Left crank problem

drewfromrisca

The left crank i constantly coming loose. They are FSA slk's approx 3 years old. Does this mean the whole chainset is kaputed? Ive heard that if it keeps coming loose then there is no stopping it?

Jamey

Is this a square taper set-up?

Crank bolts need to be extremely tight. Almost ridiculously tight, to the point where you think you might round out the bolt head. I use a torque wrench and do mine up to 75 Newtons and even then they usually need a top-up after the first ride or two, especially if the cranks are new.

You won't be able to achieve 75 Newtons with a hex key either so don't even try. And if you're using a multitool then forget it. 75 Newtons would cause a multitool to shatter. You need a specialist tool like the Park CCW-5 or a big torque wrench (or normal wrench) with a sturdy 8mm hex bit. Even a small wrench with an adapter to take larger bits will not do the job (I know, I've sheared an adapter trying).

Also do not grease the axle or the cranks, assuming they're aluminium and the axle is steel. If you grease them everything gets even worse.

The thing to check is the corners of the square hole in the crank itself. If you've damaged the crank (by riding the bike with the crank bolt too loose) then there's a decent chance you might have rounded the corners. If that's the case then you'll probably need a new crank as it's very difficult to get it to stay put after the corners are gone, so I'm told.

Be aware that the hole isn't meant to have perfectly sharp, square corners, though. They design them with a little bit of a 45-degree angle across them but it's just that (angular) rather than being properly round. Difficult to describe in words but take a look at the same square hole on your right crank (assuming that's ok) to see what I mean.

Left cranks are more susceptible to these problems than right cranks because the right crank drives the chain directly and the axle really just holds it in place, whereas the left side can only create driving force through the axle and so has a lot more strain applied through the interface with the bottom bracket.

HTH.

drewfromrisca

Cheers Jamey I'll check those things out further.

John.T

Your cranks are probably the Mega-exo fitting. Go here http://road.fullspeedahead.com/fly.aspx?layout=tech&taxid=74 . Download the instuctions for the SLK cranks. If these are like yours they have a habit of coming loose. Fit them as per instructions using loctite on the splines. If they still come loose then I am afraid the crank is U/S.

drewfromrisca

Today I gave them a really good tighten. They seem to be ok actually. Fingers crossed it's ok. Thanks for all the help fella's.