Repairing busted pinch bolts?

[Tribal Chestnut]

Two outer bolts on forks have been cross threaded at some point and I’ve made them worse with my attempts to get bolts back in.

I’ve never repaired a thread before.

Any advice?

Do I need one of those helicoil things or can the threads be recut/tapped?

Removing the forks isn’t an option due to time and space, so whatever I do need to be done with the forks in-situ.

Due to time constraints any tools I need must be available OTC from my local Screwfix or Toolstation.

Thoroughly p***ed off.

[Error_404_Username_not_found]

Helicoil is very good IF....
There's enough metal because it will have to be drilled oversized (for example 8mm Helicoil requires 8.3mm drill, which should be in the kit).
And...
If you know what you're doing with them. It's quite easy to do but it's also easy to c*ck it up.
Helicoils are specced by nominal thread x length in multiples of the diameter.
Example: 8mm x 1.5D where the screw diameter is 8mm and the installed length is 12mm.

Edit: other brands are available but original Helicoil gets my vote. The tools needed should be in the kit i.e. special drill, special tap and installation tool. As always, RTFI.

Edited by Error_404_Username_not_found on Thursday 29th September 14:51

[black-k1]

You might be able to clean up the existing threads by carefully using a tap. Easy to try.

[Krikkit]

black-k1 said:

You might be able to clean up the existing threads by carefully using a tap. Easy to try.

This first ^^

Then this:

Error_404_Username_not_found said:

Helicoil is very good IF....
There's enough metal because it will have to be drilled oversized (for example 8mm Helicoil requires 8.3mm drill, which should be in the kit).
And...
If you know what you're doing with them. It's quite easy to do but it's also easy to c*ck it up.
Helicoils are specced by nominal thread x length in multiples of the diameter.
Example: 8mm x 1.5D where the screw diameter is 8mm and the installed length is 12mm.

Edit: other brands are available but original Helicoil gets my vote. The tools needed should be in the kit i.e. special drill, special tap and installation tool. As always, RTFI.

If you've got enough room of course, helicoil will likely be stronger than the original aluminium in the forks. The original branded ones aren't too silly and as noted they are a touch stronger than the cheap copies.


Alternatively, you could see if there's any mobile thread repair outfits near you - they're surprisingly common, not silly money, and guaranteed to get a good result.

[AceOfHearts]

helicoil will be no good for fork pinch bolts if you want to do it in situ, as you have to drill oversize and tap it to the new thread size, meaning you will probably end up tapping the plain part of the triple clamp which would be a total bodge up. Best thing is to try and clean up with the correct sized tap and make sure the pinch bolts are also in good condition otherwise it will just bugger up the threads again.

If this fails you really need to take them apart and do the job properly. You don't want to hit a bump one day and the forks slide up in the clamps!

[Error_404_Username_not_found]

AceOfHearts said:

helicoil will be no good for fork pinch bolts if you want to do it in situ, as you have to drill oversize and tap it to the new thread size, meaning you will probably end up tapping the plain part of the triple clamp which would be a total bodge up. Best thing is to try and clean up with the correct sized tap and make sure the pinch bolts are also in good condition otherwise it will just bugger up the threads again.

If this fails you really need to take them apart and do the job properly. You don't want to hit a bump one day and the forks slide up in the clamps!

This is true, and good advice if the tapped holes are blind. If they are through-tapped no problem. Do them from behind.
Are they the pinch bolts at the top (triple clamps) or the bottom (spindle clamps)?
Pictures might help.

[underwhelmist]

black-k1 said:

You might be able to clean up the existing threads by carefully using a tap. Easy to try.

The thread that my front wheel spindle threads into had been abused (by a previous owner, obviously!), I bought a secondhand spindle which turned out to be in better condition than my original, but it still wouldn't go in. I cut some slots in the original spindle with a Dremel to make a thread chaser, that cleaned it up a treat. Worth sacrificing a bolt if you haven't got a tap.

edit: like this - if you try it put a drop of oil on it before winding it in, and back it out occasionally to get rid of any crud.

Edited by underwhelmist on Thursday 29th September 18:07

[Tribal Chestnut]

Seems I have a different problem.

A re-tap and swapping the bolts from another bike has sorted one side, but the right hand seems to have a misaligned thread where it passes through the fork lower from one side to the next.

It’s almost as if something has struck it from below, forcing one half out of alignment.

I could only see this by fitting the bolt from the rear, so it’s quite clear where the alignment issue is.

Looks like I’ve another shagged bike.

Anyone want a cheap day at Brands on Monday?

Middle group, paid £125 will take £70.

[Tribal Chestnut]

Thanks for the advice on sorting the thread issue anyway chaps.

[Abdul Abulbul Amir]

Do you still have the mt10?

[Tribal Chestnut]

Abdul Abulbul Amir said:

Do you still have the mt10?

Thought about that, but I’d definitely fail noise.

Also needs remapping, so not keen to ride it hard until that’s done.

Fettling the exhaust system to get it usable isn’t an option in the time available, plus I think I’ve used up all my available reserves of patience until the NY.

[Tribal Chestnut]

I at least managed to fk it properly.

Had the impact wrench ready to go, but the bolt started to tighten ok, popped the torque wrench on it and this happened:

[Krikkit]

Bugger

[black-k1]

That's a double ouch!

[Tango13]

Tribal Chestnut said:

I at least managed to fk it properly.

Had the impact wrench ready to go, but the bolt started to tighten ok, popped the torque wrench on it and this happened:

How thin is that casting around the thread?! I think you've done yourself a big favour fking that up 'cos the lack of metal there is seriously dodgey!

[Error_404_Username_not_found]

Tribal Chestnut said:

I at least managed to fk it properly.

Had the impact wrench ready to go, but the bolt started to tighten ok, popped the torque wrench on it and this happened:

Hard to tell from the image on my tablet but it looks like you were on a hiding to nothing anyway. It looks to me like there was already a coil-insert thread in there which wouldn't surprise me, given the skimpiness of the casting. It would have been a pure bastage to get out - no way in the world could you have drilled it.
That's proper bad luck mate.

[Tribal Chestnut]

Yep, as a positive at least it didn’t go just before my trip to Portimao, at the height of summer, or maybe even whilst on track.

And I’ve discovered that tapping threads and tidying slightly mangled bolts is not so daunting and actually quite good fun.

[Tango13]

Tribal Chestnut said:

Yep, as a positive at least it didn’t go just before my trip to Portimao, at the height of summer, or maybe even whilst on track.

And I’ve discovered that tapping threads and tidying slightly mangled bolts is not so daunting and actually quite good fun.

One of our CNC machining centres can tap at 6,000rpm so tapping an M6 will see the spindle going 6k whilst feeding into the part at 6 metres a minute before stopping, pausing for 0.1 of a second and coming back out just as quick.

For the bigger threads like 1" BSW we generate the thread by milling a spiral with a thread forming tool.

When we got the machine the programmer refused to set it as he had a dodgy heart and reckoned it would finish him off.