Switching from PowerSpline to Square Taper

buddha

Veteran
I've just switched a PowerSpline-BB/Isoflow-Crankset to Square Taper. Not knowing any better I just ordered the same size BB (68x113) as the cranks recommend a 112.5mm BB axle.

However, on installing there is a difference of around 10mm between left/right cranks and the chainstays - around 25/15mm, drive/non-drive side respectively. Also the middle ring is pretty close the the drive side chainstay. I put a 1.5mm washer between the BB and frame to give a better chainline (though this obviously makes the difference between cranks worse).

Should I get a 68x118 or 68x122mm BB, or is there something else I should know?


thanks, buddha
 

RecordAceFromNew

Swinging Member
Location
West London
This might help if you have not read it already.

IME mixing and matching square taper components while trying to get it just right can be very tricky indeed. Instead of using washer, I have applied shims made of metal foil on the taper to fine tune chainline and clearance without ill effect.
 
OP
buddha

buddha

Veteran
Thanks for that. I've got some strips of shim steel somewhere so will give that a try.
Although, in my case I don't really want to move either pedal further out (due to pedal the pedal strike issues I was having). So I may bore a few mm off the outside face of the drive side crank - to move the pedal inwards a little.

I should have just gone down the n+1 route:rolleyes::biggrin:
 

RecordAceFromNew

Swinging Member
Location
West London
buddha said:
Also the middle ring is pretty close the the drive side chainstay.
Hi buddha unless I misunderstood what you meant I wouldn't want to disturb any surface of the drive side crank. Have you considered using narrower pedals or shorter cranks?
 
OP
buddha

buddha

Veteran
RecordAceFromNew said:
Hi buddha unless I misunderstood what you meant I wouldn't want to disturb any surface of the drive side crank. Have you considered using narrower pedals or shorter cranks?
Using shorter cranks is what started this mess;) I switched to 'skinny' 26x1.0 tyres on an 'old' mtb/hack (used to be 1.95 knobblies). Took it for a test ride and had a couple of scary pedal strike issues - in traffic!. So I found a cheap square taper chainset with 152mm (kiddie) cranks on CRC - used to be 170mm Isoflow cranks/Powerspline BB.

The new cranks are very thick (although I get the same q-factor as the old setup). In fact, all the pedals I have tried don't have enough thread to screw in the entire thickness of the crank (there's about 2.5mm extra). I don't see too much of a problem boring a 20mm dia x 2mm deep hole - esp if I use coolant.

Pedal wise, I'm still looking for some cheap flats that are reasonably narrow (this is for a hack). I currently have some old shimano MX30's fitted - now with deep grinding marks from where they hit the road:blush:

thanks BTW:smile:
 

fossyant

Ride It Like You Stole It!
Location
South Manchester
Just checking - you are using a compatible square taper BB and Crankset as there are two types I believe... e.g. Campag/Miche etc use ISO and Shimano and Sugino etc use JIS (Japanese Industry Standard)....

Both slightly different.
 

RecordAceFromNew

Swinging Member
Location
West London
Sorry I did misunderstand what you meant by shaving the outside face of the crank. A 2mm horizontal recess will however likely only make ~1.5mm difference in vertical clearance when leaning over?

Some road pedals like these are quite narrow and with the underside designed to accommodate greater lean. Some form of toe clips are however needed. It is funny how changing one thing can have such knock-on effects on another...
 
Just a thought...
When installing my BB I made the mistake of tightening the drive side all the way in first, which meant that the off side had about 10 mm sticking out when I tightened it and it wouldn't go any further.

I loosened it all off, put the drive side half way, then did the same to the off side and so on. The BB went on properly then, but I had already ordered a shorter BB which was a waste.
 
OP
buddha

buddha

Veteran
Well, I made the 2mm cut out and took it for a proper test ride.

The 152mm cranks really make a difference - NO pedal strike! Even on the slightly uphill 90 corners. Although I think it is still a little too close (I need to stick a camera on the chainstays and see how much clearance I am really getting).

I couldn't setup the front mech without serious cable rub with the granny ring. But realised I won't use that ring anyway - so locked it out.

The fact that the pedals are offset didn't really make much difference either (using flat pedals) IMO. So overall I'm pretty pleased and will probably put up with it until the BB needs replacing.

Thanks for your help everyone:smile:
 
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