mercredi 29 juillet 2015

Rohloff sprocket yields to custom chain whip

from the down-the-vet's department 

So I ordered a new sprocket for the Rohloff, and the special tool to remove the old one, from Bike24. This admirably clear instructional video had given me confidence that replacing the sprocket would be a straightforward job:

The chain whip tool I've long owned is about 30cm long, but when I tried it as recommended in the video, it was clear that it wasn't going to budge the sprocket. I began to develop a serious case of chain whip envy: that man's in the video is simply enormous! Also, I didn't have a 24mm spanner, and an adjustable spanner just isn't as good to use. So, inspired by this video:

I decided to make my own chain whip tool (and score myself a 24mm spanner).

Tracking down the steel flat bar required to make the chain whip tool was the biggest part of the job. A physical copy of Yellow Pages turned out to be more useful than my online searches, which just tended to pull up endless cheesy business directory sites. Anyway, I can highly recommend Blanchard Matériels Industriels (SARL) in Vertou, who were very helpful, even though 45cm of 4 x 25mm mild steel flat bar for €2,65 may not be the biggest order they've ever fulfilled.

Then it was up to Ouest Injection for the correct spanner (the Kraftwerk brand, pleasingly), and home in time for tea! The sprocket had been marinading in WD40 all day, but even with the new longer chain whip it wouldn't budge, despite applying hideous amounts of force. I decided to try heating the sprocket with the Camping Gaz stove. The ensuing WD40 fireball certainly impressed my admiring family audience. Finally, I dipped the sprocket in a bucket of boiling water (holding the wheel horizontally), and at last it yielded. So I have now fitted the new sprocket. You can see the old one, seriously worn, with two missing teeth, lying on the red cloth in this pic:

From top to bottom: Rohloff-hubbed wheel with new 16-tooth sprocket fitted, new 45cm chain whip, old 30cm chain whip, new 24mm key, old adjustable spanner, old sprocket, grease, link extractor.

Oh, and I agree with the commenter below the "make your own chain whip" video that it is crazy to use M3 bolts to secure the short lengths of chain to your flat bar. Using the original chain rivets works perfectly well. According to my vernier, the chain rivets are 3.84mm in diameter, so holes drilled to 4mm diameter in the flat bar were just fine. After a false start placing the holes slightly too far from the edge of the bar to accept the chain links easily, I started over, and hid the bodged holes under the handle tape. You can't use a rivet extractor to resite the rivets (the bar is in the way), but a few careful taps with the ballpeen hammer slid them into place excellently well.

Aucun commentaire:

Enregistrer un commentaire