Counter balance bearing failure

[grizztracks]

Working on a 2009 Nytro that developed a knock while running down a trail at 50 mph. Engine has around 5000 miles and seemed to be well maintained. The knock started with no warning of any problems. No codes displayed and the engine did not shut down due to low oil pressure. Metal shavings were found inside the oil filter so the motor was brought to me for repairs. With the sump cover removed I found large shavings which appeared to be to large to be related to a crank or rod bearing failure so pulled the stator cover and discovered that the counter balance bearing had completely blown apart. Seems like a strange bearing failure seeing how there is minimal stress on that bearing. The bearing race doesn't show any signs of being overheated due to lack of oil so I'd say this engine had a defective bearing from the factory.

 

[74Nitro]

Any signs of rust of the bearing?

 

[grizztracks]

Any signs of rust of the bearing?

No rust. If moisture was present you'd probably see it in the oil and other locations in the engine. The internal parts in the engine are clean. Checked the crank and rod bearing and they look good.

 

[74Nitro]

Hopefully none of those scrap pieces damaged any teeth on the crank gear. I know from past experience on ATV's I repaired, that any knicks, or even the slightest damage in the teeth can make some awful loud noises when the engine is back and running.

 

[grizztracks]

The counter shaft drive gears don't look to bad. There is a small amount of damage in the crankcase from the shaft weight hitting but I don't believe it anything to be overly concerned about.

 

[Gone Blue]

Wow, that bearing produced lots of metal shavings. G.B.

 

[grizztracks]

Wow, that bearing produced lots of metal shavings. G.B.

I believe most of the shavings are from the inner bearing cage but I can't account for all the balls that completely fell out of the bearing. I might have recovered 5 or 6 of them and a couple larger sections of the cage so the rest of the balls must have been chewed up possibly before it started to knock. I find it hard to believe they got chewed up without damaging anything else but most all the shavings are metallic and I'm not finding any other damage.

You can see on the inside of the crankcase where the balls pushed out of the bearing race. I don't think the case damage is bad enough to worry about and a new bearing should install properly with no additional concerns.

 

[1nc 2000]

My nytro failed like this on the second year but it also chewed up the gears from the balance shaft bouncing around and blew a hole in the front of the engine about the size of a softball from a mass migration of parts.
It was covered under warranty with one of the complete crate engines they had here for the snow cross team.
Dealer had it back to me running in about 2 weeks.
I would check those gears closely for cracks.

 

[grizztracks]

I did a quick inspection of the counter shaft drive gears and did not see a problem but I'll look at them closer when I clean all the parts and flush the engine block.

 

[grizztracks]

Back together.

 

[4strokes]

got one going on the bench today. was brought to me for a starter failure. they forgot to tell me it has been running on 2 for some time. center rod must be thrown and happened to hit the crank when trying to start it. should be a good one. was told it ran great