Loose Crank

Hi Everyone, I am new to road riding and have just got myself a 1978 Coventry Eagle on eBay. I am pleased with the bike (admittedly I have nothing to compare it with) but after a few weeks riding, the left crank fell off. The nut came off somewhere on my commute and therefore I fitted a new one. My 14mm socket does not fit on the crank nut well so I am unable to tighten it enough to stop the whole crank arm wobbling. Do I need a different tool to tighten it fully? Or do I need a new crank arm? For reference, it is this type of nut/crank setup Any help is appreciated!

 

First, you need to make sure the threads of the replacement nut match the threads (size/pitch) of the crank bolt. If not, you can strip the bolt threads which will create a bigger problem.

Once you have identified/confirmed you have the correct nut, then you will want to use a combination of proper torque and thread lock compound or lock washer to retain the nut. If you don't have a socket or wrench to properly fit the proper nut, then yes you will need the proper tool to prevent "rounding off" the nut.

 

The nut was off another bike for the crank on there. Does that mean the pitch will be correct or is it not guaranteed?

http://www.evanscycles.com/products/ice-toolz/crank-removal-tool-with-handle-ec006782

Does that look like the right sort of tool? My socket set is not doing the job and like you have pointed out the nut is becoming rounded off.

I have read elsewhere that cranks become damaged if they have been ridden loose. If this is the case do I need a new bottom bracket or just the crank arm itself?

Thanks for your help.

 

Not guaranteed, but could be OK. Depends if the bottom bracket (axle) was the same - I'm not familiar with your bike brand, so don't know what BB you have. Got a picture?

Loose cranks can round the square taper of the axle if that's what you have. Can round the crank arm opening also. Best not to ride with crank loose.

P.S. that's the right tool for pulling the crank, but not necessary for tightening.

 

you are going to spend more money fixing that bike than you would buying another one

 

FWIW. It sounds as though you have damaged the receiving mortise for the square taper on your BB's spindle ...

As sitzmark suggests, it is best not to ride with a loose crank ...

A remedy which is not particularly expensive is to SHIM the BB's taper so that the crank arm can be snugged against the spindle ...

• the shim can be cut from either BRASS STOCK or a TIN CAN ... you need to be moderately careful since the edges of the metal may be sharp enough to cut you
• so you will want to round them with emery cloth or a file

[*] fold over the spindle's taper so that you create a "saddle" which will drape over two sides of the taper ...
[*] trim (again, you want to ensure that the edges are 'clean')
[*] apply a light coat of grease
[*] sleeve the crank arm onto the shimmed taper
[*] tighten

If you cannot adequately shim the crankarm so that it doesn't wobble, then you will need to replace the crankarm and/or crankset & BB.