Workshop Stories - Mavic Root Canal

[Johan Bornman]

Workshop Stories ? <?: prefix = st2 ns = "urn:schemas-microsoft-com:office:smarttags" /><?: prefix = st1 ns = "urn:schemas:contacts" />Mavic RootonNAME> Canal.

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A customer friend approached me the other day with a few odd jobs. I had to strip his suspension fork so that he could send it for repainting and, he asked me to take a look at his wheels. ?Give them a good check-over and see if they need truing,? he said.

 

I?m the wheel guy, so what can I say. No? No, not even to Mavic CrossmaxonNAME>. He did say he had a packet of spokes should I need any. I envisaged a large packet but he handed over a plastic bag with one left and one right spoke. Those of you who know Crossmax and Ksyrium wheels will know that this gesture was a bit like asking someone to conduct some F1 testing with just two tyres.

 

Try and say Z-i-r-c-a-l when you're under the influence

 

Mavic wheels with their proprietary aluminium spokes (the French call it Zircal, but try with a French accent as I may, I cannot make it sound even remotely like a-l-u-m-i-n-i-u-m).

 

Aluminium spokes in aluminium nipples in aluminium rims don?t make for good chemistry. Naked aluminium doesn?t like water, or air, or time, or just sitting on a shelf. It responds by corroding and seizing itself onto something with a ferocity that requires at least a hacksaw. The little bit of spoke under the nipple is naked or if not yet with a few turns that removes any coating; it is naked by the time it is screwed in.

 

 

Compare the new spoke on the left with the broken off used spoke and nipple on the right. Note the crusty surface - aluminium oxide.

 

The front wheel was OK but the back one had a wobble. If it was my wheel and since it is a disc brake wheel, I would have left it. However, friends expect and deserve better tolerances than that and I started to true the wheel.  Under normal circumstances this is simple. You tighten the spoke/s on the opposite side of the wobble?s epicentre. The first spoke just-just turned. Second spoke?.wouldn?t budge and without warning, the nipple crown broke off. This is common with aluminium spokes. They freeze onto the nipple and either turn with the nipple, twisting the spoke like a koeksister or, as in this case, the nipple sommer decides to pass over and go to heaven.

 

This is what it is all supposed to look like. The fluted collar is what

broke off.

 

At this point I must warn sensitive readers to switch channels. The rest contains violence, foul language and blood.

 

This is serious. I leave it for a few days and hope it sorts itself out, but as is with these things, it doesn?t. Out comes the side-cutter and twang goes the spoke. Then I file the spoke stump flush with the nipple stump, centre-punch it and start drilling. The objective is to drill out the spoke stump and then insert a stud extractor or similar to turn the nipple out.  The problem is that you cannot drill straight down and do a proper root canal. The hub is in the way of whatever you use to drill with. It?s a question of small holes from as many angles as possible.

 

 

 

Eventually the crater is large enough to insert a stud extractor. I do this and with the first turn it strips out of the soft aluminium. After much deliberating and trying other solutions, I eventually settle on a torx bit that I hammer into the nipple stump. This seems to bite but no, it too strips out. I then decide to go one torx bit bigger and drill the hole a bit more and hammer the next size up bit in there. It bites and slowly the nipple comes out, depositing little mounds of aluminium oxide as it unscrews from its welded grave.

 

A makeshift stud extractor - a Torx bit. Note the neat little pile

of aluminium oxide coming off the nipple as it is forced out.

 

 

Eventually the entire nipple is out.

 

Here's the culprit - the once-seized nipple. Note the course thread

from oxidation damage.

 

Another view of the nipple, in an attempt to show the ruined

surface that was stuck to the rim.

 

 

Once the nipple was extracted, all that remained was the stump of a spoke and some of its former red plastic bearing.

 

I insert the new spoke, tension the spoke by sound right there where the wheel is in the specially-rigged vice and then transfer it to the truing jig. A quarter turn later the wheel is true again.

 

The vestigal of an errant spoke. Note my extra super accurate drilling

(where's that Noddy badge?) that went straight down the spoke shaft.

 

 

The latter half of the operation took 5 minutes, the former, two hours.

 

I consider myself lucky that only two spokes required surgery.

 

 

 

 

 

 

Johan Bornman2009-05-12 11:33:20

[GTRacing]

You are a good friend, and a patient man...

 

Respect.

[dollar]

John - I am confused.

 

You told me that correctly built wheels would never need truing because the spokes would maintain the same tension forever? I mentioned a few things that may change the tension - you shot them down - fair enough - you have built more wheels than I have. How would you have spotted this problem in the early stages? Spoke tension? Pap spokes?

[dollar]

Correction. My appologies Johan.

[straatvark]

 

You are a good friend' date=' and a patient man...

 

Respect.

[/quote']

 

ditto

 

Jig, I would have discussions beteen me and myself with a lot of uittk@k invloved...

 

[Johan Bornman]

John - I am confused.

You told me that correctly built wheels would never need truing because the spokes would maintain the same tension forever? I mentioned a few things that may change the tension - you shot them down - fair enough - you have built more wheels than I have. How would you have spotted this problem in the early stages? Spoke tension? Pap spokes?

 

You don't spot this problem until you have to true the wheel on a Saturday morning before tomorrow's race.

 

They may need truing because they took a knock or, a severe bump on a frozen spoke could make it push the spoke into the nipple, never to return to its original position. I cannot remember if the original wobble was due to a slack or tight spoke, I did the operation some weeks back.

 

You must remember that these are not standard wheels and they have many quirks that make them react different from other wheels.

 

 

 

 

 

 

 

 

[Cassie]

Personally, I've NEVER had any such troubles with a nipple....

