PSA: Crank arms with a diamond top fitting come in two different alignments (read thread)

[EpicFishFingers]

Okay so my crank was stripped and wobbling even when fully tightened. I have this kind of bottom bracket on my bike and the cranks are 175mm long. Not wanting to pay for the replaement as I know what I'm doing, I went to the LBS and bought a crank, £9.99 down.

Problem is when I put in the pedal and tried to put it back on the bike, the crank arms weren't parallel. Google yielded nothing except something about "cottered cranks" (my ranks are not cottered, or bent, stripped, etc.)

I just figrued out the problem, see this comparison image I took of how they fit onto the bottom bracket.

The new crank is on the left, the stripped one is on the right. Notice how the stripped one has a diamond-angled fitting and the replacement crank I bougth has a square fitting. BOLLOCKS

The LBS is now shut too, gonna have to try a different shop. There go my pla ns of going on a quick ride...

So just so tyou know, there are two different styles: diamond and square. Also measure your cranks from the centre of the pedal to the centre of the hole for the length, which is important! Thelength in mm may also be engraved on the back of the crank

 

[andrew_s]

I was caught like that once
You can't even guarantee that the same brand uses the same orientation on all its cranks.

 

[lpretro1]

I have a box of spare used crank arms - with the different shapes if its any help

 

[User6179]

Spent a hour or so taking crank arm off old bike to replace the one i had snapped only to find the result was cranks at 10 to 2 lol

 

[Sterba]

You could have inadvertantly discovered a whole new way to apply power to the wheels. This slightly offset pedalling style could be patented in the same way as biopace ovalised chainrings. Cav would adopt them for the sprint up the Champs Elysees and soon after your invention would go viral and Trek would offer you huge royalties. Thus is technological advance made. Eureka.

 

[RecordAceFromNew]

Not just the diamonds can be differently orientated. You would be lucky if they have the same q factor, or designed for the same square taper and spindle length etc.