Crank bolt keeps coming loose. Please help!

[J.Primus]

I left my bike in for a service 2 weeks ago and since I've got it back the crank bolt (thing that holds the pedals in) keeps working itself loose. I notice the shop had threaded the allan key hole so I bought a new one but no matter how tight I tighten it I still find after 10 miles it needs tightening again. Is there anything I can do short of using a hammer to turn the allan key!

BTW the shop that fouled up my bike was Push Cycles on Newington Green. Second time they have done it and the last as I'm not using them again. Avoid like plague. Does anyone know any decent bike repair places in North London.

 

[T.M.H.N.E.T]

Sounds like a stripped thread. Local engineering work type place should be able to clean it up and stick a helicoil in

IIRC 9/16th inch or (14.2875mm) standardized size

 

[Tim Hall]

Do you mean pedal comes unscrewed from the crank, or the bolt that holds the crank to the bottom bracket spindle comes undone? Your description is a bit vague.

 

[J.Primus]

The pedal is coming loose from the the crank as the bolt that holds it in place keeps working loose. I'm not great at technical terms so you'll have to forgive the initial description.