How to avoid getting cranky by saving a stripped crank arm
We often get asked by customers if we can repair damaged cranks, specifically where the pedal has stripped the threads from the crank arm. Well we definitely can and regularly do, so we thought we’d put a little blog together for you to see what we do and how the pedal thread repair works.
We use a special tool and some custom made peal inserts to get the job done. You’ll find that it’s always the crank arm threads that get stripped rather than the pedal threads as the pedal threads are usually harder and often the issue comes from the pedal being too loose or cross threaded at some point.
Always make sure your tool is well lubricated before insertion.
We use a specialist tool to ream the old pedal threads out of the crank arm. You can see here how the pedal thread reamer has cut out all of the old threads and left a smooth surface.
The same tool then cuts new threads of a larger size into the crank arm. These threads will be what we thread the pedal insert into.
The above photo shows the new threads beginning to be cut into the crank arm. We wouldn’t normally stop here but it’s a good shot to illustrate what is happening as we cut the new threads.
Here you can see the threaded pedal inserts, cutters for each side crank and the epoxy resin we use to hold the new threads in place. The new larger threads we cut in the crank are the same size as the outside threads on the pedal inserts and the inside threads of the pedal insert are the same size as found on pedals. Simple!
Epoxy resin comes in two parts which we mix on a scrap of cardboard. The mixing of the two parts will cause them to ‘go off’ and become ready to harden.
Smear the resin in the freshly reamed and threaded crank ready for the replacement pedal insert to be wound in.
We wind the new insert into the crank using pliers as it’s a tight fit, on purpose, to ensure that everything stays where it should.
The pedal insert is longer, or wider, than the crank arm in order that you can reach it from the other side to bring it flush on the pedal side to ensure a good, tight fit. Hence the slight overhang on the other side, which is no issue in terms of performance.
And there we go, one expensive set of cranks save from the bin and pretty much as strong as when new.