Crossed Thread - Bike Pedal

When assembling Mrs Baci’s new exercise bike it seems I might have crossed a thread when screwing a pedal into the crankshaft thing. How can I remedy this? How do I know what the thread dimensions are so I can pick up the right tool. What might that tool be?

Bikes usually have a left hand thread on one pedal. This means instead of turning clockwise to install it, you turn it counterclockwise. Hopefully this is your problem. If not you will have to take the pedal with you to find the right tap to rethread the hole. If you know any machinists or mechanics they should be able to find the correct tap and fix the threads for you.

You will need a tap. Start the tap from the back side of the crank on the good threads. A little lubrication will be needed too. Use a back and forth method to run the tap through the crank, 1/4 turn in, back off 1/8, another 1/4 turn, etc. If the threads on the pedal are screwed up, you will need a corresponding sized die. As for the size, that would be hard to say. Take the pedal to a decent hardware store, they will have what you need.

You didn’t try to put the left hand pedal (with it’s left handed threads) on the right side? Or right into left? And if you messed up the left hand threads, expect a tap to be difficult to find. Last time I needed a left hand threaded tap it cost me $45 at a bike shop, the same right handed tap would have been 7 bucks.

Measure the outer diameter of the male threaded part, then measure the pitch with a thread gauge. The result should be something like 3/8" x 24 or 8mm x 1.25. Calipers are best for the O.D. measurement, and you should have both metric and U.S. thread gauges.

First choice would be a rethreader (a.k.a. thread chaser, thread restorer) tap and die. These are designed to reform damaged threads and usually work quite well. Alternatively, a regular tap and die would be effective, but work by cutting metal away and thus might weaken the threads some.

Another thought. You might take it to a bike shop to have it fixed. That might be cheaper than buying a tap.

if you damaged the right hand threads there are taps or thread chasers to use as described.

if you damaged the left hand threads (left size pedal and crank arm) the tool is hard to find as mentioned. you can carefully use a small triangular file to clean the threads on the pedal. alternately you can remove the damaged threads on the pedal with a flat file at an angle to just remove the small bit of damaged threads. if the threads are damaged on the crank arm you can use a small circular file at an angle to remove just the damaged threads at the start. use small very controlled movements with frequent inspection to see you are only removing damaged threads and not good ones.

this method can also work on right hand threads if you want. you need to do this with small files and lots of control and inspection as you proceed. you don’t need to remove the total thread around the full circumference just the damaged portion.

you can loose part or all of a few threads and be OK. though any thread alteration with any tool demands extra caution when threading the parts together because they won’t start as tightly and make it easier to later cross thread.

if you don’t have the tools or experience hunt up a friend that might. it is not a hard job though it can be costly damage if done wrong.