[DevoMR]

I took my sled for a quick trip around the lake this weekend, and it died after about only 1/4 mile.

I was riding in about 8 inches of fresh snow, not going wide open (maybe 65 mph). I pulled the plugs and it looks like there is a hole in the top of one piston. The hole does not go all the way through, but its is definitely toast.

The sled was warmed up - my son had been riding it around for about an hour, never going more than 30 mph.

This is the second time this has happened to this sled. The first time I figured it was my fault since I was riding WFO in deep snow for several miles. But that was a couple of years and probably 700 miles ago.

If anyone has any ideas on what might be causing this, please let me know. I'm no mechanic by any means but I don't mind getting my hands dirty if I know what to look for.

 

[jak_nelson]

what type of plugs do you have and what does the plug look like for that cyl.

 

[ckoz71]

Well a couple of things come to mind, 1 are the right plugs in and are they gapped correctly(to much too hot etc)? what side melted down the first time and this time? is the oil pump working to both sides? check tubing, and are the carbs running equally(is one leaner than the other?) have to take them apart to be sure. good luck, any more questions dont hesitate to ask.
ckoz

 

[DevoMR]

what type of plugs do you have and what does the plug look like for that cyl.

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I use BR9es plugs, which is what the owners manual says to use. The brand is NGK) The plug for the burned up cylinder is gray/white and looks like the electrode is partially melted (shorter than it used to be). When I burned up the piston a couple of years ago, this is what the plug looked like.

The plug on the other cylinder looks good.

 

[DevoMR]

Well a couple of things come to mind, 1 are the right plugs in and are they gapped correctly(to much too hot etc)? what side melted down the first time and this time? is the oil pump working to both sides? check tubing, and are the carbs running equally(is one leaner than the other?) have to take them apart to be sure. good luck, any more questions dont hesitate to ask.
ckoz

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I've got the right plugs, and they should be gapped properly. They are the same plugs I used all of last season. This was the first time out on the sled this year.

Both times it was the right-hand side cylinder that melted down.

As far as the oil pump goes, I don't know. Like I said, it ran last season with no problems, and my son drove it (very mellow) for about an hour before I hopped on. How can I tell if the oil pump is functioning properly? Maybe it is OK at lower speeds, but insufficient at high speeds?

Thanks for the response!

 

[jak_nelson]

You might want to pull the oil pump apart and clean out the passages. Also syncing the carbs might help. I dont know if being out of sync would cause your problem, but it is something to check.

 

[dbenney]

if im not mistakin a white plug means you are running LEAN! check the carb settings. if you gotta take it apart you might as well rebuild it anyway. also check the boots. not sure if you can on a sled, but i know on a car you can hear the detonation and thats bad for pistons.

 

[boondocker01]

A hole in the piston is dentonation it is caused by eather a dirty carb (lean) or ignition problems , check the carbs first

 

[adam_stallcop]

had the same thing happen on my rmk, the right carb had a plugged pilot jet.

 

[02summit800]

If it's the first run of the year, and you have signs for a lean cylinder, sounds to me like you have a plugged jet. My vote is to take the carbs out and check the jets.

 

[DevoMR]

Thanks for all of the help! I appreciate the responses and the info.

 

[APC]

Check the rubber boot between the carb and block. Make sure it's not dry rotted or the clamps are loose.

 

[MXZwithoutstuds]

I would sat deto is the right track but I have also seen this happen when the cyl head oring cracks. You get water blasting of the piston crown and thus thermal shock. Have a quick look at the orings and see if piston is clean as a whistle. If it is water has cleaned her up real well! lol

Jamie

I took my sled for a quick trip around the lake this weekend, and it died after about only 1/4 mile.

I was riding in about 8 inches of fresh snow, not going wide open (maybe 65 mph). I pulled the plugs and it looks like there is a hole in the top of one piston. The hole does not go all the way through, but its is definitely toast.

The sled was warmed up - my son had been riding it around for about an hour, never going more than 30 mph.

This is the second time this has happened to this sled. The first time I figured it was my fault since I was riding WFO in deep snow for several miles. But that was a couple of years and probably 700 miles ago.

If anyone has any ideas on what might be causing this, please let me know. I'm no mechanic by any means but I don't mind getting my hands dirty if I know what to look for.

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