Have play in my new Sram Omnium crankset

Discuss light weight issues concerning road bikes & parts.
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fozworth
Posts: 9
Joined: Mon Aug 04, 2014 2:20 pm

by fozworth

I've just installed my new sram omnium crankset onto my Cinelli mash work frame.Its a Std 68mm BB. I've greased all parts as per normal setup. Once I've tightened the non drive side with the Allen key (not with a tourque wrench as I don't have one ) there still seems to be some lateral play .Ive remove the crank arm and retightened it but there still seems to be the same play. I know I need a torque wrench and will borrow one but I've done up the bolt pretty tight .Am i missing something ? There were no spacers in the crankset kit so I assume I don't need any either ?
Cheers Ja

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Juanmoretime
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Posts: 7063
Joined: Sat Jun 19, 2004 11:08 am
Location: Urbana, Illinois

by Juanmoretime

I've not installed an Omniun but all other SRAM cranks I've installed had a wavy washer.
RESIDENT GRUMPY OLD MAN.

11.4
Posts: 1106
Joined: Tue May 23, 2006 4:33 am

by 11.4

1. Wavy washer.
2. The stock bottom bracket that usually comes with the Omnium is pretty crappy. I've found bad tolerances, missing parts, you name it.
3. Is the play in the bottom bracket or in the crank (since you mention being concerned about torquing the cranks)? The Omnium chainring is thicker than standard track chainrings, so if you substituted a ring and used the same chainring bolts, your chainring can sometimes be a little loose on the crank arm spider.
4. I've found the splines not to be consistent in dimension on the bottom bracket. Try refitting it. There's a torque spec, but the crank doesn't have to get forced onto the crankset too hard -- like with Shimano's Octalink, it simply goes on until it stops.

fozworth
Posts: 9
Joined: Mon Aug 04, 2014 2:20 pm

by fozworth

Hi ,I've got no waves washer but on the sram omnium exploded drawing there isn't one ? I'm using the sram chain ring and the play is up and down but also I can move the crank axle left to right about 1mm .I need to get a torque wrench on it to see if I'm tight enough I guess before panicking as this might eliminate all probs if I'm not up to correct torque .

11.4
Posts: 1106
Joined: Tue May 23, 2006 4:33 am

by 11.4

If the axle is moving then you've isolated the problem to the bottom bracket installation itself. That needs to be done right, and you might need to have the bottom bracket faced properly and then have a shop professionally install the bottom bracket.

fozworth
Posts: 9
Joined: Mon Aug 04, 2014 2:20 pm

by fozworth

It's a steel frame and faces look good .Ive installed heaps of external Bob's and never had any issues till now but it might be down to the torque

mattr
Posts: 3507
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

There is no "bottom bracket" to install by the sounds of it, just the two external cups (68mm bottom bracket).

If the shell is *actually* 68mm (measure it, i've had under and over size ones) the only adjustment is pulling the crank onto the spline, and it's a lot of torque, if you are only using a standard L shaped allen key, you're unlikely to be able to achieve the required torque.

Also, about half the pictures of unfitted/BNIP omnium GXP cranks i can find have a little bag with what looks like a wavey washer in. But a wavey washer might struggle to take up 1mm. You might have two problems.

wingguy
Posts: 3832
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

The generic SRAM crankset manual says wavy washer only for pressfit GXP BBs, not threaded GXP BBs.

In the event of play in the crankset on threaded GXP it says "If there is play in the crankset, remove the crank arms and apply additional grease to the spindle. Repeat the installation procedure until play is eliminated."

Which kinda sounds like a polite way of saying "Keep forcing it until it works" but it's your crank not mine! :lol:

mattr
Posts: 3507
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Probably why I'm seeing bags with wavey washers in them!

fozworth
Posts: 9
Joined: Mon Aug 04, 2014 2:20 pm

by fozworth

Mmm cheers ,I think I need to tighten things up correctly first and see what play if any I have and go from there.

fozworth
Posts: 9
Joined: Mon Aug 04, 2014 2:20 pm

by fozworth

Got the LBS to torque the crank up and hey-presto no more movment :-)
Thanks guys for the advice n help

Marin
Posts: 2763
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

The Omniums are GXP cranks, so you need Sram GXP external bottom bracket cups. The left cup has a 22mm internal diameter, the right one 24mm (Shimano e.g. have 24mm bores on both sides).

GXP cranks clamp the left bearing between the 1mm step in the GXP axle and the left crank arm - this is why you just tighten the bolt and don't have to adjust play.

The axle is not fixed to the right bearing, it just floats there, and all side forces are carried by the left bearing. This is why the left bearing will often wear out 1st.

grover
Posts: 1123
Joined: Mon Jul 26, 2004 1:06 pm

by grover

Marin has it exactly.

On a GXP crankset if there is lateral play you haven't done up the crank bolt tight enough. Once tight enough the non-drive bearing will be captured between the non-drive arm and the 1mm step in the spindle.

On a threaded bottom bracket a wavy washer would achieve nothing.

On a press fit bottom bracket the wavy washer is required to stop the pressfit cup migrating out of the bottom bracket shell.

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