Sunday, September 1, 2013

If items of horror can make a man laugh

Yesterday I went to Sirkus Caliba with my youngest daughter, to see the show and enjoy the evening. This circus group visits the nearby football field each year at the end of summer, but often we have had some other program and haven't been able to go. The show had changed quite a lot, and it wasn't at all bad, taking almost two hours with a 15-minute break in the middle.

CJ Gordon commented my troubles with the bicycle, suggesting that if this is a matter of back wheel going out of true, it would be easy to learn the repair skills. Well, I'm not so great with fixing mechanical things, and then this doesn't seem to be a straightforward problem. Here is what I wrote in the comments:

It is not really the wheel going out of true, it is the spokes breaking near the rim of the wheel, one after another.

I have a gear hub in the back wheel, Nexus 8, so-called red-band version, and I had the old gear hub replaced after 15 000 km, when it had worn out. At the same time the rim, spokes, etc. were replaced with new ones.

But then, spokes started breaking so that the screw thread part stayed in the screw at the rim; the spokes break at the place where the thread stops.

I have been thinking that perhaps the wheel is not put together properly, but I'm not sure what would be the right "pattern" for a gear hub. The gear hub is bigger than an ordinary one, and so the spokes are more angled when they start from the rim, and thus there is sideways torsion which must be a reason for the breaking.

I borrowed from the library Bike repair manual by Chris Sidwells (in a Finnish translation), which gave some instructions on how one should approach truing wheels, but still I have no idea what is the problem here.

(Posting title is from the poem In the Theatre by Dannie Abse.)


Markus said...

First of all the images: Convincing, and supporting the truth that sensor size matters much less than mastery of the tool.

Re. the bike: I've been bicycling 50.000 km or more and never had problems with spokes breaking near the rim, alway near the hub. Keep in mind however that I am fairly lightweighted, about 70kg at that time.

Three things come to mind: it could be a faulty batch of spokes, or a problem when mounting them. If the spokes are a wee bit too long and the thread vanishes completely in the spoke nipple, force might be exerted on a already weak part of the spoke, and the torsion when mounting them might cause damage, which is at first hidden. The fact that the spoke breaks within the nipple might hint to such a problem. And, not to forget, it could be a bad sort of nipples, cutting into the spoke material when mounting them. If you do that by hand, you can feel it, but in most workshops powerful machines are used for that task. Anyhow, if you unmount an unbroken spoke, you might get a hint of what is causing this problem.

If I would encounter such a problem, I would most probably go to another workshop, maybe of the cross-country bike sektor, where they have a lot of experience with high stress on bicycle parts.

Juha Haataja said...

Thanks, Markus!

I think you are right about the reason for the problems with the spokes. If it happens again, I'll have a look at a spoke to see how it is fitted. Going to another workshop to get a second opinion, that would be worthwhile for sure.

cj gordon said...

You have an interesting problem with that back wheel. Beyond my understanding as I've never had an internal gear hub and after reading about yours I'll make sure I never do.I weigh 220 lbs and have not had a spoke break in all my 40 years of riding but have had too keep a few wheels in true with my limited skills.Hope you manage to get this solved with a minimum cash outlay.Very nice set of photos.

Juha Haataja said...

Well, I hope the problems are now fixed. And the bicycle repair shop said that if the problems appear again they will fix the wheel under guarantee.