 

More seriously, what can you suggest to combat Alu oxidation? Should this be part of regular maintenance?

 

I would have thought that different combinations of metals would be more problematic - they call it something like galvanic corrosion (when electrons flow from one metal to another, causing the one to corrode). did not expect something like this on pure Alu parts? or is this just plain old "rusting" of Alu...

 

[dollar]

Ok. Fair enough. Interesting thread. Thanks.

[SwissVan]

Personally' date=' I've NEVER had any such troubles with a nipple....

 

More seriously, what can you suggest to combat Alu oxidation? Should this be part of regular maintenance?

 

I would have thought that different combinations of metals would be more problematic - they call it something like galvanic corrosion (when electrons flow from one metal to another, causing the one to corrode). did not expect something like this on pure Alu parts? or is this just plain old "rusting" of Alu...

 

[/quote']

 

Nice story JB  brought back some memories non of which I hope to experience again.

 

Cassie ? Yes aluminum definetly ?rusts? or oxidizes producing the whitish powdery by product which usually can only be removed by a polishing or cleaning action applied to the surface that is ?rusting?.

Both of which would not be practical unless you feel like performing JB?s root canal treatment process on a regular basis?

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There are various industrial products (other than anodizing, which wont work effectively on threaded parts) which might have a protective effect and pro long the useful life if applied at manufacturer or when you buy new wheels.

IMO it would be better to stick with a wheel that uses a more resistant material such as stainless steel or composites if you want to save weight.

 

 

[Underachiever]

Johan, I envy your patience.

 

Seems that I was a wise man when I sold my Mavic Ksyrium SSC's for a Campag Eurus set a few years back.

 

Like your pics Johan, what macro lens do you use?

 

and........

 

I see a reference to heaven, converting?

[Johan Bornman]

 

Like your pics Johan' date=' what macro lens do you use?

 

 

Those pictures were taken with a Nikon Coolpix 4500 - about 6 years old. Has the best macro lens I'm yet to see on a low-end camera. I've fitted it with a "ring flash" but it's not really a flash, just a circle of LEDs.

 

When anyone gaans on about Megapixles, I pull out my trusty Nikon and do a shootout to prove that it's not about the megapixels but about the lens. This camera only has 4 Megapixels.

 

 

I see a reference to heaven, converting?

 

No need to convert, when I operate on wheels I am in heaven.

 

 

 

 

[Jadon]

Regarding your problem of not fitting a drill into the space betwen the rim and the hub:  don't know how often you do this, but Festool have an attachment for one of their drills that put the drive through 90 degrees, and another the off-sets the drive. Check it out here: http://www.festool.co.za/mediandoweb/index.cfm?sLanguage=English&ID_O_TREE_GROUP=3593&PARENT=1569&AKTIVPROD=1

[Johan Bornman]

Regarding your problem of not fitting a drill into the space betwen the rim and the hub:  don't know how often you do this' date=' but Festool have an attachment for one of their drills that put the drive through 90 degrees, and another the off-sets the drive. Check it out here: http://www.festool.co.za/mediandoweb/index.cfm?sLanguage=English&ID_O_TREE_GROUP=3593&PARENT=1569&AKTIVPROD=1[/quote']

 

Thanks for the link.

 

I've done this twice now, so time for a special tool, I think. I've deserved it. Luckily for me, up to now I've been doing something similar on Ksyriums but only to replace cracked rims. Then it's easy, cut the rim to pieces and hook the spoke out of the hub and then work on that section only...if I think the spoke can be saved. Often not, then it's cut and replace.

 

 

I have an 90 degree thingy similar to that but I find that it is clumsy and I don't have the control of directly getting in there. What I really need is an offset Dremel with an abrasive bit. It is just so difficult to keep the drill centered so that it doesn't depart from the spoke and starts eroding the rim itself.

 

It is a little bit like dentistry.

 

 

[SwissVan]

 

 

I have an 90 degree thingy similar to that but I find that it is clumsy and I don't have the control of directly getting in there. What I really need is an offset Dremel with an abrasive bit. It is just so difficult to keep the drill centered so that it doesn't depart from the spoke and starts eroding the rim itself.

 

It is a little bit like dentistry.

 

 

 

http://www.bosch-pt.co.za/boptocs2-za/Product.jsp?country=ZA&lang=en&division=gw&ccat_id=101359&object_id=5782

 

Might be to expensive VS the amount you need to use it, but an angle drill is perfect for those hard to reach places.

 

 

[PhilipV]

 

 

Like your pics Johan' date=' what macro lens do you use?

 

 

Those pictures were taken with a Nikon Coolpix 4500 - about 6 years old. Has the best macro lens I'm yet to see on a low-end camera. I've fitted it with a "ring flash" but it's not really a flash, just a circle of LEDs.

 

When anyone gaans on about Megapixles, I pull out my trusty Nikon and do a shootout to prove that it's not about the megapixels but about the lens. This camera only has 4 Megapixels.

 

 

I see a reference to heaven, converting?

 

No need to convert, when I operate on wheels I am in heaven.

 

 

 

 

 

Amen to that!

Do you mind putting up a photo of your diy led ringflash please?

Sounds interesting...

 

[Johan Bornman]

No the "Flash" is not DIY but pure Nikon.

 

Here's a pic of the camera and the flash.

 

 

And here is the flash on its own. It works of one of those expensive fat 3V Lithium batteries and give off a reasonable amout of light. It would be better if I could find a copy stand of sorts since most of those exposures are taken at 1/4 of a second....1/25th if I'm lucky. I've learnt, like a marksman, to control my breathing and heartbeat when working in handheld macro mode.