Viper Piston Burn Down

ViperWarlock02

ViperWarlock02

New member
Joined
Dec 7, 2010
Messages
6
Age
56
Location
Michigan
Took the '02 Viper out for the first blast last week. After about 30mi, had a loud backfire and then only two cylinders. After limping home on two, we pulled the top end apart and found a completely destroyed piston #1. Took out the cylinder head and cylinder core as well. The piston looks like a melted candle with pieces of piston ring imbedded in it. Ugly carnage.

Look to complete the rebuild tonight (pending parts deliveries) but I am interested into the cause of this. I have read up on ethanol issues and fuel degradation caused from the ethanol/water. Would this have caused a burn down on only #1 cylinder? The other two cylinders look like new and the pistons have average to light carbon (3800mi). Carb boots and reeds are fine and I am running stock equipment. I have checked for kinked fuel and oil lines and all looks good.

Just want to know that I can blame this on bad fuel but I find it odd that 2/3rd of the engine looks like new.
 

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That sucks. Did you clean your carbs before the season started or did you you just top it off and go?
 
For only one piston to detonate and melt down like that is most likely due to a lean condition only effecting the particular cylinder.

Possible cause of leaness:
-PTO seal leaking air
-plugged/dirty jets + carbs
-plugged "top hat' filter under float needle + seat
-carb boot leaking or cracked
-water in fuel or iciing

An overheat condition could also cause this cylinder to detonate.

Old or low octane fuel

Ensure you have a real good look at the lower rod bearing on this cylinder...if in doubt its time to pull it right apart and get the crank checked and possibly rebuilt, that way you can change all the seals as well.

It would be a shame to put this back together without determining the cause to only have it happen again!

JM.02c

Bob
 
What he said - just want to echo - be sure to find the root cause, otherwise it will only happen again
 
I did clean out the carbs before the season began. I thought that maybe in the process of cleaning I could have dislodged something but i find it hard to believe to that much damage in 30mi. It wasn't a hard 30mi either.

The tank was about 1/2 full before the season started (and probably mid-octane) so at least half of it had been sitting all summer. With summer heat and cooling, that is why I thought of the ethanol and gas separation issue. But really, could one piston have melted that fast after 30mi?

The carb boots are fine - was the first thing we looked at before pulling the top end.

If it was a fuel issue, wouldn't that have failed all of the other cylinders? The others ones are almost perfect.

Thanks for the input, I'll re-clean all three carbs before final assembly.
 
change all gas out for new. also check for air leaks. carb boots. that burn down looks like an air leak is the problem. clean the carb boots and get new gaskets. retorqe the bolts.
 
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You should have not driven it after the melt-down. You lost any clues to the root cause by letting the piston beat itself to death. The piston will tell you why it burned down, but not after 30 miles of grenading.
 
I hate to be rude be it looks like you don't take very good care of that sled dude. If you treat it right it will return the favor.
 
Were there any other drivability issues prior to the backfire? Did it idle and run OK? Carb issues usually offer some hints before a total meltdown, though much of the damage in the pics likely occurred during the limping home.

Scary !!! As an owner of an '02 Viper, this stuff really scares me ! I always clean my carbs, but before the first trip I will also definitely drain the tank this year and blow out the fuel lines to make sure I have all the ethenol devils out.

Our cabin is remote, so we have always filled up at the end of a weekend to make sure we were starting full when we came back. With ethenol, I beginning to believe the better idea is siphoning the tank totally empty and bring a 5 gal can of fresh fuel up to start each trip.
 
Engine was running fine just before the backfire. It was for that reason that we thought it was the carb boot that caused the backfire in the first place and lead to the lack of power.

Reassembly is planned for tonight but that will depend on the crankcase seal (thanks sideshowBob). We will give the carb boots a thorough go over before starting it again and I have already drained all of the fuel out of all of our sleds. I'll also be replacing ALL of the gaskets so I hope to correct this air leak issue.

Could this have been something with the power valve assembly? Air leak on one of those gaskets. Just throwing it out there.

Anyboby hear (an/or use) of StarTron? This is a fuel enzyme additive that is supposed to help 'control' ethanol and fuel degradation. Good for 2- and 4-stroke engines and the diesel industry has been using it for years.
 
A leak around the exhaust valves would not have caused this. Normally the cause of a lean condition would be on the intake side of the engine...something that is creating a situation where you have too much air and not enough fuel.

Another thing to check would be that your thermostat is functioning properly to ensure the engine was not running too hot.

Bob
 
Burn Down avoided

So I parked my SRX last March after a successful season of riding. Pulled it out 2 days ago, for the first ride of the season and rode it to the gas station, which is approximately 6 miles away, plenty enough time for warm-up to see how she was running. On the way I noticed it ran great up top, but down low wouldnt run 'quite right'. Idle wasnt right either, idled a little too low. I pulled out the plugs at the gas station, 2 were nice and chocolate, and the PTO plug was dark, almost wet. I thought sweet, fouled plug, grabbed a brand new spare and threw it in, rode back to the cabin from the gas station. Still ran great up top, not quite right down low, and noticed the transition 'onto the pipe' was way more violent than its supposed to be. Got back to the cabin pulled out the new PTO plug and it was way white. So I said to myself the pilot on the PTO cylinder must be plugged. I pulled the airbox, plugged the coolant line, rocked over the carb rack and pulled off the bowl on the PTO carb, which was spotless, no varnish in it (in which there shouldnt have been, rode it all last year and the leftover fuel wouldnt varnish between spring and winter seasons), removed the pilot, and I couldnt blow air through it, or see light through it. Pushed a piece broom bristle through it backwards (it was all I had)and knocked out the piece of $4!# that was plugging it. Blew carb cleaner through it in both directions, checked the main , which was perfectly clear. Re assembled, and away I went. Rode scarefully all weekend, last long time.

