The dreaded output shaft..... can it be rethreaded?

[SamTomlin94]

Hi all, new to the forums...did know this existed till I went hunting in search of answer to the infamous sprocket nut coming loose...


I'd love more than anything  other have to replace it as the last thing I'd want to do is take the engine and gearbox apart. My question is, is there a die big enough to put a fresh thread on it? Assuming it will be HSS so not sure where to go shopping?!


Thanks all!

[Gnasher]

Yes dias are available. Unfortunately it's not just as simple as rethreading, what's left. I'm assuming your shaft has suffered the usual damage, in which case most if not all the thread has been worn away?

To rethread the shaft, it will need machining down before a new thread can be cut, ie its got to be removed. This will mean the shaft will be smaller in diameter and non standard size ie standard sprocket's won't fit. 

The shaft got to come out either way.  Machining is an added cost to just fitting a replacement.

[SamTomlin94]

    not good news then!!


I've got maybe 1/3 of the thread left (found out after the sprocket slipped off and lost drive on the commute home ).
What's the reasoning behind having to machine the shaft down? I'm not an engineer by any standard so don't understand why the thread can't just use what's already there?

[Gnasher]

A/the thread is cut into the outside circumference a/the shaft.  If the thread has been worn away so has the shaft, to recut a/the thread the shaft must be machined parallel, it will now be smaller i.e. the thickness of what was the thread. The shaft now being smaller in circumference, by definition so will the thread size by a few mm eg was 14, now 12 or whatever depending on what thread is being cut.       

[SamTomlin94]

Thanks for the advice and a good lesson learnt!

[unfazed]

Check out my repair in the downloads section https://foc-u.co.uk/index.php?action=downloads;sa=view;down=43

[Gnasher]

Check out my repair in the downloads section https://foc-u.co.uk/index.php?action=downloads;sa=view;down=43

Nice one worth a try.

It does all depend on how bad the thread/shaft has been damaged though, hopefully in his case no worse than yours

[mechanical music]

drill the center of the end of the output shaft then tap and threadlock a bolt to hold a wide washer/ spacer

[BBROWN1664]

is it possible to drill the center of the end of the output shaft then tap and threadlock a bolt to hold a wide washer/ spacer

Yes

[b1k3rdude]

@Gnasher, Unfazed and Bbrown, nice quick reponse chaps, top marks :-)

[midden]

A/the thread is cut into the outside circumference a/the shaft.  If the thread has been worn away so has the shaft, to recut a/the thread the shaft must be machined parallel, it will now be smaller i.e. the thickness of what was the thread. The shaft now being smaller in circumference, by definition so will the thread size by a few mm eg was 14, now 12 or whatever depending on what thread is being cut.     

Wouldn't the shaft be built back up as can be done with crank journals, before re-cutting the thread

[agricola]

If the thread has worn away, it can be built back up and re-machined but not while still attached to the bike. The shaft must be removed and metal sprayed back to oversize, then machined back to standard. Likely to cost more than a replacement shaft, and the heat applied as part of the process may affect the properties of the shaft. May also affect insurance in the event of an accident investigation involving any failure of the drive components. There are other, imaginative, ways to repair, including welding the sprocket on.

[b1k3rdude]

including welding the sprocket on.

We can't be recomending this as its a temp repair at best, that and its well outside the scope of most riders and it damages the end of the shaft.

Unfazed's method is doable on the bike and allows the bike to be sold on.

[agricola]

including welding the sprocket on.

We can't be recomending this as its a temp repair at best, that and its well outside the scope of most riders and it damages the end of the shaft.

Unfazed's method is doable on the bike and allows the bike to be sold on.

Misunderstanding. I certainly wasn't recommending welding the sprocket on, just pointing out that it can be done. I think its a bodge

[mechanical music]

is it possible to drill the center of the end of the output shaft then tap and threadlock a bolt to hold a wide washer/ spacer

Yes

has this been done before ?

[unfazed]

Check out my repair in the downloads section https://foc-u.co.uk/index.php?action=downloads;sa=view;down=43