Stripped chrainring threads on Campag RH crank

[Mick F]

I have a Campag Chorus Triple with a problem.

I bought it a year or more ago, and found to my horror some weeks back that the threads holding the inner chainwheel bolts into the spider were stripped! I loaded super-glue into them in the hope it would hold, but during my checks prior to my Grand Tour, I found they were not holding.

Luckilly, Albion Lass was selling her Campag Comp Triple (basically the same) so I bought it as a 'just in case'. As it turned out, I needed it!

Thank you Albion Lass!

Anyway, now I've returned, I decided to investigate what's gone wrong. To this end, I did a bit of "Show and Tell" down the pub last evening. A few engineer friends go there! We looked at the offending article and found that the threads don't start at the top of the bosses. All five of them!

I've just taken off the Comp Triple from Bike to see how those are.

Here's a couple of shots to show the situation:


This is of the Chorus Triple, showing poor threading.




This is of the Comp Triple. Perfect right up to the top of the holes.


Basically, the chairing bolts only had 3 threads to hold the ring in place, no wonder they've stripped. My mate Paul is going to investigate the possibility of Helicoil inserts or even a better solution - SS insert, drilled and tapped into the spider's arms and then drilled and tapped with the correct threads for the chainring bolts.

Any comments from you out there?

[PW]

That happened to me in about 1985, but the culprits were the other lot
It was the original Deore groupset on a fast tourer just before mountain bikes arrived. The entire group was garbage, I rebuilt the bike in Campag within 3 months and didn't buy Shimano again for nearly 20 years.

[gaz]

I agree that manufacturing the chainset this way was poor engineering and that the solutions you're investigating seem a good way forward.

However wouldn't longer bolts do the trick?

I say this realising that they need at most a mushroom head and without first checking my spare chainring bolt collection to see if they come in a variety of significantly different lengths.

[Colin Stanley]

Mick, Sorry to read about your Campag problem.
That's one deep counterbore on the threaded holes in the Chorus triple. Not having disassembled my Record triple, I have no idea on the configuration of the screws for the granny ring. Do the screws have a plain shank that engages the counterbore to offer the granny ring some location? If they do, then Helicoils can't be used as they are threaded all the way up. You will need to use a bushed threaded insert which also has the counterbore. We used a lot of repair thread techniques at work. Helicoils were ok for normal use. Ready made bushes were better for counterbore applications as they can be machined to suit. There are many on the market, but can't seem to find any at the mo' on a Google search.

Hope this doesn't make you want to change to Sh...NO!

[Mick F]

Hope this doesn't make you want to change to Sh...NO!

NNNOOOO!!!

I bought the C/S from an internet site, I'm fairly sure it was www.bikeplus.co.uk and they had the Chorus Triple at a knock-down price as it was End of Line and shop-soiled. Can't remember the price - but great!

Anyway, it came in it's original box, but with a cosmetic scratch or two on the RH crank. Hey. So what?

Anyway, you can see from the photograph, I reckon it was a Second Quality.

Do Campag do Second Quality? Why not? Other companies do.

Any road up, chainring bolts don't come in longer lengths AFAIK.

I think the threads that are left are suspect, to say the least. If my mate can Helicoil the bushes, I'm positive that the bolts will go in. Remember, the Campag Comp threads go right to the top.

The thickness of the inner ring is quite thick enough to use up any "land" above the threading of the bolt.

Watch this space ..........

[Mick F]

PS

And another thing, can you see the chamfers on the bosses?
What are they for?
A mistake?
Second Quality?

The Campag Comp is flat and flush on all it's bosses.

[pigman]

mickf
you say the 2 chainsets are basically the same. Regardless of quality, there is a very basic design difference. The chorus has only 4 spiders, the 5th being incorporated into the crank.

you also say that chainring bolts only come in one length. Like PW I have (and still use) a 80's deore triple which has the inner secured by a longer chainring bolt (same thread pitch as the others), but probably 3-4mm longer, spaced by a washer, rather than a jutting-out boss. So if I were to run as a double, the inner face is flush (if you understand my attempt @ explaining).

and to link with another current thread - your soiled chainset had a blemish; todays cosmetic blemish is tomorrows catastrophe with cranks

[Mick F]

Hi Pigman,

The chainsets ARE basically the same, except, as you say, the spiders are different.

The crank profiles are the same, it fits on the same BB and has the same chainline. The rings are the same, except that one bolt-hole is different on the outer to take the different bolt on the crank-arm. But, mechanically and operationally, they are identical.

All Campag bolts are the same length. The Chorus inner bolts are top quality, and the Comp bolts just plain plated steel. Longer bolts MIGHT do the trick, but as the the threads are damaged for the length of the standard bolts, slightly longer ones would only grip a little further down - maybe the same problem as before? Bolts should grip over the whole of their length.