After literally holding a 97 SX700 wide open across Michigan's U.P. for approximately 6000 miles without a single failure of any kind, I would be willing to bet that 95% of Yamaha carburated engine failures are a direct result of something as simple as a plugged jet.

It is important to remember that carburetors equipped on Yamaha snowmobiles (and most others) work as follows: Total fuel delivery = Pilot circuit+Main circuit. If one of the two circuits is plugged, that cylinder is now lean. This will eventually result in premature failure of the engine. In addition, the colder the outside temperature, the sooner failure will occur, and the higher the load on the engine, the sooner the failure will occur. plugged jet + cold temps + running the @#$% out of it = eminent failure.

In an earlier post, it was mentioned that the carbs were cleaned. A thorough job of cleaning the carbs comprises more then just pulling off the bowls, and making sure they are spotless. To what extent were the 'carbs cleaned'? At a minimum, you must remove the pilot and the main, and make sure liquid will flow through both. It also helps to blow carb cleaner through ALL passages in the each carb. This insures all fuel and air circuits are free of debris.

Keep in mind, during all of this, my father is itching to try out his new FX Nytro. We wanted to ride, but taking the time to check something 'not quite right' saved my engine. No matter how bad you want to ride at that moment, do not be in denial about having to fix something. Git R Done. It could save you a LOT of $ in the long run. :2strokes:
 
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J4nij is exactly right. It doesn’t take much to plug a jet. Two years ago my 03 Viper did the exact same thing in the same cylinder. When I took my carb apart I found a soft jell like speck in the main jet, the rest of the carb was super clean. Now I always empty my tank and run the gas out of the carbs for the summer and I always clean my carbs before the first ride of the winter. Your problem was most likely a plugged jet or bad gas. You should never drive it after you burn it down unless it’s a life threatening situation. It’s probably what ruined your head and cylinder. You will also, most certainly have aluminum chunks in your crankcase. It’s not easy to do but you will need to flush out your crankcase before you put it back together. Cracking your case is a little extreme but it is the safest way to go.
 
p4nij said:
So I parked my SRX last March after a successful season of riding. Pulled it out 2 days ago, for the first ride of the season and rode it to the gas station, which is approximately 6 miles away, plenty enough time for warm-up to see how she was running. On the way I noticed it ran great up top, but down low wouldnt run 'quite right'. Idle wasnt right either, idled a little too low. I pulled out the plugs at the gas station, 2 were nice and chocolate, and the PTO plug was dark, almost wet. I thought sweet, fouled plug, grabbed a brand new spare and threw it in, rode back to the cabin from the gas station. Still ran great up top, not quite right down low, and noticed the transition 'onto the pipe' was way more violent than its supposed to be. Got back to the cabin pulled out the new PTO plug and it was way white. So I said to myself the pilot on the PTO cylinder must be plugged. I pulled the airbox, plugged the coolant line, rocked over the carb rack and pulled off the bowl on the PTO carb, which was spotless, no varnish in it (in which there shouldnt have been, rode it all last year and the leftover fuel wouldnt varnish between spring and winter seasons), removed the pilot, and I couldnt blow air through it, or see light through it. Pushed a piece broom bristle through it backwards (it was all I had)and knocked out the piece of $4!# that was plugging it. Blew carb cleaner through it in both directions, checked the main , which was perfectly clear. Re assembled, and away I went. Rode scarefully all weekend, last long time.

After literally holding a 97 SX700 wide open across Michigan's U.P. for approximately 6000 miles without a single failure of any kind, I would be willing to bet that 95% of Yamaha carburated engine failures are a direct result of something as simple as a plugged jet.

It is important to remember that carburetors equipped on Yamaha snowmobiles (and most others) work as follows: Total fuel delivery = Pilot circuit+Main circuit. If one of the two circuits is plugged, that cylinder is now lean. This will eventually result in premature failure of the engine. In addition, the colder the outside temperature, the sooner failure will occur, and the higher the load on the engine, the sooner the failure will occur. plugged jet + cold temps + running the @#$% out of it = eminent failure.

In an earlier post, it was mentioned that the carbs were cleaned. A thorough job of cleaning the carbs comprises more then just pulling off the bowls, and making sure they are spotless. To what extent were the 'carbs cleaned'? At a minimum, you must remove the pilot and the main, and make sure liquid will flow through both. It also helps to blow carb cleaner through ALL passages in the each carb. This insures all fuel and air circuits are free of debris.

Keep in mind, during all of this, my father is itching to try out his new FX Nytro. We wanted to ride, but taking the time to check something 'not quite right' saved my engine. No matter how bad you want to ride at that moment, do not be in denial about having to fix something. Git R Done. It could save you a LOT of $ in the long run. :2strokes:
Click to expand...


DEAD NUTZ ON POST!!! AWESOME!!!!
 
Good news - we completely tore down the carbs last night and I did find that the #1 carb was a little gummed up in the main jet. Everything is now thoroughly cleaned and I can rest at night (and at WOT) that the cuase of the problem has been located.

Bad news - the piston pin needle bearings I ordered from Shadetree Powersports were the wrong ones. They do not fit in the piston "shell" due to the length. The ID and OD is correct but they are too long. Shadetree lists three different bearings...24mm, 22.8mm and 21.8mm. I talked to them and are waiting for a call back on the correct size but I wanted to post this question. Does anyone know what the correct needle bearing length is for stock 69mm bore pistons? Yamaha part #93310-32009-00 (needle bearings).
 
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