Chris King BB query

[Sergeant Pluck]

I have a Chris King BB. When it was ordered, several years ago, it was listed as a Chris King MTB bottom bracket. It's in a normal 68mm BB shell, currently spaced for a MTB HT2 chainset.

Is there any difference between this BB and the current Threadfit 24? It looks pretty much the same. Perhaps they simply packaged them differently then, selling MTB and road versions differing only in spacers used, whereas now you buy a Threadfit + appropriate FitKit when needed?

To use this BB for a road chainset, do I need any spacers at all?

[BFC]

I run a couple of Chris King BB's on road frames - 68mm shells, no spacers. They are direct replacements for the 7800 Shimano units, using the same fitting tools - some tools engage better than others though.
In use them with 7800 (DA 10sp double) chainsets.

I have not tried the latest CK offerings.

I have experience of various other BB's on my fleet (all 68mm shells):
Phil Wood stainless cup (old), direct replacement for shimano 7800.
Phil Wood aluminium cup (current model) supplied with 3x2.5mm washers this came up narrower than shimano 7800 when directly fitted.
Hope - road version, these come up the same as shimano when the 2x1mm washers are fitted.
Hope 68/73 version, comes with 3x2.5mm spacers, to suit road cranks it will run offset with one 2.5mm spacer.
Shimano R60, same width as 7800 but needs a smaller fitting tool because of reduced diameter.
Shimano 9100, same width as 7800 bits but needs an even smaller fitting tool because of reduced diameter.

As an alternative to spacing the cup(s) from the frame, there are 24mm axle spacers available in a range of thicknesses, but make sure the center tube doesn't get crushed or stop the cups tightening in the frame if doing this.

With the narrower BB cups the hollowtech and Miche Pistard crank arms bottom out on the splines before tightening on the BB, and need spacers somewhere.

Some (fatter) center tubes do not get on with internal Di2 cabling in some frames. Stainless Phil Wood has this problem.

Hope are the ones that don't use a plastic spacer to adapt a 25mm bearing to fit the 24mm axle. Pistard cranks don't get on with old (brittle) plastic spacers.

[Sergeant Pluck]

As an alternative to spacing the cup(s) from the frame, there are 24mm axle spacers available in a range of thicknesses, but make sure the center tube doesn't get crushed or stop the cups tightening in the frame if doing this.

If you had to do one - spindle spacers or cup spacers - which is best? Cup spacers might be more stable as they are fully tightened on to the shell.

The CK fit chart says I need a 1mm spindle spacer on each side, and no cup spacers. But surely the effect is the same?

[BFC]

As an alternative to spacing the cup(s) from the frame, there are 24mm axle spacers available in a range of thicknesses, but make sure the center tube doesn't get crushed or stop the cups tightening in the frame if doing this.

If you had to do one - spindle spacers or cup spacers - which is best? Cup spacers might be more stable as they are fully tightened on to the shell.

The CK fit chart says I need a 1mm spindle spacer on each side, and no cup spacers. But surely the effect is the same?

With 1mm spacers either option is good.
With larger spacers it may be necessary to use cup washers to ensure the correct part of the axle sits fully in the bearing. Comparison of bearing/plastic bush thickness to the length of the 24mm sections of the axle is a god idea.

[Sergeant Pluck]

Thanks. Shall proceed carefully. I’ve just removed said CK bottom bracket and I see the tube says 68/73mm, but that might be specific to the 3 spacer setup needed for a MTB crank. The cup threads are marked MTN.

I suspect I will need another centre tube as well as spacers. Which pushes me somewhat in the direction of just using the Shimano BB that came with the crank.

But I would like to use the Chris King as it would be a waste not to.

Does the 1mm per side advice take account of the fact that these are MTB cups, not the current Threadfits, and are 1mm per side narrower than road cups?

[BFC]

My (ancient) road CK were supplied with 3 thin (o.5mm) white plastic axle spacers, and a label saying they are not normally required.

As far as needing spacers - just make sure the cranks pull up tight before the preload bolt or splines bottom out (put some ultra thin plastic between cranks and BB to check if in doubt), and the drive side (chainrings) has appropriate clearance to the chain stay.

Putting the cups and tube together to measure the minimum usable length between cups will tell if you need a shorter tube/spacers for a 68mm shell.

[Sergeant Pluck]

Bottom bracket serviced, new seals, and refitted, no cup spacers. Centre tube fitted fine once I remembered about moving the O-ring to the more central groove.

I’ve just done a little test fit with the cranks. The cranks fit perfectly with no spindle spacers. Minimal but adequate clearance at the BB, chainstay clearance good. I’m sure it is not bottoming out on the splines but will check again.

In the meantime, I have discovered one of those packs of 3 white spacers you mentioned!

I shall look carefully at it again and decide whether to fit as is or add 1 x 0.5mm spindle spacer each side.

[Sergeant Pluck]

Nope - the cranks are just on the verge of bottoming out on the splines. It needs the 1mm spacer on each side to be sure.

So, for future reference, Chris King BB on 68mm shell, GRX cranks (or any road HT2 I suspect):
- no cup spacers
- 1mm spindle spacer needed on each side