Help! Threaded my left hand crank pedal threads

[David9694]

Managed to get home by inserting the pedal from the inside to catch the remaining good threads. It’s about three- fifths gone. Can’t understand how this happened.

Will attempt to re-cut the damaged threads in the week, but that has a 50/50 chance of success. Then there are the sleeves (SJS sell them) but you need a 5/8” 24 TPI tap for these, £139 to you Sir.

i’ve Found a tap on EBay that looks like it’s the right one for the sleeve bushings, (link below) which are reasonably priced in themselves, so I could follow the procedure on the Park website. I assume the outer threads of the bushings are.also l/h thread?

Has anyone got any advice or experience of this please?

https://www.ebay.co.uk/itm/5-8-24-HSS-L ... 0677.m4598

[NATURAL ANKLING]

Hi,
You just need your tap and an insert for left hand thread.
Perhaps buy a spare insert, also try and track down inserts from another supplier that might be cheaper?

For aluminium pedal crank you need some cutting fluid (rocol / similar thread cutting fluid compound, like a grease constituency ) Failure to use cutting compound fluid will be disastrous, thread will be too big!

Tap
Insert
Cutting fluid
Tapping drill
Tap wrench
insert tool which you could make (there a bit of knack in inserting insert)
Ideally a pillar drill and good vice
Some patience.
If you have not tapped holes before could be a bit tricky

If you get parts a metal working firm would do job but it might still be pricey for their labour.

Good luck.
Get quotes / new crank?

[gaz]

Highpath offer crank thread repairs.

Edit:typo

[rjb]

If you managed to fully insert the pedal from the inside of the crank then this would have cleaned up the thread. Using a tap would not make an appreciable improvement to the thread. You could then put the pedal back on from the correct side and see how you get on. If it comes loose it could indicate the crank is terminally damaged. Probably cheaper to get a new left hand crank than have a repair using thread inserts.

[gxaustin]

Is it cheaper to look for a crank on Ebay? Or is it very special? I invariably buy s/h crank sets for less than £30.

[dsmithave]

If you're keen to repair Ceeway offer a tool which reams & taps in one to put in a repair sleeve. Total cost fairly modest but may be more than a cheap crank.

I believe it's item 229 here in the "economy tools" section:
http://www.framebuilding.com/economy%20 ... ilding.htm

I used one for a tandem crank, without any tools except a tap handle and some lubricant If I remember rightly. It wasn't challenging & involved about an hour pottering in the garage getting everything together & doing the job. The repair sleeve seems happy where it is and has survived well.

It's not necessarily a tool for a production workshop but it worked for me and there seems no reason the fix would be weaker than the original threads.

[David9694]

The l/h 7/16”pedal tap made only a superficial difference. I’ve ordered a 5/8” l/h tap from China for £15, so I’ll see how that goes. It’s an Ultegra crank so worth trying to save. Bike Inn have new FC 5800 for £39 delivered if all this fails.

Wish I’d though of Framebuilding.com first!

[David9694]

Update : the 5/8” l/h tap has arrived from China.

With some cutting oil, and a tap handle it was simple enough to cut the enlarged hole with crank secured in my work stand. Not 100% sure how square it is. I’ve ordered a left-hand a helicoil insert from SJS and I’ve got some threadlock lying around.

[lescargo]

What length and model crank do you need?

[David9694]

What length and model crank do you need?

Ultegra 6800 in black 172.5mm

I’ve seen a crankset on Planet X for £34 that I might cannibalise.

[David9694]

..and that was a failure,

The helicoil preferred to self-destruct rather than be screwed in to my lovingly re-cut hole (5/8” l/h 24 TPi, since you ask). It screwed nicely around the pedal arm but literally recoiled at the thought of going into the crank.

What have I done wrong here?

[Brucey]

if the insert is the standard (spiral wound) type then it ought to be fitted using an appropriate tool, which is usually one with a slot that engages with a (snap-off) tang in the centre of the insert, like this;



This 'pulls' the insert from the bottom and makes sure that it doesn't turn into a birds nest as it is fitted, which is exactly what will happen if it is wound in from the top.

If you didn't use a tool like that, could that be the reason it didn't work for you?

cheers

[Mick F]

I did a course on Helicoils many years ago in the RN.
It was a part of a teleprinter course. The bases were alu with the teleprinter mechanics bolted to it. They stripped from time to time, mainly due to the vibration of running them at 75 bauds so they needed to be tight. We used Helicoils to repair them and I remember the tool kit they came in. Various sizes and lengths, and you do indeed need the insertion tool.

The kit consisted of special sized drills and taps as well as the coils and tools.
The tool made the coil "shrink" in diameter as the coil was inserted, then you broke off the tab, and hey presto, you had a new thread.

[thirdcrank]

I am generally useless or worse than useless with technical stuff. In recent years I've found youtube an invaluable source of information in visual format which is an excellent way of learning so long as you pick the right vid. There seems to be a selection here
https://www.youtube.com/results?search_ ... il+inserts
Perhaps somebody who knows will recommend one as being useful.

[David9694]

Thanks folks for the responses. The SJS/VAR helicoil didn’t have a tang - I can see the sense of a tang for contacting the helicoil, now you mention it. There are plenty of M sized helicoils available as kits with the tang and a tool - us and our imperial sizes, eh?

The procedure I followed was https://www.parktool.com/blog/repair-he ... -procedure

See figures 7 & 8 in particular: 6 run the repair tap through (check); 7.thread the helicoil onto the pedal (check); then 8. screw the whole thing into the crank, step 8 being where it went wrong for me.