Fresh motor failure? What’s causes this ?

[bathtub28]

Fresh motor rebuilt from crank up, maybe 50 km . Used pre mix for breaking in, ran amazing till it died .
Lean?
Debris?
I’ll be pulling it apart next week but not sure what to watch for in the repair .

 

[CatMan16]

Are the rings still intact?

 

[bathtub28]

rings look fine but the c clips holding the wrist pins look broken. The kind that don’t use snap ring pliers . Could that material make its way up to the top?

 

[Trashy]

I had an 04 Rev and when the crank failed, I removed the top end and it pretty much looked like your pics

 

[CatMan16]

That is the way that style off clips looks. There would be some major scoring in the cylinders to have any parts of those clips get above the rings. I think the debris is from the piston chipping. Looks like it may have been too lean or too hot or both. What color were the spark plug tips?

 

[imdoo'n]

what was the reason for the rebuild, and who did the rebuild?

 

[bathtub28]

Bought the sled as fixer. The mag side piston was cooked, same damage except the piston was a lot worse , I think cause buddy kept running it on one cylinder (pto side ) took the whole motor down , sent out for cleaning , new crank seals gaskets pistons , carb rebuilt and set to factory. Was running REALLY good for the start and then died.

 

[bathtub28]

Also some scoring in the mag side cylinder

exhaust side

 

[bathtub28]

Took carb back apart and it has 240 main in it and spec says 280 , looks like I missed that. Someone along the way must’ve got her leaned out I guess .

 

[cdnrock]

Broken roller bearings . When you installed the primary clutch did you use an impact gun ?

 

[Dazzler]

Took carb back apart and it has 240 main in it and spec says 280 , looks like I missed that. Someone along the way must’ve got her leaned out I guess .

Check the carb boots as well for cracks etc, if they're leaking/sucking air, that will lean it out as well. Between carb boots and crank seals they are usually the demise of older been sitting in the corner for years, two strokes.

 

[CatMan16]

Took carb back apart and it has 240 main in it and spec says 280 , looks like I missed that. Someone along the way must’ve got her leaned out I guess .

This would explain the running really well part before it quit. When a carbed machine seems to be running better than normal there is a good chance it is running lean.

 

[bathtub28]

That’s what I’m thinking , ran better than it seemed it should, ( too good to be true) carb boots good fresh crank seals, I think it just leaned right out

 

[Ronaha]

What was the temperature when running it, they run leaner in the cold and richer in warm....id just hoan and slap some eBay Pistons back iner lol.....I've done way worse!

 

[bathtub28]

General majority seems to be c clip failed. Was running on a nice day, -5-7, got some parts ordered, give it another go, hope to learn from mistakes.

 

[KatMan]

Do you normally right at the same altitude? Regardless. Buy 5 mains jets larger than the one that was in there.(ones that will make it run richer) Start with the one that will make your sled run the richest. If it you can get rpms with that one, get more jets that will make it run richer. And start with those till you get it to bog/flood. If you can’t get it to get up to rpm(it bogs and floods) move to the next smaller jet and repeat. Keep going till you can get your revs up. That will be the safest jet you can use. May be hard on plugs and start bogging at higher altitudes. You can go to a less rich jet at that time if you want.

this should compensate for any air leaks that may be leaning it out as well.

 

[kenvb]

did you split the cases and wash everything out from the last time the motor went,small pieces of metal stay in crevices in bottom end,, that is big mistake people make when rebuilding a motor..dont clean out the bottom end, i am guilty of this too. never again ,always take engine down to the crank.clean everything.

 

[bathtub28]

Top half of case . Is this hooped? Some definite pitting.

 

[bathtub28]

Also, this is not the same motor that failed , it’s a parts motor that I’m seeing what is usable from

 

[Lund]

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Top half of case . Is this hooped? Some definite pitting.

That is a typical ROTAX casting, very porous, i have seen even Rotax heads like that after shaving them, so no it is not unusual for Rotax.
Can you use it, YES.
What you want to do is loc-tite the mains bearing's with 638 green during the assembly process. The holes in the center of each bearing seat are just pin retainer holes to prevent the outer race from turning, there will be a pin at each bearing. It is common for that pin to shear, if it is missing the bearing is no good. The groove cut in the seat acts as a guide to keep the bearing aligned and keeps the crank from separating. You will find a ring wrapped around the bearing, kinda like a big snap ring with no eye.
What is important to look for is the line bore, is it true and straight and even more important "CHATTER" marking's on the surface of the bearing seats. Any chatter marks or signs of a bearing moving in the case means the case is no good.
Looking at your pictures i see very little evidence of chatter but enough that i would loc-tite the bearing in place to help fill any imperfection's.
So ya, nothing wrong with the case other then its a typical Rotax.