Crankset/BB question... isis / powerspline... same thing or not?

[MontyVeda]

Actually a few questions...

I'm seeing cranksets advertised as 'isis/powerspline', but i seem to recall they're not the same... contrary to what some specs state and leaving me wondering if i can trust them. Can anyone shed any light please?

My current cranks are Truvative Fire-X with ISIS Drive stamped on the side. I replaced the bottom bracket about a year ago but in recent months I've noticed that the cranks are a tad loose whilst the bolts are still as tight as the last time i tightened them (b@stard tight!)... so i'm guessing the splines might be worn (the crankset is a good 12-14 years old, but the rings have been replaced a couple of times). Do the splines wear over time?

I'm not entirely sure if this issue has developed since i fitted the new BB, or if it's just taken me a while to notice... so it could be that my newish inexpensive BB is a slight mis-match. The model number of the BB is MB-603 68x113mm. I seem to recall making sure that i got the correct width, but maybe, in a rare 'blonde' moment, i did buy the wrong one and should have got 68x118mm or 68x108mm (or???). Would the wrong width cause the cranks to be slightly loose even when proper tight on the BB? (I assume it'd just put the cranks closer together or further apart rather than affect the 'seating'.)

Clearly, I'm baffled.

 

[lpretro1]

Shimano Octalink (8 splines) is not the same as SRAM/Truvativ powerspline or ISIS (10 splines) so cannot be interchanged. Having the wrong length axle wouldn't cause them to be loose but it would mean if too long cranks are too far out for fd or too far in and might catch the frame

 

[MontyVeda]

the cranks certainly ain't catching the shell, there's a good clearance so the axle width can't be too short... but I'd guess the spline depths would be the same regardless of axle width??

and just to clarify, are ISIS and Powerspline interchangeable?

 

[lpretro1]

ISIS/Powerspline all the same thing. With the splined bbs there shouldn't be much of a gap bewteen cranks & bb once tightened right up. You just need to get the right length axle to keep a good chainline. If you remove the cranks then measure the axle width with some calipers then buy the correct length

 

[MontyVeda]

ISIS/Powerspline all the same thing. With the splined bbs there shouldn't be much of a gap bewteen cranks & bb once tightened right up. You just need to get the right length axle to keep a good chainline. If you remove the cranks then measure the axle width with some calipers then buy the correct length

Thanks for that... I'm 99% certain the lenth is good, the crank bolts are tight, yet the cranks still wobble a tad on the BB... so it must be the splines that are worn on the crank side of the interface. They are over a decade old after all.

 

[lpretro1]

If it is a new(ish) bb the it sounds as though the wear is in the crank arm itself if everything is tightened up as you say. Cranks are usually made of much softer material; than bb so if there is still play then crank needs replacing

 

[MontyVeda]

Well now I've finally got round to putting the new cranks on... it's clear that Powerspline and ISIS are not the same thing

Powerspline on the left, is clearly a much smaller interface than the ISIS on the right.

 

[Hacienda71]

Send it back or get a compatible BB are your two options.