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I need to move my LH crank (Ultegra 6800 Hollowtech 2) outboard on the BB axle by adding a spacer between the crank and the push fit bearing.
Long story short is the strain gauge / battery case of the power meter is fouling the rear brake, which, in Trek's wisdom - is on the chain stay not the seat stay.
I have access to a machine shop so can have a spacer made accurately / easily. Question is - will I die. I want to move the crank out 5mm, which will reduce the interface on the splines obviously. I will be 'splitting the difference' and grinding down my brake pads so I can wind the caliper in a bit - this will gain some clearance but not enough to negate needing a shim/spacer.
if it helps swing it this modification will only be needed for about 6wks before I get a new bike. I probably dont need to do too many out the saddle efforts in those 6wks
I think the crank arm will walk off the splines. Do you have a lh arm without a power meter or if it does not work can you remove it? What about using a different caliper?
The chain stay is the normal position for brake mounts on road bikes
Im always up for a bit of impromptu modification, but for the sake of 6 weeks isn't it easier just to remove the power meter?
im also assuming you're talking rim brake caliper, unless your crank arms are 600mm long
5mm on the crank interface seems a lot and a recipe for mashed up splines to me as the crank walks off the spindle.
As above - just do without the meter for 6 weeks.
I’m with @nixie on this, i think the crank arm will just work loose.
quite quickly.
having a crank fall off during a ride could range from mildly annoying to reasonably serious leg injuries.
for 6 weeks I would just remove the power meter.
It depends on how much axle is still in the crank. Can you loosen the crank and move it 5mm out to see? I did this with an MTB crank on my road bike and it eventually broke
I assumed a cable disc 😂. Rim caliper makes lots more sense. Road rim.calipers fit to a single hole don't they? Any scope to run it on the other side of the hole? Would that mean it sticks out less. Best option would be just to run minus PM. Any lh ht2 road crank of the same arm length should do it.
You could apply some loctite to the splines which might help. Or might just delay the inevitable.
Is a slimmer profile brake a possibility?
I messed up the spaces installing cranks once. no idea how I didn't twig, too many shed beers maybe. I did tighten up the pinch bolts properly, having just bought a torque wrench.
Crank was 5mm too far off the spindle.
It worked loose on a ride, I had to buy a new crank.
I think it took a while though, you *might* be OK for 6 weeks, especially if you're using the power meter to make sure you keep your power under 100W!
I wouldn't, though.
I assume the problem item looks a bit like this:
Picture of someone's bike upsidedown.
In which case would some sort of direct mount centre-pull/aero brake allow you to keep the cranks as they are?
As described above, adding an extra spacer is likely to lead to a worn spindle and failure.
Do you have a spacer on the driveside that you can swap to the NDS? Not ideal for chain-line (and you will need to check clearance) but will keep the over all width the same.
No but you might lose some teeth, do you enjoy having teeth?
Blimey!) I didn't know that lunacy was a thing on road bikes, only remember U-brakes and rollee-cams from the late 80's with that daftness. At least the excuse for locating them down there in those cases was that the seatstays would have deformed due to the leverage of those brakes.
For 6 weeks I'd rather run no rear brake than bodge the crank spacing. I'd say that there was a fairly high chance of destroying the cranks - having had Hollowtech cranks come loose before, it doesn't take much to destroy the splines. Front brake only really isn't that bad.
Don't do it for all the reasons above. Buy any shimano HT2 LH road crank and go powerless for a bit.
any scope in the BB spacers to be rearranged to push the whole crankset across, and the fun of messing up the chain line, setting up front and rear derailers etc?
24 hours late
Thanks for the replies.
It it is a trek with a rim brake on the chain stay (not seat stay) as pictured. I could investigate winding the caliper brake in to give more clearance but don’t think it will be enough.
I’ll give it a pass then: I have a gravel bike that I can use.
Or investigate removing the power meter.
I would like to sell it when new bike arrives so want to keep it in sellable condition (the power meter chainset that is)
If there isn't a BB spacer you can shift across from the driveside, it sounds like you might have a 4iiii Precision 2 left crank that might be expensively/safely solved by a Precision 3.