Bearing help

[Big Scotty]

G'day
I'm rebuilding my 125 and the bearings I have got for the crank have plastic cages instead of steel,my question is has anybody used these type of bearings and have there been any problems,these bearings have a c4 high speed rating,any help appreciated
Cheers scotty.

[Lozza]

They are called polmide cages , they are standard fit on many high spec machines. Had more problems with riveted steel cages than polmide cages. C4 is not 'high speed' just refers to the amount of radial clearence inside the bearing. 

[oldyzman]

WASP - How do you turn them into C4.... Has C4 got more clearance than C3
Brett

[grouty]

Not knowing much about the different cages on bearings I brushed up a bit while rebuilding the L/H main on the old KLX250. The originals had steel cages. The new ones have plastic. It seems that some manufacturers today use them in preference to steel because if they start to break up, the plastic does "less" damage to the internals as it munches it's way through.
I am still not convinced ! But they are holding up just fine.
I don't know too much about the clearances, except that I fitted C3 to the engine. As I understand C2 has very fine clearances for slow moving shafts. C3 has a bit more, and C4 more still and designed for very fast rotating shafts.

[Big Scotty]

G'day
Well the engines going back together this weekend complete with plastic caged bearings, spoke to a few reps from bearing shops and they all said they should be okay,shall give a report how they go,might be the secret edge I need.
Scotty

[OverTheHill]

Always used C4 fibre  caged bearings in our buckets & [YZ125G days by memory]. I'm sure we were told that fibre cages were for high speed [& hell we were fast--i think!!]. Don't think i ever had a good steel cage give up in use but the thought was always there. Had a few ally big end cages break up in our honda 125 4stroke bucket days & have an xl185 motor which i crowded the big end rollers [no cage], mainly because i was too tight to buy a cage but remember my bsa B33 big end replacement coming with crowded rollers--actually i think i used a cage & took half the rollers out. Bugger, now i'm worried about the 185.

[Lozza]

G'day
Well the engines going back together this weekend complete with plastic caged bearings, spoke to a few reps from bearing shops and they all said they should be okay,shall give a report how they go,might be the secret edge I need.
Scotty

Unless you rev your engine to 20,000 rpm or have them fitted as standard they don't make much difference. Like an Aprilia RS125 or a Rotax Max kart engine will last 100km before a C3 cries enough.

Crowded rollers Morley no wonder it failed 

[OverTheHill]

Lozza, [trying to think], it was the cage breaking on the xl125s bucket racer that used to bring those motors to a halt, but crowded rollers on the 185 are still spinning [mind you only occasionally] on a dirt bike. 185's only single rollers where the B33 had two rows of 1/4x1/4's skidding end on & side on. Did use it like that but next time went back to a cage [on BSA that is]. Cheers.
ps, on the 185 i used a damaged cage & cut the end bits off then filed them up for washers to keep the rollers secured end on as they would be when fitted in the cage. Also, bottom line probably was--didn't have a cage & wanted to get it running for the next day [or something equally as stupid for an excuse]