carbs should look like they have the same amount of fuel coming out. You may also consider checking for vacuum leaks associated with that cylinder which would also cause it to lean out. I'd consider a used powerhead with good compression since that cylinder is likely going to need resleeving/new piston/etc., and you need a new cylinder head anyway at the very least. Since you mention that the other cyl./pistons have scoring as well and it will take a full rebore with new pistons, I'd for SURE go with a used powerhead if the motor is more than 20 years old. BTW, did you notice a kink in the oil line going to that carb? Could it be a total lack of oil due to a pinched or blocked oil line?
ANyway, you seem to be familiar with 2-stroke outboards already, and I'm no professional outboard tech so my input is probably useless. I hope you figure it out and post back, as I'm curious.

 

[ondarvr]

Re: Lets play a game called 'What happened to my piston'!!

Folks need to understand overheating doesn't melt the top side of the piston, or the cylinder head. It might warp the head and cause a leak, but it's not going to melt it. If the damage was the sole result of overheating, I'd have piston scuffing/scoring without the piston face and cylinder head damage...

You can easily melt the top of the piston when its running lean, but the damage on the piston top and head on your motor is from bits of the ring and piston being smashed between them, that's why the damage is only around the edge where there is very little clearance at top dead center.

 

[Biggieb400]

Re: Lets play a game called 'What happened to my piston'!!

You can easily melt the top of the piston when its running lean, but the damage on the piston top and head on your motor is from bits of the ring and piston being smashed between them, that's why the damage is only around the edge where there is very little clearance at top dead center.

I agree with your statement, that's why I'm having a tough time deciphering whether this failure was a result of a broken ring, piston skirt or detonation. The pieces of the piston skirt and top ring that got between the piston and cylinder head lead to significant damage, but the fact that the gouges on the head and piston head are 'melted' and rounded over suggest combustion was occurring after the interference damage occurred. The melting that occurred was likely due to sharp edges and normal combustion temps. I'd be inclined to think the piston skirt broke due to the excessive side loading caused from the debris present between the piston and head surface, or excessive loading when the piston got caught on one of the intake or exhaust ports...

I've heard that the small pins used in the piston ring grooves to prevent ring rotation can work themselves loose over time. If the pin works its way out, the ring is free to rotate and the end could get caught in an intake or exhaust port. You can also have that pin floating around in the engine. You can see damage in picture 2, where there is a significant portion of the piston missing between the piston face and top ring groove. Did the ring get caught here? You'll notice there is no top ring left either...

 

[bonz_d]

Re: Lets play a game called 'What happened to my piston'!!

I have to ask, at this point does it really matter what the root cause was? This is FUBAR'd and may never be able to determine the root cause. If it were a ring how will you tell? It's gone!

 

[V153]

Re: Lets play a game called 'What happened to my piston'!!

I have to ask, at this point does it really matter what the root cause was?

Evidently it matters to Biggieb?

 

[boobie]

Re: Lets play a game called 'What happened to my piston'!!

Agree +1....Find the cause so it doesn't happen again.