Putting a gxp crank in a bb90 shimano bottom bracket - best way?

[alcatraz]

Hey WWs

A friend's trek domane with bb90 is being upgraded from ultegra to sram red and we've come to the crank now.

I installed the bb a few months ago so I know exactly what it is. It's NTN 6805 bearings with 25mm inner diameter and then there is a plastic insert that makes them 24mm.

What would be a light solution here? Has anyone tried putting a 24/22 mm reducer insert in an existing 25/24mm insert? Does it really work?

How hard is it to find a single gxp left bearing? The huge looking inner race looks very heavy. I'd much rather have larger ball bearings and thinner races. But I take it that such dimensions are not standard. 37x22x7. 6805 bearings are readily available and are 37x25x7. We have had a good experience with NTN bearings.

I've also never installed a gxp crank before. Are there any pointers for someone that has only installed fsa bb30 (wavy washer) and shimano cranks? I've seen a star shaped dust cap in some pictures. What's the deal with that?

Thanks for reading and for commenting.

/a

[jlok]

AFAIK the NDS bearing doesn't have the plastic sleeve like the DS bearing does.

The NDS side axle dia is 22mm so that when tightened the axle and the crank will sandwich the NDS bearing inner race (yep that funky protruding part). That way the whole crank is fixed with reference to the NDS bearing. The wavy washer on the DS is just to push lightly on the dust cover and is not meant to preload the DS bearing.

The best way to reduce weight is to use an adaptor sleeve to convert the ID of the NDS bearing from 24 to 22mm (1 or 2g at best). But the best way to avoid issues like noises is to not to use adaptor imho.

The smoothest native (no adaptor) GxP BB90 NDS bearing I have used so far is the Enduro Zero. I think you can get it in wheelsmfg.com.

[743power]

Echo above comment, wheelsmfg or endurobearingsonline both sell individual left gxp bearings, for instance: MR 22378 LLB-E basic deep groove steel bearing. You may be able to look up 22 id 37od 8 w from other manufacturers if you are not in the states.

[alcatraz]

Thank you very much. I had no idea gxp worked this way by sandwiching one bearing race.

Immediately I have a follow up question and that is if anyone has had any luck at all using these shimano-to-gxp adapter insers. Wont they screw up this sandwiching by allowing the crank to float with whatever side play the insert has?

How tight will the sandwiching be? I'm afraid there is no chance of success if I have plastic inserts that will immediately crack to pieces when tightening the left crank bolt. The ones we have are pictured to the right in the picture below.

/a

[jlok]

Somewhere ard 50Nm to tighten the NDS arm. Never seen GxP plastic adaptor / reducer. Good luck.

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[Marin]

I'm running Shimano BBs with GXP cranks on several bikes for weight and reliability reasons.

I'm using the J&L adapter machined down to the exact width (13mm?) of the left GXP left bearing, expoxied in place so the outer position matches the GXP bearing. No issues in several years.

[alcatraz]

Somewhere ard 50Nm to tighten the NDS arm. Never seen GxP plastic adaptor / reducer. Good luck.

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They are not gxp reducers. They belong to the shimano bottom bracket. The bearings are japanese industrial standard 6805 bearings that are 1mm narrower and 1mm larger inner diameter. So the plastic insert makes them shimano compatible. It's all a high quality bb90 shimano bb that was supplied by an authorized trek store.

I just found out that these gxp inserts can be found in both 24 and 25mm outer diameter to fit both types of bearings. The shimano non-industrial and the industrial 6805. Sweet.

Just gotta make sure I get all the necessary parts: wavy washer and gxp dust cap for the left hand side.

/a

[jlok]

yes it happens on the DS bearing as it's the same for GxP and Shimano cranks. but i haven't seen anything like this for GxP NDS bearing.

anyway good luck with that.

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[wheelbuilder]

The easiest thing to do is get the Chris King conversion kit number 7. It has a perfectly machined sleeve to fit over the reduced end of the spindle, turning the spindle into 24mm on the non drive side. It's supposed to be used with CK bearings, but it doesn't matter. Your spindle is now 24mm.

[Marin]

Problem is GXP cranks have no way to set preload, you just tighten them down fully against the left bearing.

[alcatraz]

If the play is noticeable then maybe just beef up the DS wavy washer a little to give it a bit of preload. Maybe adjust your fd as well.

I guess it depends on the quality/condition of your bearings. The play can only increase with time.

Thank you all for clearing up the matter. I think I can do it now.

If not we'll get one of these little surprises.

[jlok]

GxP DS doesn't need bearing preload I think, unless you are using angular contact bearings.

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[alcatraz]

Problem is if you have a few tenths of a mm play in the NDS bearing your shifting might be a little off. A little preload can't be bad.

/a