Replacement left hand crank

[nick_a_louse]

Hi all,

I took the quiet roads as a good excuse to start cycling again (after a year long hiatus). Did a quick service and everything seemed alright, but after about 20 minutes on the road, my left crank started coming loose. Unfortunately I didn't have any tools, so it was a slow trip back with a wobbly crank (hand tightening every so often).

In my naivete, I thought it was just a case of tightening up the allen bolt and away we go. Sadly, it started to wobble after another half an hour and having taken it off, I can see that the corners are now slightly deformed and it needs replacement (the shaft of the bottom bracket looks ok).

So, I need a new crank, but there doesn't seem to be a reasonably priced replacement around. Specs are:

- 175mm length (centre of hole to centre of hole)
- Black
- Diamond hole
- Alloy
- Off a Specialised Sirus

Anyone able to suggest a replacement part that is actually in stock, or am I going to have to get a full crankset?

 

[Sharky]

Make sure you haven't left any debris in the crank. I did once and the crank kept coming loose. Once cleaned, the crank bolts tightened up properly.

For a lh crank try sjs cycles

 

[faster]

If it's not too damaged, I've had luck before by giving everything a really good clean, applying red loctite to the taper and threads then doing it up nice and tight.

Obviously, not so much you snap the bolt! Once set, don't re-tighten or it'll break the bond of the thread lock.

 

[nick_a_louse]

Thanks, I'll have a look when it's stopped raining, but I suspect the damage is done (a couple of flakes were in the grease that got on my hand).

Had a look at SJS, but no left hand 175mm cranks on their own (so hopefully someone else can throw a suggestion my way)

 

[IaninSheffield]

Had a look at SJS, but no left hand 175mm cranks on their own (so hopefully someone else can throw a suggestion my way)

Are you sure? https://www.sjscycles.co.uk/cranks-left/?length=175&order=price+ascending

Or something less premium, try Halfords https://www.sjscycles.co.uk/cranks-left/?length=175&order=price+ascending

 

[rivers]

Make sure you use a torque wrench to tighten it to the correct specs as well. And don't lose the little piece of plastic that sits in between the bolts.

 

[nick_a_louse]

Are you sure? https://www.sjscycles.co.uk/cranks-left/?length=175&order=price+ascending

Or something less premium, try Halfords https://www.sjscycles.co.uk/cranks-left/?length=175&order=price+ascending

Potentially stupid question, but are the Shimano Alivio octalink connections to accommodate both square and diamond fittings, or it's a proprietary fitting? I assumed they were for some sort of spline (as the descriptions never explain this). Otherwise, the only diamond fitting I can find on the SJS page is silver (which would look a bit weird since everything else is black). Can't see any 175mm diamond fitting cranks on Halfords.

Unless I'm missing something....

 

[nick_a_louse]

Make sure you use a torque wrench to tighten it to the correct specs as well. And don't lose the little piece of plastic that sits in between the bolts.

Haven't found an online manual for my bike yet. Is there an approximate recommended value?

Edit: I think it's supposed to be 34.5Nm

 

[Rickshaw Phil]

Potentially stupid question, but are the Shimano Alivio octalink connections to accommodate both square and diamond fittings, or it's a proprietary fitting? I assumed they were for some sort of spline (as the descriptions never explain this). Otherwise, the only diamond fitting I can find on the SJS page is silver (which would look a bit weird since everything else is black). Can't see any 175mm diamond fitting cranks on Halfords.

Unless I'm missing something....

No I don't think you are missing something. Octalink is a splined fitting so not compatible with what you have.

I did think of Spa cycles, who do have black left-hand cranks with the right hole orientation but only in 165 or 170mm.

You may end up having to buy a complete chainset. This one at £20 is no more expensive than some of the arms on their own, has the right orientation of hole and the right arm length: https://www.decathlon.co.uk/bike-triplebottombracket-789-id_968556.html

 

[rivers]

Haven't found an online manual for my bike yet. Is there an approximate recommended value?

Edit: I think it's supposed to be 34.5Nm

Mu crank arm says it on the arm. Mine is between 12-14 nM. What crank is it?

 

[IaninSheffield]

Potentially stupid question, but are the Shimano Alivio octalink connections to accommodate both square and diamond fittings, or it's a proprietary fitting? I assumed they were for some sort of spline (as the descriptions never explain this). Otherwise, the only diamond fitting I can find on the SJS page is silver (which would look a bit weird since everything else is black). Can't see any 175mm diamond fitting cranks on Halfords.

Unless I'm missing something....

My fault, sorry. Defer to @Rickshaw Phil

 

[Cycleops]

I’m a bit confused, by ‘diamond hole’ i assume you mean square taper, in which case the chainset linked by Rickshaw Phil would be a good choice. Don’t be tempted to buy a Octalink chainset.

 

[Rickshaw Phil]

I’m a bit confused, by ‘diamond hole’ i assume you mean square taper, in which case the chainset linked by Rickshaw Phil would be a good choice. Don’t be tempted to buy a Octalink chainset.

Square taper comes in two orientations. Square like this Thorn crank: https://www.sjscycles.co.uk/cranks/150-thorn-left-hand-crank-arm-black/ and diamond like the one I linked to: https://www.decathlon.co.uk/bike-triplebottombracket-789-id_968556.html

Get the wrong one and you get cranks at funny angles.

 

[Ajax Bay]

- Off a Specialised Sirus

Chain set	Stout, forged alloy, 48/38/28T w/chainguard

Probably worth just buying and fitting a new chainset. You want to get out on the road without losing further days.
Maybe this one @ £35 from Spa Cycles? https://www.spacycles.co.uk/m2b0s109p2000/SPA-CYCLES-XD-2-Touring-Triple-Chainset
Not black though.

 

[silva]

I’m a bit confused, by ‘diamond hole’ i assume you mean square taper, in which case the chainset linked by Rickshaw Phil would be a good choice. Don’t be tempted to buy a Octalink chainset.

Reasons for the latter are?