Pedal fell off AGAIN!

[Willam]

Does this crank arm fitting look correct? Just fitted a new crank and BB but after one day the arm fell off, now I’m thinking maybe the BB is too big?
The BB is to spec for the crankset HT RS500, the BB size on bike is 68mm, I fitted the road BB with no spacers, have I got the wrong BB for the bike or some other issue? Would I need to use the mtb BB without spacers?

 

[Jenkins]

I take it this is the replacement crankset and is a Shimano unit & Hollowtech II bottom bracket? If you're fitting it to a hybrid or road bike, then I don't think the spacers are needed (except for the wavy washer if there is one). Are you correctly tightening it with the plastic fixing bolt (1) on the non-drive side before putting the little metal plate (4) in the gap at the top of the picture and then tightening the two allen clamp bolts (3)

Apologies if you have already done this, but it's where I went wrong when changing my first Shimano unit and why I now use SRAM as it's just a single bolt fixing.

 

[Willam]

Yeah apparently there are two,different sizes of HT2 the mtb and the road, the mtb is meant to use the spaces as it’s got a short tube? The road you don’t need the spacers, I used the road one so no spacers but from the pic it looks to me that is why the arm keeps falling off, as all the threads are not in contact with the crank arm, if you look inside the Shamino arm, the back half is smooth, with only the front half with the threads, so at most the way I have it fitted there will only be around half of the threads in contact with the axle, I’m thinking it’s either a BB size issue? Or if the pic looks I have it fitted correctly then maybe I just didn’t tighten the bolts enough? Just doesn’t look enough thread for the arm to attach?

The crankset is a HT2 crank and I’ve match it with a Road HT2 BB, the bike is a Whyte Portobello V2

The crankset is a Shamino GRX RX600

Missed your question, yes I used the preload screw, also used the safety pin, I don’t think that has anything to do with the fitting tho, only there to catch/stop the arm if it does come loose?

 

[Cycleops]

Sorry that you’re having this problem. If you have a 68mm shell bb you will need the spacers. On my Specialized steel framed gravel bike with a 68MM shell I have used two on the drive side and one on the opposite. Can’t remember how this was arrived at but I suspect yours will be 68mm too.

I know that there have been problems with this type of spline fixing as Shimano has now discontinued their Octalink system as it could work loose if not correctly torqued and once loose the splines in the soft alloy crank become worn and work loose again even if tightened properly. I hope this hasn’t happened in your case

Good luck.

 

[fossyant]

MTB's are 73mm BB so longer.

Get the instructions out and check. Cranks shouldn't fall off - you'll soon knacker them if not fitting properly.

 

[Willam]

Sorry that you’re having this problem. If you have a 68mm shell bb you will need the spacers. On my Specialized steel framed gravel bike with a 68MM shell I have used two on the drive side and one on the opposite. Can’t remember how this was arrived at but I suspect yours will be 68mm too.

Good luck.

The spacers are for the mtb bikes as they are 73mm, road are 68 so no spacers needed, if I were to add spacers it would make the problem worse as there would be even as for the crank arm to attract to.

I’m at a total loss here but thanks for the reply.

 

[Willam]

MTB's are 73mm BB so longer.

Get the instructions out and check. Cranks shouldn't fall off - you'll soon knacker them if not fitting properly.

Wish it was that simple, there aren’t any instructions, well very basic, Shamino seems to think we all go to the bike shop…yep should have lol

 

[Cycleops]

I also have a Cube mountain bike with this system and that strangely has the same arrangement, 2 + 1.

As per my previous post I hope the crank splines haven’t become damaged.

