r/h crank arm thread f****d

[albal]

Hi,
picked up a spesh rockhopper the other day & the thread s gone on the drive side crank arm, looking through old threads , i notice this can be rectified if one screws in pedal from the inside? this cuts a new thread allegedlly. Its a right hand thread on the drive side i think. Anyone confirm this?

 

[Zoiders]

You can use a pedal as a tap as the quick and brutal method, or just get the bike shop to do it with a proper Park tap for pedals.

If it's too far gone it's either a new crank arm or if it's a pricey chain set then possibly get a thing called a "Helicoil" fitted which is a stainless steel insert that replaces the aluminium thread, it's a work shop job though as the pedal hole needs reaming out before hand to take it.

 

[Rhythm Thief]

if you're reasonably competent with a drill, and you own a sufficiently large drillbit and a vice, you should be able to do a helicoil yourself. But I'm not convinced it's a great idea for something as critical and load bearing as a pedal thread. I'd just start scouring ebay for another chainset.

 

[gbb]

Driving the pedal through from the other side might recover some thread, but as the pedal's slowly (i assume) worked loose, its likely the threads have been damaged along the whole length. It'd possibly give you a temporary repair, but i wouldn't give it much long term given the stresses on the cranks.

Helicoil ? I use them at work although not on such high stress areas. The downside is helicoils are expensive as kits, assuming you can find the right size. Preparing a damaged crank would be easy, the kits have the correct size drillbit, an oversize tap and of course the helicoils. The operations quite easy..perhaps your LBS will have the right size saving you the need to buy an expensive kit.

If it were my bike and having recovered the threads with the pedal...if it seemed a good tight fit , i'd put some high strength loctite in there as well if it were an older bike. If its my pride and joy, i'd probably gulp and buy a new crank or see the LBS about a proper repair.

 

[Gerry Attrick]

if you're reasonably competent with a drill, and you own a sufficiently large drillbit and a vice, you should be able to do a helicoil yourself. But I'm not convinced it's a great idea for something as critical and load bearing as a pedal thread. I'd just start scouring ebay for another chainset.

There is nothing wrong with a Helicoil for pedal application. If correctly installed, the thread is far stronger than the original. Such coils are widely used in industry for critical load-bearing applications. I regularly used them in restoring vintage motorcycles including the repair of cylinder head threads which are placed under far more load than a pedal.

 

[2Loose]

There is nothing wrong with a Helicoil for pedal application. If correctly installed, the thread is far stronger than the original. Such coils are widely used in industry for critical load-bearing applications. I regularly used them in restoring vintage motorcycles including the repair of cylinder head threads which are placed under far more load than a pedal.

+1 one of my old motorbikes had the entire rear seat and tail assembly mounted onto threads reclaimed by helicoil in alloy. Nothing to worry about in a load bearing situation at all.

 

[david1701]

I would advise against home building one without a jig/lathe though

as if the drill is off perpendicular the crank will go crazy

 

[Rhythm Thief]

I would advise against home building one without a jig/lathe though

as if the drill is off perpendicular the crank will go crazy

That's what I meant. I've repaired various engine bits myself with helicoils, but in most of the applications I've used them for it doesn't matter if the thread's on the piss a bit. If you got it wrong with a pedal thread, it'd be a bit more serious.

 

[Alun]

I had 2 helicoils done in some MTB forks for £10, better than new !

 

[Zoiders]

I had 2 helicoils done in some MTB forks for £10, better than new !

What he said.

I used to sell helicoils and they are not an expensive item of iron mongery on there own without the kit, a good fixings place will stock them or can order them in on a next day delivery.

A good frame builder or manufacturer like Goldtec has the kit for fitting such as a press drill and the taps.

A helicoil will not weaken a chainset it will in fact strengthen it, some MTB specialists offer it as a complete upgrade for chain sets for the pedal drillings and also as a chain ring bolt replacement if the spider is chunky enough, a lot of higher end off road chainsets come with stainless thread inserts for the pedals as standard now.

 

[albal]

yes thanks guys, i did re- cut it from the other side & it seems ok. It probably worth buying a new 'spider' for the suntour crankset. Are these readily available?
The crankset along with the bike is virtually new & would be a shame to bin it. Where do i enquire about helicoils? LBS? he is closed this week

 

[Zoiders]

Spider just means the holes that the chainring bolts to - don't worry about that.

If the LBS gives you no joy ask a motor bike garage, it's a quick job for a skilled fabricator.

 

[gbb]

What he said.

I used to sell helicoils and they are not an expensive item of iron mongery on there own without the kit, a good fixings place will stock them or can order them in on a next day delivery.

A good frame builder or manufacturer like Goldtec has the kit for fitting such as a press drill and the taps.

A helicoil will not weaken a chainset it will in fact strengthen it, some MTB specialists offer it as a complete upgrade for chain sets for the pedal drillings and also as a chain ring bolt replacement if the spider is chunky enough, a lot of higher end off road chainsets come with stainless thread inserts for the pedals as standard now.

While this is true, its not the helicoil itself that costs, its the tap that'd cost IRO £10 to £15 and unless youve got the right sized drill...another £5 roughly (prices based on engineering quality products)

 

[Zoiders]

While this is true, its not the helicoil itself that costs, its the tap that'd cost IRO £10 to £15 and unless youve got the right sized drill...another £5 roughly (prices based on engineering quality products)

Yes we are aware of that.

Thats why we said go to a workshop that has the kit.

 

[gbb]

What he said.

I used to sell helicoils and they are not an expensive item of iron mongery on there own without the kit, a good fixings place will stock them or can order them in on a next day delivery.

A good frame builder or manufacturer like Goldtec has the kit for fitting such as a press drill and the taps.

A helicoil will not weaken a chainset it will in fact strengthen it, some MTB specialists offer it as a complete upgrade for chain sets for the pedal drillings and also as a chain ring bolt replacement if the spider is chunky enough, a lot of higher end off road chainsets come with stainless thread inserts for the pedals as standard now.

Yes we are aware of that.

Thats why we said go to a workshop that has the kit.

You did say..'a good fixings place will stock them or can order them in on a next day delivery'
I took that as a suggestion to OP, when of course he might not have understood the total cost is not just about the helicoil itself (if he brought them) and that it would be the LBS that'd order the helicoils..not OP
Hey ho..no problem