Question for the expert transmission rebuilders

[cdn280]

I've got the cases split on my 2006 300EC and will be replacing the 2 bearings on the transmission shaft that holds the clutch. Both bearings, an open 6203 and a sealed 1 side 6205 are both a bit gritty feeling, so I have 2 new very smooth running SKF bearings to pop it.
The 6205 I took out had one rubber seal on the clutch side that didn't look in very good shape, much like what a cheap chinese wheel bearing looks like when its toast. (like rust bubbling the rubber) There is no seal on the trans side. In theory this seal wouldn't let much if any oil through it to the clutch side. I have a doubled shielded (metal) one to replace it. This will likely let some oil pass through it, especially if I take off the trans side shield like the oem one.
My questions are:
Should I leave the trans side shield on it to keep out any tiny metal bits that could get in and cause the bearing to get rough again?
Is there any reason why no oil should be allowed to pass thru that bearing to the clutch? (sealed vs shielded) Seems like squeeling clutch problems are fixed by more oiling. (like drilling the basket to let more oil in)

[cdn280]

Here is a pic of the over heated, or rust bubbled looking shield.

[stainlesscycle]

the seal is there to help keep oil flowing through the hole at bottom of the case, not through the back of clutch (but the clutch basket spacer should stop flow almost as much as a shield would). the clutch picks up oil as it spins, i wouldn't think you'd want to pull oil from the trans through the clutch center..

i would use a 1rs bearing, not a zz - if you're gonna use the zz - i would pull the shield on the trans side - shielded bearings definitely spin with less resistance, but shielded bearing failure is more likely catastrophic - sealed is not....

definitely skf/fag/koyo/nachi etc. no junk bearings...all those trans bearings can be c1 also - only need c3 on the crank.


i don't think this really answered your question.....

[GMP]

I've rebuilt a couple 250 GG motors and a 125, and none had sealed or shielded mainshaft bearings. I don't remember them in the Jap bikes I've done either. I replaced with the same, SKF C3 clearance spec.

Lube in a 2 stroke trans is mostly chaos, just splashing and scavaging from gravity. I doubt there is any significant flow through that bearing, especially when spinning.

[cdn280]

Thanks guys. I thought the same thing about the clutch spacer slowing any direct flow through the bearing, especially since its just getting splashed and dragged around in there as you said. I can't recall seeing a seal on that bearing in any other motors I've had apart so hopefully its a case of it really doesn't matter, as long as theres a bearing and some kind of oil supply. Wouldn't be surprised if they use whatever is on the shelf at the time !
I'll go half way and use the ZZ bearing with the trans side shield removed.
Would be a good design excercise question ... maybe the guys with squealing or slipping clutches don't have a seal there ??
Because the bearings I'm replacing have a bit of a knotchy feel to them, think I'll add a second magnet drain plug in the oil fill hole too. My newest trials bike came with 2 magnet plugs. My previous one didn't, so can't hurt.

[gasser]

Originally Posted by cdn280

think I'll add a second magnet drain plug in the oil fill hole too. My newest trials bike came with 2 magnet plugs. My previous one didn't, so can't hurt.

The factory should do this on all new bikes so you can swap them out if the drain plug gets buggered.