Rethreading a stripped crank arm

[Twilkes]

Has anyone had success rethreading the pedal thread on a crank arm using one of the sleeve inserts and a reaming/tapping tool?

What insert/tool did you use? Some seem to be £5-10 each, others are a kit for a few hundred quid so I'm not sure if the cheap ones would do as good a job? Did you do it on the bike or in a vice?

I've fitted a new chainset on my bike anyway, this was just to salvage something from the old one rather than binning it. it's a SRAM Rival 22 so worth saving, although I can re-use the chainrings anyway and the spindle is on the non-drive side which is still fine.

 

[battered]

For a one-off I would get a local engineering company to do it, or maybe a LBS. I had a crank arm stripped when I lent my bike to a pal and he cross threaded a pedal. Fortunately I was able to screw the pedal in from the other side, this restored the threads enough to work again. I refitted the pedal with Loctite and made very sure that I never had to remove the pedal again until the Octalink BB wore out and I replaced the thing with something sensible.

 

[fossyant]

I wouldn't bother, too much at risk here. If it comes out, you are chewing tarmac !

 

[T4tomo]

how badly is it cross thread - and how did you manage it - its quite difficult as pedal threads are quite deep compared to say bottom bracket threads, if you start them off with fingers / allen key from the reverse side its virtually impossible to cross thread?

the old screw thru from the other side trick might work.

 

[Sharky]

can recommend these people
https://highpath.co.uk/

I have had two pairs of cranks completely re drilled - have had no problems.

 

[battered]

I wouldn't bother, too much at risk here. If it comes out, you are chewing tarmac !

It's got to go some to come out once screwed in. About 15mm of threading, how is it going to fall out? Only by unscrewing the full 15mm, and the threads are handed so they tighten under pedalling. If it's so bad that it can fall out, it won't tighten up in the first place so you will know.

 

[Twilkes]

how badly is it cross thread - and how did you manage it - its quite difficult as pedal threads are quite deep compared to say bottom bracket threads, if you start them off with fingers / allen key from the reverse side its virtually impossible to cross thread?

the old screw thru from the other side trick might work.

It was fitted months and hundreds of miles ago but I remember the pedal being quite hard to get off the old crank, so I wonder if the thread on the pedal was damaged during that (they were already old pedals) which then damaged the new crank thread on the way in, and it's just been fretting away at it since then. Between me feeling there was some 'play' under my feet (I thought the cleat was loose) and the pedal coming off was about 5 miles/15 minutes.

I can push a new pedal about 80% of the way into the crank without it catching the thread so it might be totally gubbed, but if a tool and sleeve is £20ish, which it looks like it might be, then it's worth a shot.

 

[fossyant]

So the pedal will go in 80% without 'threadding' - just get new. I don't mess with cranks and bars/stem, really not worth a fail.

 

[gbb]

For general consumption, its very very important when inserting into aluminium threads, make absolutely sure the item you're threading in is absolutely clean and free from debris such as aluminium shards. These prevent the free travel in the threads, making the item (pedal usually) very tight to get in and once its started, that shard (even a tiny one) just eats into good threads.
I always carefully inspect pedal threads BEFORE even trying to insert them into cranks, the tiniest pickup of aluminium on old pedals can wreak havoc.

 

[battered]

It was fitted months and hundreds of miles ago but I remember the pedal being quite hard to get off the old crank, so I wonder if the thread on the pedal was damaged during that (they were already old pedals) which then damaged the new crank thread on the way in, and it's just been fretting away at it since then. Between me feeling there was some 'play' under my feet (I thought the cleat was loose) and the pedal coming off was about 5 miles/15 minutes.

I can push a new pedal about 80% of the way into the crank without it catching the thread so it might be totally gubbed, but if a tool and sleeve is £20ish, which it looks like it might be, then it's worth a shot.

For less than £20 (probably half that) a local engineering company will fit an insert. Then you know it will work, and you know it will be right. For an engineering company this is teabreak stuff, it's their bread and butter and they can do it perfectly all day long.

 

[silva]

For general consumption, its very very important when inserting into aluminium threads, make absolutely sure the item you're threading in is absolutely clean and free from debris such as aluminium shards. These prevent the free travel in the threads, making the item (pedal usually) very tight to get in and once its started, that shard (even a tiny one) just eats into good threads.
I always carefully inspect pedal threads BEFORE even trying to insert them into cranks, the tiniest pickup of aluminium on old pedals can wreak havoc.

Yes. Aluminium isn't as elastic as steel - it doesn't "give" to then "return", it "gives" as a hair crack, that grows, gives play, exaggerating it, till catastrophic (sudden) failure. The damage progress in alu thread is fast.

 

[Ajax Bay]

Aluminium isn't as elastic as steel

In the materials' elastic ranges, I suggest aluminium is more elastic than steel: for a given load/stress (tension) it elongates more: about 3 times as much. On the release of stress the material returns to exactly its original dimension: it does "give" and then "return" (in its elastic range).
Perhaps that's what you meant. Or maybe you were not talking about elasticity but about material behaviour beyond the linear stress/strain range.