I prefer the Helicoil/boss insert solution.

The scratches are surface cosmetic, not gouges into the alu. The laquer has been scratched a bit, I could polish it out, I suppose. I don't know about anybody else's cranks, but they often get knocked whilst Bike is being pushed up a kerb or step - so what's to worry about an imperfection?

I got a bargain - but perhaps not!!!

[Mick F]

Helicoil don't do a 8mm x 0.75mm thread.

So me and Paul are going to do a repair in the near future. He suggests Monal Metal bosses turned in a lathe and threaded on the outside. Same tread cut into the crank, and then the bosses screwed tightly with thread-lock.

The bosses will have a pilot hole in them and will then be drilled and tapped to the chainring bolt thread.

Each boss will be inserted and taped individually to maintain its correct position. The proceedure will be repeated or each of the 5 positions.

Job done. Wish us luck!

[Bob S]

The only problem I see is drilling and tapping parallel with the spider bore, as it does not look as if you have a machined surface to bolt to. You could may be use an old spindle clamped to a large V Block
Good luck.

[CJ]

Inner chainring screws DO come in different lengths. A lot of chainsets have a thick washer between inner and spider, requiring a longer screw. It looks like this one has an un-threaded bit of boss instead of that washer. Clearly it should have been supplied with long screws, but seems to have been assembled in error with the short screws from another, superficially similar design of Campag crank.

I suggest sending the crank to Chris Bell at Highpath. He should be able to clean up the threads, if necessary make them a bit deeper, and supply longer screws.

[Mick F]

Thanks Bob and CJ.

The Chorus crank's problem is one of poor manufacture, not assembly. Campag used to do longer bolts in the past, and no doubt I could get some sourced, or even get some other make. Either way, it wouldn't work as the good threads further down would be in the same state sooner or later, as there aren't enough of them left now. The threads that have been damaged are completely beyond redemption.

Paul and me had a good chat the other day about holding it central and level. We will experiment!

Of course, I could send the crank off to the experts at Highpath. This will cost. A DIY job will only cost me and Paul our time and £14.50 for the right 8mm x 0.75 tap. We will enjoy the challenge too!

The obvious option is to buy another crank, or dump it and buy the identical Record version:
http://www.ribblecycles.co.uk/productde ... AMPCHAR870

Another, less obvious option is for manufacturers to stop using stupidly fine threads in soft alu alloy! Also to have proper quality control.

But as I said earlier, I got a bargain of a shop soiled chainset. It MAY have been a "second" too.

Watch this space. The story ain't over yet.

[pigman]

The obvious option is to buy another crank, or dump it and buy the identical Record version:

Another, less obvious option is for manufacturers to stop using stupidly fine threads in soft alu alloy! Also to have proper quality control.

But as I said earlier, I got a bargain of a shop soiled chainset. It MAY have been a "second" too.

Rather than dump it, could you (or someone) use it as a double rather than triple? You might have to saw the ears off.

Would buying another Campag solve it? You say Campag dont manufacture long bolts. The short threads/short bolts might be how it is. As long as one doesnt dabble, it would have been ok. I know this isnt really a satisfactory answer, as rings eventually wear and ratios are there to be changed, but might be how its designed (our old friend "renew all, not replace part"). Without re-reading the whole thread, why did you dabble with the small chainring in the first place.

[Mick F]

Hi Pigman,

Why? I stripped it to clean it, and found one loose, then another. When I looked further, the threads were falling out of the bolt holes. Out of the five, only one is ok.

Double? I suppose so, but it wouldn't be ideal and look a bit odd.

Just been looking again:
1. I can confirm that all the bolts are identical, except for the one that goes into the crank arm of course. That is, all five for the inner, and all four for the middle and outer are exactly the same length and design.

2. According to Campag's spares PDF for my C/S, the inner bolts should be FC-RE-102 and the middle and outer bolts should be FC-RE-002 (no mention of length, other than the fact that they are different)

Therefore, as CJ suggests, my chainset was assembled wrongly!
BUT, my other chainset, a Comp, has different inner bolts to the others, but the difference is of material, not size.

And I JUST reckon, that if the 8.5mm long bolts were replaced with 11mm ones, I MIGHT get away with it, as there's POSSIBLY enough thread left deep inside.

PS.
Just looked again at Campag's PDF.
The Record Triple has all the bolts the same - FC-RE-203.
Maybe that's what Ive got. Record bolts, not Chorus.

[pigman]

I stripped it to clean it, and found one loose, then another. When I looked further, the threads were falling out of the bolt holes. Out of the five, only one is ok.

thats the severity of rosedale chimney combined with the brutality of mickF for you.
BTW, how was that climb? Ive only ever seen it once and that was from a car seat and we were going down. Looked like one to be avoided when with bike.