Got an SLX hollowtech II double and bash crankset and the left hand crank arm came off on a ride today. Had a look inside and the aluminium grooves inside the left crank are shot. However, the splines on the axle look pretty much fine. It’s about 2.5 years old.

Question is, should I replace the left crank arm for £50 or just get a new crankset for £95?

Anyone got any experience of going for the cheaper option? I’d rather not spend £50 to just be back to square one I suppose but cash is tight at the mo…

Advice appreciated…

J.E.James – LX chainset £50 or Merlin Cycles – SLX chainset for £75 & sell the rings

If cash is tight you could go down the budget route and get a spare deore crankarm for less than £25. Won’t look pretty though.

But you’re gonna need new chain rings at somepoint so a full chainset would probably prove to be cheaper option long term.

Buy the crankset and you will solve the problem and have spare rings to replace later and a BB. Spend 50 quid and the BB will fail next week and you will find one of your rings are too worn…

Buy the crankset. Keep the rings and BB as spares. Sell the drive side crank to someone that stripped pedal threads or something.

Probably wouldn’t mix and match old and new cranks, it may look fine but they also may be worn which could make it misbehave or trash the new arms.

Will you swap the rings over from old to new if getting the chainset, or will you need to factor in a new chain and cassette?

Put the old rings on a new Deore or SLX crankset (the new Deore looks pretty good and is a bargain). Either keep the drive side as a spare or stick it on ebay (what I would do as there is bound to be someone who wants one).

then when the drivetrain is shot dig out your nice new rings.

Yes, I’ve had exactly the same happen a few years ago, crank arm came off whilst I was hacking up a steep hill out of the saddle, knackered the splines , the axle tube splines will be fine tho especially if they look it(as you say) it’s a harder metal. I bought a new crank arms and it has been fine ever since.

Some interesting replies, thanks to all.

Was set on buying a new crankset until BANana got involved!

Hmmmm……

How long have had the replacement crank arm on for now BANana?

I bought an XT replacement NDS arm yonks ago, can’t remember price but must have been fairly cheap, still running fine.

Check the replacement crank arm is for an M665 not an M660. They look the same, but the M665 has steel pedal thread inserts, which are well worth having if you bash the pedals on rocks a lot like I do!

Thanks perthmtb. I do and I will.

go down to your LBS or even local chain and ask them nicely if they have any left hand cranks in the spares bin.

They will quite often have these as leftovers from where people have replaced cranksets on off the shelf bikes or where they have simply lost the other part.

They will usually give you a good price too.