Left crank coming loose

ijportwine

Hi

I have recently taken up road cycling with a Giant SCR 3, which I am loving. I have noticed, however, that the LH crank bolt can work loose over a short period of time. I have a long handled Allen key to tighten it up; but can anyone suggets a way of preventing the bolt working loose.

Many Thanks

gundersen

tighten it


put a long tube on the end of your allen key and like I said - tighten it

morrisje

I had the same problem. The LBS used a torque spanner on it but still came loose. In the end they recommended a new left hand crank and no more problems.

dennisn

I have had this kind of problem over the years with square taper, isis, and octalink
bottom brackets Not a lot, but yes, on occasion. A few years back I bought a new
Shimano compact outboard bearing bottom bracket. And while some will say that
the pinch bolts on the left crankarm are ugly, I say that they are very functional in
that I have had Zero problems with it. Never has come loose, easy to use, easy to
maintain and change rings on. Gets my vote as one of the top functional designs
to hit cycling in years. I have heard though, more than a few stories about other
outboard b/b such as Campy and FSA coming loose because of the design difference
in the way the cranks are held together. I'm sold on the pinch bolts as compared to
the bolt through design.

Dennis Noward

Monty Dog

I beg to differ - I know of at least two cases of pinch bolts coming undone and rendering the crank useless - it's fugly too! Before ditching the crank, have you tried putting some Loctite on the threads of the bolt or fitting a different bolt?

dennisn

Monty Dog wrote:

I beg to differ - I know of at least two cases of pinch bolts coming undone and rendering the crank useless - it's fugly too! Before ditching the crank, have you tried putting some Loctite on the threads of the bolt or fitting a different bolt?

I'm sure it happens. Nothing is perfect. I guess what I really like about outboard b/b's
is the ease of maintenance on all of them. I know on the Shimano crank you adjust
the bearing pressure with a plastic tool. How does it work with Campy & FSA???
I hear people saying "crank the bolt down really hard and that will keep it tight".
Is that a good idea? Or is there no bearing pressure on their cranksets??
I'm a bit confused. Then again I'm from the U.S. I agree, kind of ugly, but ugly and
function sometimes go together.

Dennis Noward

alfablue

It is surely the thread in the BB or the bolt, rather than the crank. I suggest threadlock too, then a new bolt, then a new BB.

topdude

Hi, the crank bolt will not come loose unless there is movement between the crank and bottom bracket axle.
Maybe the two square tapers are not a good match or maybe it is just not tight enough.
One thing you could try is to remove the crank arm, clean both mating parts, put a light smear of grease on the axle, refit and tighten well but not ridiculously tight.
This should allow the parts to slide together with a closer fit and hopefully not work loose again.
Regarding the Hollowtech outboard bearings and cranks i also think they are the dogs wotsits, a brilliant and simple design.

geoff_ss

On the odd occasion I've had cranks come loose the only solution was to replace the crank. The bolt will only come loose if there is movement between the crank and the bottom bracket axle and that is always because the crank is damaged.

My only experience has been with square taper axles but I'm sure it applies to other types.

Geoff

Fat Head

i had my left crank come off repeatedly on a cheapo bontrager chainset that came with my first road bike.....it once left me strand in deepest darkets essex and thankfully a kind lad gave me a lift home in the back of his van....not fun.....treat yourself and buy a decent chainset, something like a shimano 105?

thetrotter

See the attached:

http://www.sheldonbrown.com/brandt/inst ... ranks.html

nickcuk

Depends how badly the square on a square taper crank has deformed - the crank is alu because it's lightweight but it also deforms instead of wrecking the axle. If the square of the crank has deformed too much and/or the bolt is not tightened enough, the normal peddling action will gradual loosen the bolt (there's a technical name for this).

First thing - lube and tighten up the existing bolt for the existing crank with a long extension fitted to a good quality allen key and give it some welly over a couple of miles round your home. If you find any looseness at all, replace the crank and do the same again. if the left crank is still working loose then you are either not tightening enough or the thread on the axle is u/s and that's a bigger job.

AndyGates

Nick is wise: the crank gets chewed up as it works loose, and once it is chewed up, it will never sit properly again.

A properly fitting, properly tightened crank doesn't need threadlock. But you do need to mongo the bolt good and tight.

Replace the crank, and do it up tighter next time. If the bike was new from the shop with this problem, it's a warranty job as proper tightening of the cranks is part of the pre-ride check.

ijportwine

Thanks a lot for the advice, greatly appreciated