Wobbly Oval Concepts 730 crank arm - Non drive side.

[FluffyChicken]

Re:

So frame is 68mm, but spacers are for 73mm shell, the middle is probably bent as its been crushed.


Now can you see the shiny bit on the axle near to the ring. the Drive Side bearing sits over that.

None drive side sits over the spline to step gap, where it shiny.
place the bearing there and see the problem.

https://wheelsmfg.com/crankset-tech

 

[ishaw]

Re:

As above. If bb is 68mm and spacer for 73mm has been used, it will have crushed the centre tube if the bb and also the bb will not be sitting far enough out, probably causing the extra bit sticking out when you button it all up.

 

[klunkrider]

GXP cranks require you to tighten the nds crank onto the bearing pinching it between the arm and the step in the axle to take the axial load. The nds bearing has an extended shoulder for this reason.

The driveside basically floats axially and is only supported radially by the bearing. This is why GXP bbs wear out faster than Shimano ones that share the radial and axial loads between both sides of the bb.

The crank should nip up onto the bearing before the crank arm bottoms out on the splines or the crank bolt bottoms out on the axle.

Putting the crankset in that bb without an adapter means the axle has not been supported radially (22mm axle in a 24mm hole) and that the nds arm isn't holding onto the bb bearing so it's not been supported axially either.

The crank-axle interface should be pretty tight, requiring the axle bolt to push it on and the self extracting cap to pull it off. If you've been able to slide the arm on to the axle to the point where the axle protrudes (photos 1 & 4 on page 1) by hand then I'd say the splines in the nds crank arm are done for. If it was ridden any distance with that set up then the rest of the components may be damaged too.

 

[Trebz]

I knew there was something fishy about all of this when I saw the crushed centre tube.

So the best course of action would be:

1. Buy a replacement Bottom Bracket of the correct size at 68mm. Fit this and test. If all ok ride the bike and smile.

2. Failing the above class the chain set as a write off and replace this also. Fit this and test. If all ok ride the bike without a smile.

Ok?

Thanks for the input by the way, i was lost with this one.

 

[Trebz]

Re:

This maybe:

https://www.ebay.co.uk/itm/Shimano-Deor ... Swc0FUquRP

Or this:

https://www.ebay.co.uk/itm/Shimano-Tiag ... SwhcJWNKY8

 

[klunkrider]

No those are both Shimano bottom brackets.

To use those Oval Concepts cranks you need a GXP bb like this - https://www.merlincycles.com/sram-gxp-b ... source=PHG

Though since I suspect your nds crank is buggered and with GXP being an inferior system due to taking all the axial load on one side then I'd actually recommend getting a Shimano HT2 crankset, 2 additional bb spacers and setting the bike up correctly with Shimano kit.

 

[FluffyChicken]

Re:

Sack it all and get a new BB/chainset, they often come together.

keep the current BB cups for when it is needed for something else.

 

[Trebz]

Update: We were all wrong.

I popped to the Local Bike Shop (modern heathens), something iv'e not done since the eighties, they took one look at it and said 'Spacers mate'. He grabbed a pack of bottom bracket spacers and gave me them for free, there's about five in a pack of varying thicknesses. I popped back home, put an additional spacer on the non drive side between the bottom bracket shell and the frame and hey presto, a working chain set and bottom bracket.

There is an additional issue which I'm researching now in that when I tightened the allen bolt up the chain set / bottom bracket is overly tight and will not spin freely as expected, this is obviously due to the tightening of the allen bolt squashing up the bottom bracket. Maybe I need to try differing thicknesses of spacer to just get it right. Either that or I need the GXP bottom bracket shown above in the post by 'mechanicalvandal'. Clearly someone at some point has fitted the wrong bottom bracket, i guess?

I'll let you know what's happening there when I've finished demolishing this little Pork Pie I have in front of me.

 

[ishaw]

Re:

You still need to have the right number of spacers in the right position. If you are crushing the bearing you have too many spacers.

Heres a link with details for both shimano and gxp.

https://off.road.cc/how-many-spacers-in ... h-sram-gxp

Spacers should be 2.5mm width. If your pack contains different widths, you need to make sure the total widths add up.

For your 68mm bb using a shimano ht2 bb, you need 2 on drive side, 1 on non drive side.

Evidence suggests that the oval concepts cranks are gxp, so maybe the shimano bb has the adapter in it? You can confirm by measuring the axle width at each end. If it is 24mm one end and 22mm the other, its gxp, if 24mm at both ends its not gxp and you don't need the adapter for the bb.

 

[ishaw]

Re:

I'm still convinced you have a gxp axle as there is a step down from the axle to the spline and the bearing sits on the 22mm section, not on the 24mm.

Here is another link.

https://wheelsmfg.com/crankset-tech

You'll be barking up the wrong tree using the shimano bb if it hasn't got the adapter to cope with the 2mm smaller diameter axle on one side. If you were using a gxp bb, spacer numbers are also different as the bb cups are wider (13mm vs 10mm if my research is correct).

Up to you if you want to plough on with spacers but I think your lbs is wrong and you need a gxp bb unless your ht2 one has an adapter like this:

https://www.ebay.co.uk/itm/232700248541

Then you need to work out what spacers you need.