Square taper damage - how much is too much?

[Brian73]

This left hand crank was hanging off the bottom bracket spindle. It had been ridden like this by the previous owner

I have tightened it up back onto to the spindle, but didn't wan't to risk riding it myself

How robust are the tapers when damaged?

[fastpedaller]

That's scrap. I've had ones a lot less deformed that would never work again - by the time you feel it's loose the damage is done unfortunately.

[Keezx]

That's certainly too much, far beyond repair.

[mercalia]

if you can get some thinnish alluminium sheet you might be able to make a sheath to fill in the gaps?

[CREPELLO]

if you can get some thinnish cheese sheet you might be able to make a sheath to fill in the gaps?

FTFY

[[XAP]Bob]

Virtually anything is too much.

The only redeeming quality is that you can probably do the bolt up hard and ride it to a shop to get it changed - the damage will continue to the (already scrap) crank, not the square taper...

[Brucey]

The OP's crank is basically scrap.

However just for fun, I have once or twice filed out a taper that was damaged like that. Once you have filed a bit, you can test the fit of the parts and file some more until they fit reasonably well. To some extent the crank will 'size itself' to the BB spindle if the parts are greased and the torque is made 'more than normal'. If you are prepared to retighten/file again as necessary, you can have some hope that the parts can be made to work. However it is rarely 'worth it' in terms of time expended.

If you are to attempt this, it is as well to be aware of the various issues;

1) precision; you need to be very good at using a metalwork file!
2) taper pull-through; you can pull the BB spindle too far through the crank; it may be necessary to use a spacer for the crank bolt not to bottom out
3) taper pull-through; you may run out of taper on the BB spindle
4) pull-through effect on BB length; you may need to fit a longer BB to get everything to work
5) swash alignment; a re-filed RH crank is extremely unlikely to run true, not well enough for front derailleur use anyway. I have used a re-filed RH crank on a single chainring bike.
6) pedal spindle alignment: whatever swash misalignment there is will also afflict the pedal spindle alignment too; you might as well have bent pedal spindles....
7) radial alignment; again unlikely to be perfect, so problematic for RH cranks on singlespeeds
8 ) 'timing' alignment; the new square may well be rotated wrt the original one; this means that the cranks probably won't be timed at 180 degrees like they ought to be. [If you ride enough on such cranks, your pedalling style will eventually be ruined IMHO]

Obviously a LH crank has fewer issues than a RH crank, but then a LH crank isn't such an expensive or difficult thing to replace anyway.

cheers

[mattsccm]

Work out how much room is behind the crank with at least one turn of the bolt in. Fill gap in taper with bits of alloy eg folded drinks can or thin alloy sheet. Start the whole affair with a few taps off a hitting stick then dog the bolt up tight. It'll stay.

[rjb]

I put a worn crank back on with some thick aluminium foil cut from a disposable pie tray wrapped around the square axle. There should be lots around in a couple of days time once the turkey is done. Yours looks quite bad but it probably owes you nothing so you have nothing to lose. Merry Xmas, hic!

[fastpedaller]

Put old crank in bin - any packing out or tightening up will prove a waste of time . Go to bike shop and buy a new crank and get them to fit it or do it yourself to the correct torque.

[mattsccm]

Come on. Fail before giving up.

[Brian73]

I had a spare crank in the shed, but it was 175mm and black, not 170mm and silver.

I had no intention of using it like this, it's an Ofmega Vantage 42/52 set, bit too tough for the hills here. So will probably just sell the spider and rings separately instead of sell it as a complete chainset

[[XAP]Bob]

When my left crank fell off a few miles into my commmute I carried on into town ATM lunch and got a crank from the parts bin. Had one black and one silver for ages... (the bike is stripped at the moment)

[Cyril Haearn]

Is it dangerous? Could it suddenly snap?

[[XAP]Bob]

It won't snap, it will just come loose pretty fast.

It will feel floppy for a short while and then fall off - but you'll have had fair warning.
If you use cleats then ride the rest of the way to the lbs with one foot...

Hence my original - do the bolt up hard and it might get you *gently* to the lbs.