So out riding just some simple trails making sure my snowmobile is ready to go this year. Its an 03 Mountain Cat w/ an 825 motor with half a season on the motor. So i get about 6 miles down and and we pull over for a second. Im checking everything out and there is some oil coming out from around my spark plugs. Well they came loose some how so I tighten them down (snug then about a 1/4 turn) So about another 7 miles down the road about 80% throttle it pops real bad keeps going then pops again and dies. I pull the hood off and low and behold the clutch side cylinder spark plug has about a thread left before it is all the way out. It wont run but still has compression. Anyways get towed 13 miles back put it on the trailer get home take the domes off and there it is a dime size hole and chunks missing on the intake side on the piston. The only thing I can get at is that it started drawing air in from around the threads and leaned out pretty bad. The piston is toast but the jug walls seem to be okay and it gets inspected tomorrow. It just sucks already first ride of the season and one small mis-hap sets me back a lot. Anyways just a bad story thought I would share my frustration. Anyone had this happen on any of the sleds before in the past?
Melted Piston!!!
- Thread starter eric_dorr
- Start date
Stuck riding the back-up sled this year!
At least you got out and rode a few miles! I just installed an 860 kit in mine and was unaware of pistons could be installed backwards. I didn't even make it onto the trailer. I was also able to save my jug, but I have to have my crank re-done and purchase a new crank case and pistons
I feel your pain!!
At least you got out and rode a few miles! I just installed an 860 kit in mine and was unaware of pistons could be installed backwards. I didn't even make it onto the trailer. I was also able to save my jug, but I have to have my crank re-done and purchase a new crank case and pistons
I feel your pain!!
At least you got out and rode a few miles! I just installed an 860 kit in mine and was unaware of pistons could be installed backwards. I didn't even make it onto the trailer. I was also able to save my jug, but I have to have my crank re-done and purchase a new crank case and pistons
I feel your pain!!
Thats sucks bad man yeah I got a buddy here with a lot of arctic cat parts like alot lol but he happens to have a spare 825 Jug, Piston and Dome. And well its free cause he feels bad about the situation. So I lucked out..
Yeah man I dont know the carbs will obviously be gone through while the motor is apart so if thats the culprit then it will be attended to now!!
Loose spark plugs usually mean detonation. Old fuel? Any changes made to motor over the off season? Timing advance? I would try to find the cause so your next ride out does not end the same way.
7
76FOMOCO
Well-known member
we have a winner!!
loose plugs = det!
bad gas or to much comp and or timing for the fuel.
was there little white dots all around the edge of the piston?
welcome to deto!!!
I am sure you did not have any old fuel in it...........RIGHT?
I am sure you did not have any old fuel in it...........RIGHT?
Yeah Not bad gas brand new 12 gallons and no there are no white spots around the edge of the piston would a picture help.. No changes to the motor at all. I just hope I didnt overlook snug up the spark plugs when I changed my dome o-rings a week ago. I prolly did and after 12 miles of riding they rattled themselves loose and drew in cold air. Well really cold air it was
-10 when we got out of the truck and doing about 60 or so when the motor went so I was told that would do it. Air drawing into the combustion chamber without any fuel to mix with it..
piston problems
one thing to consider, in your initial statement you said you only ran it a few times last year, was that in the spring when it was warm out, now its very cold you will need to jet up 2-3 sizes to compensate for air temp. and help cool the burn.
one thing to consider, in your initial statement you said you only ran it a few times last year, was that in the spring when it was warm out, now its very cold you will need to jet up 2-3 sizes to compensate for air temp. and help cool the burn.
Loose plugs did not draw in air and ruin your engine IMO.
Only thing that would happen is you would loose a plug and possibly tear up the threads.
You have a lean/deto issue.
Could be lean, too much compression for the fuel, timing, etc.
You said you replaced the dome O-rings... Was the cooling system completely purged?
Goos seal on the heads?
It is very easy to get air trapped in the system after a repair.
Post some pics of your pistons... You have more going on them just forgetting to tighten your plugs.
Only thing that would happen is you would loose a plug and possibly tear up the threads.
You have a lean/deto issue.
Could be lean, too much compression for the fuel, timing, etc.
You said you replaced the dome O-rings... Was the cooling system completely purged?
Goos seal on the heads?
It is very easy to get air trapped in the system after a repair.
Post some pics of your pistons... You have more going on them just forgetting to tighten your plugs.
Here are some pics of the Melt Down!!!
And yeah I Know that it was purged I worked on it for awhile just to make sure.. The overflow bottle had great pressure and when I pulled the domes off to inspect the piston there was still a good amount of pressure in the jugs!!
Here are some pics of the Melt Down!!!
Deffinatly deto. (imo) Too much timing or too high of compression. Cold temps may have made it worse, but the problem was there. You need to run some better fuel or back off timing and/or lower your compression or you will be posting more pics just like those.
So why wouldnt the other piston show signs of deto if it was gas. It was just 92 octane with 32:1 oil mixture..
what elevation, what jet size did you have in there??
Plugged jet?
Bad crank seal?
Bad crank seal?