 

[Cycleops]

Found this on the Bikemagic maintenance site:

3. Conventional bottom brackets come in a bunch of different sizes to accommodate different shell widths, cranks and the use or otherwise of E-type plate-mount front derailleurs. HTII is a whole lot simpler – one size fits all. You get three 2.5mm spacers in the box, which sit behind the bearing cups in different combinations according to shell width and front mech mount. Here we’re using a 68mm shell and a band-on front mech, which needs two spacers on the drive side and one on the non-drive side. If we were using an E-type mech we’d leave out one drive-side spacer and replace it with the mech plate. For 73mm shells you’ll need to leave out the non-drive side spacer and run either one spacer or the mech plate on the drive side.

 

[figbat]

Firstly, it's Shimano.

Next, the threads do not contact the shaft at all. The threads are there for the pre-loading cap to screw into to tighten the crank arm onto the shaft. The connection between the crank arm and the shaft is through the splines so it is these that need to make a good, full contact. The crank arm is than held in place by the pinch bolts, so the crank arm needs to be fully-located so that both of these can pinch on the shaft. The safety tab is also in place, so there are three mechanisms that hold the arm onto the shaft - the preload, the pinch bolts and the safety tab. For all three to fail seems like a serious issue somewhere.

 

[Willam]

Found this on the Bikemagic maintenance site:

3. Conventional bottom brackets come in a bunch of different sizes to accommodate different shell widths, cranks and the use or otherwise of E-type plate-mount front derailleurs. HTII is a whole lot simpler – one size fits all. You get three 2.5mm spacers in the box, which sit behind the bearing cups in different combinations according to shell width and front mech mount. Here we’re using a 68mm shell and a band-on front mech, which needs two spacers on the drive side and one on the non-drive side. If we were using an E-type mech we’d leave out one drive-side spacer and replace it with the mech plate. For 73mm shells you’ll need to leave out the non-drive side spacer and run either one spacer or the mech plate on the drive side.

It’s not made simple, when fitting the HT2 to a mountain bike they assume the bb is 73 so you then need the spaces, the bb will also be marked as mountain, the road bikes are 68mm bb so no spacers needed.

 

[Willam]

Firstly, it's Shimano.

Next, the threads do not contact the shaft at all. The threads are there for the pre-loading cap to screw into to tighten the crank arm onto the shaft. The connection between the crank arm and the shaft is through the splines so it is these that need to make a good, full contact. The crank arm is than held in place by the pinch bolts, so the crank arm needs to be fully-located so that both of these can pinch on the shaft. The safety tab is also in place, so there are three mechanisms that hold the arm onto the shaft - the preload, the pinch bolts and the safety tab. For all three to fail seems like a serious issue somewhere.

Yes I used the term threads incorrectly, I meant splines or spindles. I think my issues is there is t enough spindles showing for the arm to fully attach to?

 

[fossyant]

Don't forget, GRX is a gravel chainset and is for fitting to both 68 and 73mm BB's - it's not a road chainset where the BB spindle will be for road application's only.

Need to double check the instructions as I suspect you need a spacer on the drive side.

Had a similar issue with a Praxis GXP BB - you used a slightly different spacer on the drive side, depending if road or MTB (unlike the SRAM one) - I fitted a 1.5mm spacer on the MTB and the crankset did up too tight - re-checked the instructions, ah 2.5mm needed.

 

[figbat]

Yes I used the term threads incorrectly, I meant splines or spindles. I think my issues is there is t enough spindles showing for the arm to fully attach to?

Well it does look like the splines are not seating fully, if these grease witness marks are to be believed.

 

[Willam]

Don't forget, GRX is a gravel chainset and is for fitting to both 68 and 73mm BB's - it's not a road chainset where the BB spindle will be for road application's only.

Need to double check the instructions as I suspect you need a spacer on the drive side.

Had a similar issue with a Praxis GXP BB - you used a slightly different spacer on the drive side, depending if road or MTB (unlike the SRAM one) - I fitted a 1.5mm spacer on the MTB and the crankset did up too tight - re-checked the instructions, ah 2.5mm needed.

They do say they are compatible with road bike?

Wouldn’t a spacer on the drive side leave even less spindles showing on the non drive side, so even less for the arm to grab onto?