rstarr

Just starting to work on my own bike, so I have a basic question.

I just bought a Marin Belvedere. The left crank arm was off when I bought it. It has Truvativ IsoFlow cranks (square tapered spindle). From the reading I have done, I understand that these are bad cranks, and should just be replaced (probably replacing the bottom bracket with something besides square tapered).

But for now I just want to get the left crank back on. The bolt for that crank is missing. How do I determine what size/type crank bolt I need?

Thanks for any help.

ultraman6970

I believe its a M14?? cant remmeber, look at ebay, is full of those bolts man. The other thing is that like 95% of the time those bolts are metric so it is not something you will find in home depot.

Advice, go to your lbs the guy might have zillions moving around for sure or call the guys from bike tools etc, they for sure have one.

This is what you are looking for...

https://www.biketoolsetc.com/index.cg...em_id=FS-ACB14

cheers

FastJake

If the bike was ridden around with the crank bolt missing there's a good chance the arm has gone loose. When this happens the square taper or splines get enlarged and this almost always ruins the arm.

Fortunately, left arms are cheap and plentiful if you do need to replace one. There's really no reason to ditch square taper unless you buy a different crankset that uses a different system.

desertdork

Do you know why the crank arm was off the bike? If the arm fell off during riding as the result of improper installation, it may have worn to the point that it no longer is a "press-fit" match to the square taper spindle.

If you have never installed a square taper crankset, you might want to take a few minutes to read up on it before proceeding. It's not that difficult to do correctly, but it's not difficult to do incorrectly, either.

Edit: I'm a slow typin' and a slow a thinkin' tonight, FastJake

Nerull

A hardware store with no metric bolts is a pretty crappy hardware store. Further that bolt is for ISIS cranks, not square taper. You would want something more like this: https://www.amazon.com/Truvativ-Caple...ef=pd_sbs_sg_2

rstarr

Thanks for the help.

The left crank on this particular crankset is apparently notorious for falling off, so I believe it fell off from regular riding.

I have read a bit on square taper crank installation and think I can handle it. The crank seems a bit worn/rounded on the back side of the connection with the spindle, but the leading edge looks to be still square and it fits snug against the spindle. If the crank is indeed out of square, then it won't do any new damage to ride with it like that, right? Will probably just loosen/fall off more, but not damage the BB/spindle, correct?

Also, how far is the crank supposed to go onto the spindle when first putting it on by hand? Just far enough to get the bolt started? I should expect the tightening of the bolt to pull the crank arm a fairly good distance onto the spindle, correct? Sorry, I just have not seen a good picture/video of the crank arm on the spindle before tightening.

Finally, to the original question of bolt size. How are you determining what size bolt I need? Do all square taper bottom brackets generally take the same size bolt? All Truvativ square taper bottom brackets? Is there a place to look this up? I want to learn how to find this information on my own but don't know how to start. And the threading that is on the actual crank arm, that is only for the crank puller, right? The crank bolt does not thread into this in addition to threading into the spindle?

Again, thanks for all the info. Knowledgeable helpful folks make this fun to start figuring out.

desertdork

Download chapter 20: Press fit crank arms from the middle of this page
https://www.bbinstitute.com/the-barnett-manual

It'll give you some good information.