Nasty Truvativ Omniums issue

I have a nice frame (68mm BB shell) and some SRAM/Truvativ Omnium cranks & standard GXP BB. On installing the cranks I encounter this problem. The inside of the spider hits the chainstay when you turn the cranks.

Supposedly the omniums give a 41mm chainline, so I added a spacer, making it ~42.5mm. However, the spider still strikes the frame. Only when I add yet another spacer, nudging the cranks to ~44mm, do the cranks turn freely and even then with little clearance. SRAM's manual says you shouldn't need any spacers for a 68mm BB. I've also tried sticking on the wheel, thinking it might bring in the chainstays.

So I'm wondering is the metal on the back of these omniums standing out too much - perhaps they're defective or something.

Anyone out there know anything about this crankset to comment? Are they all built like this, with so much metal hanging out the back? I got this set new, from a seller on ebay.

What is the rear spacing of the frame?

What is the rear spacing of the frame?

120mm

What frameset is it?
Titanium?
Straight chainstays?

From a quick glance it looks like a frame design issue.

hammer time.

You could possibly get a frame builder to hit it with a hammer if you want a skilled pro to do it- I'd probably go that route for peace of mind.

Looks to me like the chainstays are going to be too wide for many cranksets to clear if you want a 41/42mm chainline.

This is of course conjecture based on two low res pictures, so make sure a pinch of salt accompanies the reading of this post.

From a quick glance it looks like a frame design issue.

That was my first impression, but I contacted the manufacturer and they have indicated it might be an issue with the cranks and the built up bits at the back.

I'm happy to accept this for now, as they do seem to bulge a bit and would fit otherwise. I'm curious if any other Omnium users out there have these chunky spider endpoints, and is this atypical of track cranks or what.

The chainstays are straight btw.

What frame is it?

Also I will be stripping my bike down to have it painted soon, so if you are in London you are welcome to stick my cranks on your frame to see if there is an issue with other makes of cranks.

What frame is it - one of those xkcd ones?

Is it a secret?

I'll not be hammering it. I'll post a little more detail when I get home and can measure the 'fat bits' on the spider. Then perhaps I could compare with somebody else?

@Dammit Not living in London btw, but thanks for offering!

OK, I accurately measured the Omnium crank, from the flat of the chainring to the end of the chainring bolt on the spider and got 6mm (see pic below). Is that considered fat or about standard, or what?

Bit of a bummer for you as this is a known issue with those cranks. In their quest for stiffness they have beefed up the spider by a few mm thicker and on frames with thicker stays they strike.

Depending on your frame material you can have the stays pinched or crimped. Best check with a pro on that for advice. Otherwise you need to get another set of cranks and a new BB by the looks of it.

Bit of a bummer for you as this is a known issue with those cranks. In their quest for stiffness they have beefed up the spider by a few mm thicker and on frames with thicker stays they strike.

Cheers Zouo, I didn't realise it had been encountered previously. At least it's not the frame ;) So, thick chainstays and Omnium cranks are a bad idea. Noted!

Luckily I have a fallback plan for the cranks.

I had a very similar issue with my omniums, instructions said no spacers, but i've now got none on the non-drive side and 2 on the drive side. Works a treat, chainline is spot on and no need to smack my 753 tubing with a mallet.

Hope you get it sorted!

Am I right in thinking that with a 135mm rear spacing I should have no problems at all with these cranks?

no, the problem will prob be worse.
because the rear OLD is 135mm, the chainstays will have to come out from the BB cluster at a steeper angle, and give even less clearance.

thats how i see it anyway....

Had a similar problem with an Omega track frame. Solved it by inserting a 115mm BB I seem to remember, which just pushed out the cranks. Chain line was about 42.