Rebuilding 800 Etec topend

[new24stroke]

Hi
im helping a buddy rebuild the topend of his sled. It’s got one bad piston. I’m just trying to see what would have cause this. He was running straight avgas. You can now rock the piston back and forth in the cylinder , also some scoring in the cylinder The other one is tight like it should be.

 

[NoBrakes!]

Why av gas?

 

[slededjr]

Hi
im helping a buddy rebuild the topend of his sled. It’s got one bad piston. I’m just trying to see what would have cause this. He was running straight avgas. You can now rock the piston back and forth in the cylinder , also some scoring in the cylinder The other one is tight like it should be.

Any mods done to it?
Which cylinder?
Any pics?
Could be a number of things, hard to say without seeing.

 

[neilsleder]

Yah pull the piston and post pictures of it. Pistons can tell the story of what’s wrong

 

[Luke The Drifter]

Which side has the bad piston? How many KMs?

 

[new24stroke]

About 2500 on. Right side. No mods

 

[new24stroke]

When I drained the coolant there may have been 2-3 Litres of coolant

 

[pfi572]

Looks like intake side or is piston scored all the way around ?

 

[new24stroke]

Both sides are scored. But more so on the intake side

 

[slededjr]

Both sides are scored. But more so on the intake side

Snow ingestion, lack of lube.
pic of exhaust side?
pics of pto piston too.

 

[new24stroke]

PTO side looked good. Still had good compression 125 psi. I will get some pictures in a couple days. I don’t have them on my phone

 

[new24stroke]

One other thing I should mention is my buddy did drive this out of the mountains for 50 km with the blown piston.

 

[Poleman]

One other thing I should mention is my buddy did drive this out of the mountains for 50 km with the blown piston.

Given that you better tear the bottom end apart too.

 

[fredw]

had a boosted 800 etec impulse go down after 3400kms running strait av gas from day one this spring, was lean and det took it down from what we could tell on mag side.. lots of 10 lbs boost over the years and been running good since then, cost me a set of new jugs, never touched bottom end and run out .002.. replaced fuel filter, checked fuel pressure and good from what we could tell..i was going to replace pistons at 3k and will do that from now on.. ****happens

 

[new24stroke]

Here are some better pictures

 

[new24stroke]

 

[new24stroke]

This is the pto side it looks good

 

[new24stroke]

So it was pointed out to me that there are 2 cracks by the exhaust port. Also my buddy told me he was adding coolant every other ride.

 

[pfi572]

So it was pointed out to me that there are 2 cracks by the exhaust port. Also my buddy told me he was adding coolant every other ride.

Yep , most of the time they crack in this area when tightened up .
Have had rebuilt cylinders leak after being repaired as well .
Which sucks as it’s really hard to find or see until you fire it up and have antifreeze leaking into exhaust.
Tear all back down again .