crank play

i have noticed that there is a small amount of play on my cranks no matter how tight i do them up! its almost like the hub is too small (although its not) any idead how i can stop this or shal i get it re-built?

any ideas would help. bungle

Re: crank play

What kind of cranks do you have? Is your hub splined or tapered? What kind of play is it?

they move backwards and forwards while im riding, not side to side. the cranks have square holes in them tomatch the hub.

Is the looseness at the bearings or is it at the cranks, or least likely is there play in your pedal. If the bearings are loose or worn, it won’t matter how tight you tighten up the cranks.

its definatly at the hub and not the bearings the bearings are fine.

Your cranks are deformed. The hole should be EXACTLY square, but because they were ridden on while a little lose the metal near the corners has been pushed out a bit so the tapered surfaces now bulge slightly in the center. These surfaces should make full contact with the tapers, but since they are bulging only a small patch near the center touches. When you pull back and forth on the cranks tthe bulge rocks back and forth on the spindle flats and you perceive play at the pedals.

The only way to reduce the play is to straighten the “rockers,” i.e. the formerly flat surfaces inside the crank hole, but just setting up the machinery to do this properly is going to be really expensive. (And that’s if you have access to a high-quality machine shop.) Unless you plan on doing a production run of hundreds of cranks it just isn’t worth it.

The only practical fix is to buy new cranks - with factory flat surfaces - and get them professionally installed. Any good LBS can do this for you. Ask if you can watch while they install them. It’s possible that they won’t use a torque wrench to put your cranks on, but that’s only because they’ve done so many their hands are calibrated. You should use a torque wrench.

Re: crank play

“cyberbellum” <> writes:

> The only practical fix is to buy new cranks - with factory flat surfaces
> - and get them professionally installed.

I’ve fixed slightly damaged crank tapers by carefully filing them with
a square file (part of a $6 set from Harbor Freight). Obviously, it
is easy to ruin cranks this way, but if you are careful it is possible
to repair them in some cases.

These were $12 Torker cranks which are soft, easy to file, and no
great loss if I messed up.


Re: Re: crank play

Good point. If they’re ruined anyway, what have you got to lose?

I’ve been wondering if carefully filing down the middle third of the flat would be enough. That way all the pressure is taken up near the corners where it belongs.

The way I would do this is to:

a) get the crank hole really clean with a solvent of some sort. Clamp the crank gently in a vice so it doesn’t move around when you do the following steps. Wrap it once or twice with a shop cloth first so it doesn’t get scratched.
b) Use an indelible marker to coat the inside of the crank hole with a thin coat of dye.
c) Carefully measure and mark the middle third of the flats at each end of the hole. Using a straightedge, connect the 1/3 marks at each edge of the flat with a small, sharp knife or pin. Lightly cut through the dye to scribe two boundary lines on each flat.
d) Carefully (checking often by eye and by feel) file down the center section with a rounded file until all the dye ibetween the lines is gone and you can feel (barely) a slight depression in the center. The dye outside the lines should not even be scratched.
e) Clean the dye off with a solvent. Wipe out any particles.
f) sand lightly with a very fine grit paper (600 or better) to remove any obvious burrs. One or two passes should be enough.
g) Clean again with solvent. Buff with a soft cloth.
h) Mount the crank as usual. Blue loktite if you like.