Clutch side piston shattered. Lean condition

Sep 8, 2015
80
4
8
30
Having a lot of bad luck. About ready to just leave the sport and sit on the couch and watch movies on the weekend like a normal person. Had to prematurely rebuild my etec (thats another story) now a 140 miles later on my rebuild I had the left piston come apart, sent a pic to the shop that rebuilt it and he said it happened because that side was lean. I am disgusted, how does this even allowed to happen in an engine with not one but two EGT sensors!! There was never any alarms, trust me I was watching it like a hawk. If he is right, how did the computer not pick up on this and give warning ?
 
Sep 8, 2015
80
4
8
30
so sorry to be that guy but its a 800 etec out of a 15 summit, I know this is the 850 forum but the XM forum is dead. so far the game plan is, when I get another motor, take it to the dealer and have them hook it up to the computer before I even start it, have them start it and see whats up. the fuel injector on that side possibly has an issue, it was leaking gas when I was putting things back together, dont know if thats relevant or not, figured if there was actually something wrong with it I would either get a code or it would run shitty, neither of those happened. also sucks that it happened during a trip of course, miss out on epic Togwotee pow.

it was starting hard before this happened, not all the time but sometimes, I am just very disappointed in ski doo's computers not being able to catch this, this isint 2001 anymore....

would I have been able to see the danger coming with a heat gun?
 
Last edited:

Dynamo^Joe

Well-known member
Premium Member
Nov 26, 2007
1,073
965
113
Thunder Bay, ont
www.iBackshift.com
im not reading my resume, dont look at it like that. I clutched for an Acat factory racer from 95~2000. I spent a lot of time in the Cat factory and we had shop room classes on piston wash and then we had to go out and "tune" the engine to put carbon on the piston in the amount the lead tech wanted. Al Shimpa the lead tech started off the class with no words, just stood there [to get our attention] looking at us and said "Carbon sticks to a hot piston" and then said "repeat after me"..."Carbon sticks to a hot piston" and us students had to say it out loud. Al got us to Chant it out loud "carbon sticks to a hot piston" that was how our class started off. Every time you look at a piston you say to yourself "carbon sticks to a hot piston" and now can ask the question, how hot was the piston? You can tell by how much carbon is on it and how much the carbon propagated towards the edge of the piston.
Our objective was to run a 440 for 35 minutes full throttle (taped to the bar) in a 14 mile loop on a lake and average 104mph so that means the sled had to go 106mph at times to average 104mph and that meant "taped throttle open". When we blew an engine up, go back to the shop and pull out a top end from the crate, give the pistons to Al, put a new top end on and try not to blow up this time.
Top piston picture shows a piston that has not been heated enough to get carbon to propagate to the edge of the piston. The piston did not get hot from a lean condition.
The below piston picture is from my 872 after 800 miles with an AFR gage telling me im running average 12.4. The carbon has propagated to the edge of the piston but is thin on the edge. I have held that w.o.t for over a minute, loaded in fresh snow.
..............im going to put my head on the chopping block and declare your engine was not lean, not in the least. Im gonna take a guess and say the ring snagged and snapped off the top land width. The top land width is the thickness from the top of the piston to the roof of the ring groove.

Saying "lean" to me the speaker who uttered that is a liar.

RICH PISTON.jpg

Someone made me an offer for my 872 i could not refuse, so out it came. The 872 went out west and into a 174. The piston you see in the picture below, went right back into the 872 because there is nothing wrong with them. New wrist pin and needle bearing and that piston is still running today in the 872 out in WA.
AND to prove this even more, is my 872 had a 50/50 cylinder head but i ran it on 92 ethanol fuel and was able to do it because i had piggyback fuel injectors with a dobec controller and could control the fuel for every 1000 rpms. The point is the piston below has carbon on it because its running HOTTER than the piston in the top picture, but the piston below is NOT lean. It ran 12.4 average on AFR.

Miserwideopenmafia - sorry to see that kind of thing happen to you, but your engine was not lean, something happened to flick the piston material off and the root of the problem is something to do with the piston ring snagging the port or the port was modified to be able to impact the ring....its not fuel its a mechanical dimension problem.

