My trusty old M770 3×9 finally died – the drive side pedal is truly stripped, it’s possible to fit & remove a pedal by wiggling it into place…

Has anyone has success repairing (presumably helicoiling)? Is this worth even messing with or should I just accept I’ve had my moneys worth and replace either with a second hand direct replacement or something new?

I’m assuming you mean the crank?. I got a well respected bike repair fella to helicoil mine, didn’t last long, wouldn’t do it again.

Others will tell you helicoil is stronger, I tend to disagree with the theory.

Nobeer – thanks – sorry yes, I mean the crank. Pedal threads are fine.

My experience at work is that helicoiling works great – but that’s related to industrial engines – into cast iron and purely axial loading, nothing like a crank arm so I’d like to hear experiences before going through the expense / hassle of a failed attempt, or worse still having it all fall apart miles from home.

I’ve killed a couple of XT cranks this way and always given up on the idea of helicoil in favour of just replacement. You may get lucky and find a second hand replacement. Someone out there will of damaged the opposite side to you.

Aye, used to work on aircraft engines and we used them on high cost castings as a sacrificial fixing, great on static fixings. As you say, axially fine, but pedals have a fair bit of radial force on them.

You can ream the hole out, re-tap it and fit repair bushes (rather than helicoils).

Bushes are cheap if you know someone with the tool (LBS?)

Alternatively, the reaming / tapping tools are about £25 from Ceeway

I fitted bushes to a set of Raceface cranks that I shortened (to strengthen them), and they’ve been fine for the last ~2 years.

https://www.vartools.com/en/9-16-x20tpi-pedal-thread-repair-kit-var-p396.php

http://www.ebay.co.uk/itm/HELICOIL-Reparatur-Set-fur-Fahrrad-Pedal-Gewinde-Tretlager-Kurbelarm-NEU-/260871016676?hash=item3cbd1fd0e4:m:m22thkMTzhLg1HIUEX-Nv2Q

Crank Repairs and Modifications

Yes, easily done, I’ve done it a few times for customers over the years without any issues, but given the age of the cranks, I’d use it as an excuse to buy new ones.

My helicoil failed very quickly. I just took a crank arm off another set of RF cranks and stuck that on. They are same length but different appearance.. saying that, you can only see one side at a time….

I had to have an XT crank helicoiled because my then teenage son tried to put flats on to sneak out on my bike while I was away. Being a teenager he never noticed the different threads until he had completely ruined one. The repair lasted for years and may still be working but the other son had it nicked while working on London

I bet you can pick up a 2nd hand pair of arms for not a lot more than a repair.

A newer set of slx will be very similar in quality / weight.

Seeing as no one has a non drive sure m770 when i was after one, i have a drive side m770 for not much cash, and postage…

Thanks all – some good info and options there.

The inevitable mental escalation process has already taken place – instead of replacing the cranks with equally old technology, why not get a 1x or 2x option instead. Once doing that it’s probably more effective to buy a drivetrain groupset. Once doing that it’s worth looking at a complete bike. D’Oh!

Anyway, back to reality – teethgrinder, I may be interested in your drive side crank – will drop you an email.

I think I’ve also got something in the garage – I’ll check when back at home, but PM me if you are still in need.

Not sure what you have tried, but when I damaged the threads on a crank I found that fitting the pedal from the wrong side was enough to clean up the thread so that the pedal could be refitted. That was three years ago – I don’t swap pedals often in that bike (so maybe removed and refitted twice in that time) but it has been fine since.

http://www.ebay.co.uk/itm/Shimano-XT-FC-M770-Chainset-Cranks-175mm-Arms-triple-9-10-speed-Hollowtech-2-/272859685656?_trksid=p2141725.m3641.l6368

£70 on ebay looks nearly new plus gets you another set of chainrings.