which bearings go first?

[rd400canuck]

Hey guys,

I was getting ready to pack up my RD400 crank to send off for rebuild and was spinning the bearings with my finger one by one and all 4 of them seem fine to me now. I was sure when i first took the crank out the 2 center ones spun a little freely for my tastes so thats when i decided it needed a rebuild. Now.. they all seem fine, I dont get it.

Do the centers usually go first? I would have imagined the outters go first... also... should i try to wash the bearings free of oil to see if they are indeed loose like i thought they were?

I'm now thinking this crank is in good shape for at least a summer. There is very little side to side play of small ends, also.

[2 Stroke Jamoke]

I would definitely wash them out with some brake clean or mineral spirits. You will get a better idea what condition the bearings are in when they are oil free. You can easily throw some outer bearings on there if you are inclined. The big end on the rod should be inspected closely,  I think they are the first to go.

[SUPERTUNE]

Always pull off the outer bearings and do a crank true, and new outer main bearings.
Always check rods bearings for wear by measuring rod side play and deflection.
If good, check center bearings for wear and roughness.
A true and new outer bearings are usually good at about 10,000 miles.
Anything up about 15,000 up is mandatory for a full rebuild!
IMO.
Chuck

[rd400canuck]

Hmmm...  I'm so tempted to run this crank for a summer. I think i'll get a dial gauge and check run out. If it's ok i'll replace the outter bearings and run it. they feel the slightest bit suspect to me. The middles seem smooth as glass.

[rd400canuck]

I just bit the bullet and sent the crank out for rebuild. They quoted me $500 for rebuild but I have 2 new con rod assys that I sent with it. Hopefully they dont take exception to this because I guess essentially they'd be losing some money on the job not providing the rods themselves.

[2 Stroke Jamoke]

Hey! You need to source some rm125 big ends or rg500 big end bearings. Big upgrade,  they have 3 more rollers than stock and will keep the big end pin from "octogoning" Chuck can chime in with the part number but if you are rebuilding the crank you should definitely do this mod!

[rd400canuck]

I'll email the shop doing the work and see if it's a possibility for them to source RM125 bearings.  Its the prox kits I sent with the crank.... are the rm125's still better?

Is it just the bearing that is different... more roller pins in them?

[2 Stroke Jamoke]

Yea the prox rods are great I have them in my rd400, but the rm125/rg500 bearing is better. Less cage more bearing. I think the prox and stock rd ones are 14 rollers, the rm one is 17 rollers. Better all around, and if you are rebuilding it you should definitely go for this upgrade.  You can rev it higher and it's more insurance for those missed shifts and hard runs.

[2 Stroke Jamoke]

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F202469102957

Here are a couple on ebay I found.

[rd400canuck]

I think for the added cost of the two bearings and my intended use of the motor (100% stock motor/intake/exhaust) I'll go with the prox bearings. With stock powerband I definitely wont be revving the snot out of this bike. I dont even think in stock form this bike can even rev that high. Arent they more low/mid oriented? My RD400G certainly was once i put it all back to stock. On the next crank rebuild I'll do the mod though.

Thanks again guys :)

[rd400canuck]

one more bearing question....

The needle bearings on my gear assy seem not to be smooth. The ball bearing ones are perfect though. Anyone got experience with these things? Do they go? When i spin one of the gear assys by hand, while its in the cases but one is removed, I can definitely hear noise but I'm not sure what it's coming from... I'm wondering if it's these needle bearings.

[rd400canuck]

nevermind!

I held the shaft by the needle bearing in my hand and spun the gears... and it was far from smooth. Looks like I need to make another order with econocycle soon.