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Chipped Piston and Engine Rebuild Opinions

6K views 16 replies 4 participants last post by  kccats 
#1 ·
I am tearing apart a 08 summit 800 engine for a new top end. There is a little chunk missing from the top of the piston and i am wondering if there is any way the shrapnel could've entered the crank case. I know that if the piston skirt blows apart it needs to be cleaned out, but this seems more specific to the top end. Do I need take the engine all the way apart and clean the bottom out or can i get away with just a top end rebuild. Honestly i should probably get down in there and re-grease the crank bearings and replace the seals because its a new sled to me and has 3000 miles on it but i want to know if top end only is even an option with this kind of damage.
Also the piston walls were scratched up. I'm assuming they need to be replaced but any opinions there would be appreciated as well.
 

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#2 ·
If you can catch your fingernail on the scratches then it needs to be replated.
If not then just give it a quick hone.
Since the chunck is from the top of the piston it is likely that none went into the base.
Check the VES that it is not damaged too.
 
#3 ·
Welcome!
I would go ahead and take the jugs off and inspect the crank for any signs of anything? Blueing scratches rough spots, etc

I can help you with pistons and gaskets when you are ready.
But check the jugs and make sure there isn't more damage than you can see!
Next is WHY did the piston chip?
 
#4 ·
Thanks for the comments. Its good to know I don't need to pull the entire engine to clean it out. Feels like a daunting task. So a piston breaking apart like that is more than just regular wear and tear? I didn't think of that. What might be some of the potential causes? overheating? A particle entering the cylinder?
As long as i have it apart would it be too hard to re-grease the outer crank bearing while i'm at it or would that require pulling the engine. I don't have a clutch puller yet so i cant really see what that would entail.
 
#6 ·
After a second look at the pics, what I see is over heating causing the piston to fracture.
How does the plug from that cylinder look, is it gray/white?

That is also the clutch side of the engine?
If so, that is pointing to a leak in the crank seal and since it is the 800 you should definitely tear it all the way down and have the case halves checked for wear.
 
#7 ·
The broken cylinder that is chipped is not the clutch side cylinder. The spark plug was normal colored however I believe the engine was started a few short times since it blew so that might be a ruined clue... I still need to get the jugs off and inspect them. I quit when i got the heads off cause it was 2 in the morning and freezing cold, I haven't got a chance to finish the job... need to do it soon though. I want to get parts figured out and on the way for this project... I'll post some more pictures and questions when i get them off.
 
#8 ·
A better close up of the piston showing the broken edge can help with diagnosis though.
The surface of the metal at the break can point to what was the cause.

Try to get the shots as brightly lit as possible too.
 
#10 ·
Alright! After several tedious hours I finally got the Jugs pulled. I really wish I knew there was a wire clipped to the far side of the non clutch side carb before i started... would've made the whole thing much easier. Here are some pictures of the internal damage. I'm wondering what's normal and what is abnormal.
Not sure if these are going to upload... Let me know if the pictures don't work out.





 
#13 ·
Dang it. This is the third time I’ve re written this and now I’m doing it in word because It keeps erasing when I try to post.
I went out and checked the crank and can’t see any lines out of the ordinary. Am I looking for wear lines? Marked Lines? The bottom if the engine is still in the snowmobile so I can’t see the entire crank. Where should I be looking?
On another note, I bought this machine without the budget to get parts, but in a couple weeks when I do, the plan is to get new pistons, a core swap on the jugs, get a clutch puller and check the clutch side seal, replace that if needed and call it good. I figure that should be enough to last me through the season. I’m getting jumpy to have it running since we have decent snow now. Also, I can’t decide if there is going to be any real difference between OEM, something cheap like pro x, or something nicer like the mcb piston kits on the pistons, any suggestions there would be great.
 
#15 ·
That's pretty good for the jugs. I can't really tell where to take it to have it done. From my search online it seems like a pretty difficult process so i'm going to have to ship the jugs somewhere to have them done. And most of those companies seem to prefer a core swap to speed things up. Looks like it ends up being about $220.
Is replating something a local machine shop or engine repair shop could do? I haven't even called up my ski doo dealership yet.
 
#16 ·
Replating is a specialty shop thing. Two very good companies are US Chrome and Millennium Technologies. If you want your cylinders back instead of ones they have already ready to go, you can send them your jugs and new pistons and they will set the ring gap. That saves you a step.
 
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