Any idea on what could have caused this catastrophic failure?

[debun]

I recently replaced the bearing on my motocross bike (Suzuki RM 125) The bearing has 9 hours of use on it and it blew up. The bearing is in the transmission and supports the left hand side of the counter shaft. It's a wet clutch and the oil that lubricates the clutch plates also lubricates this bearing. The OE bearing is a 6003 17 X 35 X 10

I have never seen a bearing failure like this in my life. It was a Chinese bearing (which many are now). I'm suspecting debris but that still shouldn't cause the bearing to grenade like it did. The other difference from OE is this was a CN clearance and OE likely C3 (CN is from 3-18um and C3 is 9-25um). Could the temper be wrong? Dirty steel? What are your thought?

 

[Tmoose]

I'm sorry for your problem.

Not much to work with.

I'd rinse of the pieces to get a better look at the working surfaces on the races, and the fracture surfaces on the broken races, and wear on the cage/retainer.

==================

Why, and how was the bearing changed?

 

[Cierva]

First comment: dont buy cheap Chinese bearings. Stick to established western world manufacturers like SKF, KOYO, FAG, NTN, NSK. If OE was C3 (and it likely was) theres a reason for it. Make sure shaft and housing are in good condition, still within tolerance and finish smooth. When you assemble make sure bearings are fitted properly.....no misalignment. Impossible to determine failure mode without seeing the pieces.

 

[MikeHalloran]

Nine hours is a _lot_ of motocross.

Replace the new bearing after four.

Consider having a dealer do it, at least once.
... and show him the pieces of the grenaded bearing, even if you don't post photos here. (I wish you would.)

Use the factory tools and procedures and parts.





Mike Halloran
Pembroke Pines, FL, USA

 

[debun]

The really isn't much to tell from the races since they are scoured. As for Chinese bearings even SKF, INA etc are all manufacturing in China albeit this is a brand I have never used before. In my forensic exercise I discovered it was a CN clearance not sure what OE is but I suspect it might be a C3. The supplier I bought the bearing from said he has sold thousands of them and never seen a failure like that in any bearing he has ever sold. Seems to be a mystery.

 

[romke]

it looks like the failure was quite sudden - the debris show no signs of long term overheating in the form of laquer or a brownish coloration. the most likely cause then would be some foreign object that got trapped between balls and races where of course there is very little room for it.

have you closely inspected all the debris and maybe found something that might have come from the bearing itself or are there any parts (spacers, washers. fasteners etc) that seem to be missing from the surrounding gearbox?

do you have any more photographs?

 

[Tmoose]

Why, and how was the bearing changed?

regards,

Dan T

 

[Cierva]

I’m back. Sorry I did not diagnose your problem but you have provided the information required. I have seen this failure many times.
Let us assume that you have installed the bearing correctly with no installation damage.

Failure Mode:
After a couple of brmm brumms you are off on an hours moto cross.
Work is being done by the engine and thru the gears of which a byproduct is heat.
The shaft convects the heat to the bearing and ball set that also heats up and expands. The bearing outer ring (OR) is in a large aluminum housing which is a great big heat sink. It is also air cooled. The result is the inner ring and ball set expand at a faster rate than the OR and will quickly eliminate the internal clearance (IRC). Further expansion will internally preload the bearing, forcing the balls into the OR and rapidly increasing heat in the bearing further. Ultimately the IR and ball set, in effect become a crude clutch and grab the OR. With 28kW of power driving the assembly, something’s gotta give, and thus your bearing failure .

The OE was a C3 bearing which is there to provide extra clearance at a time of differential expansion.

The retail outlet that provided you with a CN bearing probably didn’t have a C3, and may have commented ”there’s little difference”. That’s OK for a skateboard, but not for a motorcycle and 28kW.

 

[debun]

I did not see any discoloration in the race pieces. The differential heat theory sounds plausible but it's in an oil bath so I would suspect uniform heat across the bearing assembly. I was thinking incorrect temper. Does anyone know how hard you can get 52100 after quench?

 

[Cierva]

Rings are hardened and annealed to obtain hardness 57 ~ 64 HRC.
Balls are hardened 63~66 HRC.
Bearing hardness has nothing to do with your problem.
The inner ring and ball set is being heated and expanded in diameter at a faster rate than the outer ring, which is mounted in a gigantic air cooled heat sink. There is a temperature gradient across the bearing that is greater than the CN bearing can handle. Hence the OE specifies C3.

Your bearing failure is not unique, and in fact is a classic failure mode that any bearing expert would quickly recognise.

Rebuild your engine with a 6203C3 from any reputable western world manufacturer and your problem will disappear. Having said that, what caused you to replace the bearing that preceded the CN bearing.

 

[geesamand]

"The really isn't much to tell from the races since they are scoured. As for Chinese bearings even SKF, INA etc are all manufacturing in China albeit this is a brand I have never used before. In my forensic exercise I discovered it was a CN clearance not sure what OE is but I suspect it might be a C3. The supplier I bought the bearing from said he has sold thousands of them and never seen a failure like that in any bearing he has ever sold. Seems to be a mystery."

Chinese manufacturers make the entire gamut from world-class bearings to complete junk. When someone states that a bearing is made in China, they have wasted their breath as it means nothing.

 

[debun]

Cierva according to SKF CN is for normal use

http://www.skf.com/us/products/bear...ecifics/bearing-internal-clearance/index.html

. The OE bearing was only marked as 6003 hence I went with a CN clearance. I know that you can have failures with excessive clearance as well. I think this time around I'll just order the OE bearing.

 

[Cierva]

Sorry ... 6003 but all comments remain the same. Good luck ... Cierva

 

[Panther140]

Suzuki Gearbox lasting 9 hours? Thats impressive. What's your secret? haha

Anyways, why did you rebuild the transmission in the first place? Anything less than perfect happen when you were putting the cases back together? What kind of oil are you using (ATF is the best for these wet clutch trannys)



"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[Tmoose]

OP said "The OE bearing was only marked as 6003"

By chance is the old bearing still around?


Could you post pictures of both sides of the races?