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How tight should a crank fit onto bearing surfaces

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How tight should a crank fit onto bearing surfaces

Old 08-11-23, 10:48 AM
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How tight should a crank fit onto bearing surfaces

Hi,

I have a FSA omega crank that fits through bearing shells. The crank has virtually no interference binding onto the bearing surfaces, I was expecting to at least have to tap it out. As I'm experiencing a clunk under load I'm wondering if a worn shaft is the reason.

I'm not familiar with these types of BB so am unsure what is normal!
Any advice appreciated 👍
Regards
Nick
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Old 08-11-23, 12:13 PM
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it may be slipping side to side when ridden.
do the areas where the bearings seat look "burnished"(shinier than surrounding material)? Burnishing indicates movement.

not a fan of FSA cranksets, btw... their CF cranks are known to fail at the Pedal thread inserts regularly., and their entire lineup of any material is also known to make lots of creaking sounds when ridden.

i'm sure someone will be along to say they've never had a problem with theirs, so i'm wrong...
i have an FSA SLK sitting on a shelf right now with bad pedal inserts.. and i removed an aluminum FSA crank from my Linear trail DB after years of dealing with the noises. the noise ended as soon as the Shimano crankset was installed... ahhhhhhhhh...... relief!

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Old 08-11-23, 01:11 PM
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There may be slippage between the spindle and bearing. This MAY cause fretting and worsen over time, plus may wick water causing corrosion. However, it would not typically cause noise.

This is the second thread in short order with the same issue on an FSA bottom bracket, and as the maddog suggests may be caused by axial movement. Be sure that you have spacers in place with the wavy washer (if any) compressed about 1/3 to maintain proper preload and prevent axial slippage.

I'm not a fan of this design, and would consider building up the spindle's bearing seat with a nylon paint or nail polish. BITD my preferred product for similar applications was Liquid Paper, but I don't think it's made any more. There are also Loctite (and other) bearing seating products which wick in then swell to fill gaps and make a proper seat.

Finally, keep in mind that the klunk may not be there, and might, for example, be caused by the BB unit moving in the frame.

Last edited by FBinNY; 08-11-23 at 01:15 PM.
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Old 08-11-23, 01:12 PM
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Hi, thanks for the reply and input👍

The crank looks pitted around where the bearings seat, not burnished and I cannot detect any side to side movement, with or without the washers on the crank. It's a new bike for me, so don't really know the history. I noticed BB noise when I took the bike out for a test ride so knew it might need some TLC!

How tight do the bearings fit on a Shimano shaft?
When I took the non chain wheel crank off, I was surprised that the shaft slid out the other way under gravity with the bike at a very shallow angle. So just seeing if this is 'normal' 🤔
Nick
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Old 08-11-23, 01:43 PM
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IME, Shimano cranks won't move in or out w/o a light tap or two. If you have trouble with an FSA crank and bb take the opportunity to move to Shimano.
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Old 08-11-23, 02:14 PM
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I had an FSA 386 mega exo bb with an Omega crank set. The bb was a piece of crap, the crank set was ok. I replaced both with Shimano products. The crank set is on a bike I gave to my brother, with the proper Shimano bb for it. The only thing, I would definitely not get another of the FSA bb's.
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