My first post on here but not my last.
I was hoping someone could help me with a crank arm problem. My left oval 520 crank arm came right off my bike last night and although I have worked out how to put it back ( with an 8mm +16mm hex) there seems to be something missing as the arm is rubbing on the bottom bracket . Does anybody know if there should be a washer or spacer in the assembly ?
Many thanks in advance.

First I'm unsure what your "oval" reference means. Is this a name? (And if so then a capital first letter would help indicate this).


Taper square crank arms rely on their fit onto the spindle taper to have 100% of interface contact, the arm's hole's walls/faces must be flat so to contact the steel spindle's flat taper faces. The typical failure is when the arm is allowed to become loose on the spindle (as in a lack of proper retaining bolt tightening) and the steel spindle wallows out the arm's square taper. (I explain this to customers as being like when you stick a snow shovel into the snow bank the shovel is very well held. But when you wiggle the shovel back and forth the snow gets pushed away from the shovel's blade and now the shovel is loose and likely to fall over). I suspect your arm's tapered hole is now quite distorted and the arm will no longer fit snugly and likely, with the also enlarged hole, fit further up the spindle's taper. I suspect this arm will no longer stay put with any amount of retaining bolt tightening and will fall off in short order.


The arm likely needs replacement, a minor cost of $15-$20 at most shops. Don't expect an exact copy will be available as the source that Trek uses to get crank sets is different from the source that the shop does. But the same tapered hole (and it's rotational configuration), arm length and any slight curve/offset (as in straight, low profile or super low profile) the arm has should be available. Hopefully in a color that's close too.


For the future- the retaining bolt needs to be initially tightened to about 30 foot lbs of torque. I strongly suggest that after the first few rides this torque is revisited to insure any bedding in (remember the arm is a "soft" AL and will slightly mold it's self to the harder steel spindle) is compensated for. And check the drive side retaining bolt while you're at it.


BTW if your LBS isn't willing to explain all this when you buy the arm from them you need to vote with your $ at another shop that does value a smart customer. Andy.

By oval do you mean biopace? On an old Trek 520 maybe?

Thanks for the replies so far- by oval I mean the model of crankset - Oval Concept 520 made by ovalconcepts from Germany . The bike is a Fuji Sportif

Unusual. I have no answer.

Oval Concepts was an independent company when first started, but the parent company of Fuji, based in Philadelphia, bought the brand in 2010, and Oval has been the "house brand" of Fuji since then. Some Oval Concepts parts can still be purchased separately also.

The Oval 520 (and 720) borrows (licenses?) the SRAM GXP design. There is a bearing shield that fits over the splined end of the spindle between the BB and the left crank arm.

Thanks you for the info - super
I don't suppose anyone has a picture or a plan of what the spline looks like ?

Here's a photo of the bearing shield:

shield.jpg

I have no idea if SRAM sells replacements for these or if you have to buy a complete GXP BB. Also note that some Oval cranksets come with BBs made by Praxis. They're GXP compatible, but I don't know how closely their design matches SRAM's (in other words, a SRAM bearing shield may or may not fit a Praxis GXP BB).

Super and very many thanks
for your help