John U

Just wrecked the thread for the crank extractor on my left hand crank - a Sram Truvativ Isoflow

I wanted to replace it temporarily with a left crank from another bike but find the square taper hole is 45 degrees different so the pedals do not line up.

What gives? I thought it would be fairly standard between brands.

ultraman6970

Squared tapper in a isoflow? this things use something called power spline or something like that that is not squared tapper. Unless you are tlaking about something else. If the cranks use that kind;a weird shimano proprietary bb similar to octalink and you are trying to put a squared tapper crank I doubt it will work.

At some point isoflow was matched to a squared tapper BB maybe? who knows.

FBinNY 

It is fairly standard, in that all cranks have holes either corner centered or face centered. You won't fine any other possibilities besides these 2. There's also some variance between JIS and ISO in the width at the center of the taper, which will affect how far up the crank will go.

IthaDan 

Ahh, the old "diamond" vs. "square" dilemma.

Sixty Fiver

Nope... sounds like the aforementioned diamond vs square issue.

If you look at the respective cranks with the pedal down you should see that one looks like a diamond with the point up and the other will be turned 90 degrees and look like a square.

If the extractor threads on the crank arm are wrecked you can still re-install it although getting it off might require a gear puller.

FBinNY 

I prefer not to call them diamond and square, since they're both square, and it's only a matter of orientation. But yes, that's exactly what it is.

Sixty Fiver

Corner centered and face centered are pretty technical terms...

FBinNY 

Maybe, but I figure that anybody holding one of each would figure it out pretty quickly.

The real reason is that I'm a bit too literal sometimes. The only square diamond I ever see is a baseball diamond. If you say "diamond shaped" to me I envision something more like the diamond on playing cards.

Sixty Fiver

But those are also squares...

FBinNY 

I t depends on where you get your playing cards. Mine are rhombus shaped diamonds. (all squares are rhombuses but not all rhombuses are square).

pmt

Yeah, just get a gear puller for future removals.

Rootman

So why not pull the RIGHT crank off the other bike and temporarily switch them BOTH out till you can get a correct match for the ruined one?

FBinNY 

Too easy.

OTOH, there may be offset or chainring issues. I suspect the OPs problem isn't as much that he's stymied, as it's that he's surprised that they're not all the same.

IthaDan 

Alright if square and diamond don't cut it, how about something referential, like "side/flat facing" and "point facing" [the pedal hole] for terminology?

onespeedbiker

Keep an eye open for cranks made by SR Suntour, not the Japanese maker of quality components, but the SR Suntour parts you find on low end bikes; they use the square (vs diamond) orientation with there crank arms..