"carbon sticks to a hot piston" and mister, your piston has little to no carbon on it, so it was not lean.
872 mag top.jpg
 
Last edited:
I would agree with Joe your sled was not lean the piston broke in the ring land I have seen it several times over years is Skidoo 800s
last one I seen break the sled have amout 5000 mountain miles quite a few for a pistons IMHO
I would also wounder about gas not being the quality it was supposed to be.
 

turboless terry

Well-known member
Premium Member
Jan 15, 2008
3,856
3,434
113
Big Timber, MT
so sorry to be that guy but its a 800 etec out of a 15 summit, I know this is the 850 forum but the XM forum is dead. so far the game plan is, when I get another motor, take it to the dealer and have them hook it up to the computer before I even start it, have them start it and see whats up. the fuel injector on that side possibly has an issue, it was leaking gas when I was putting things back together, dont know if thats relevant or not, figured if there was actually something wrong with it I would either get a code or it would run shitty, neither of those happened. also sucks that it happened during a trip of course, miss out on epic Togwotee pow.

it was starting hard before this happened, not all the time but sometimes, I am just very disappointed in ski doo's computers not being able to catch this, this isint 2001 anymore....

would I have been able to see the danger coming with a heat gun?
No worries. Was just curious. Didn't know if it was a turbo or regular 850. I was told it was a sad question and turns out it's an 800. Who looks sad now. Hope you get it figured out. You can quit on the sled but don't quit on the sport.
 

Dynamo^Joe

Well-known member
Premium Member
Nov 26, 2007
1,073
965
113
Thunder Bay, ont
www.iBackshift.com
piston_wash_2.jpg

Bottom here is from an Acat race handbook. you made photocopies of this page, hole punch then into a "piston wash binder". This is like from mid~late 90's. no digital cameras back then, haha. You take the piston and put it upside down on the page. then trace around with a pencil. then go out and do your running and after pull the head off to look at the piston, you drew out what the wash looked like, before, after, etc. the bottom of the page is what you were looking for on the right (3rd piston picture) This was the year after i was done at Cat, and testing on 440 mxzx x-country sleds.
Jetting..piston wash.jpg
 

Skidoox

Well-known member
Lifetime Membership
Sep 4, 2001
21,891
36,870
113
Provo, UT
1614187331418.png
Is the locator pin pushed into the piston? It looks like the ring spun until it found the port and then broke the top of the piston off.
 

sledhead_24_7

Well-known member
Lifetime Membership
Premium Member
Jul 30, 2008
2,351
787
113
Jackson Wy
Since that motor has been down 2 times. Which is 2 times too many.

For a replacement I’d seriously consider a short block from Skidoo. Everything internally is new. Bolt on old head, electronics, injectors, and go.

Plus 1 year warranty on new engine


Sent from my iPhone using Tapatalk
 
Sep 8, 2015
80
4
8
30
I know that the overwhelming majority says it was not lean, maybe that's true, but allow me to play devil's advocate. If it was not lean then why was there carbon on the piston that did not go, I did not mention this before yet but there was also scarring in the good cylinder aswell, also it was starting very hard when warm prior to this happening. I just want to challenge the 'not lean' statement because it seems the other cylinder was on its way out. Even if it was not lean I am going to treat it as it was to possibly prevent it from happening again. going to take it to the dealer and have them hook it up to the computer for the first start and see if things are legit. While its there prolly gonna see if they will buy it off me so I can either get an 850 next year or nothing at all, chances are I will be taking it back home tho.
 
Sep 8, 2015
80
4
8
30
Since that motor has been down 2 times. Which is 2 times too many.

For a replacement I’d seriously consider a short block from Skidoo. Everything internally is new. Bolt on old head, electronics, injectors, and go.

Plus 1 year warranty on new engine


Sent from my iPhone using Tapatalk
its actually the first time, I originally had it rebuilt because I had an exhaust bolt come out of the Y pipe and get wedged between the clutch, ended up putting a 1/4 inch hole in the crankcase. also the shop said they would rebuild this for free, they admit no fault tho, basically said they are doing it because they feel bad for me, you can make of that what you want.
 
Premium Features