Installing a Velo Orange Porteur Chain Case on a Big Dummy

September 20, 2009

It was tedious and fiddly to get it on right, but I am happy now.
The rest of this post contains some large photos.

Update: see this annotated photo for the latest state of the chaincase; I did some additional modifications.If you go looking for instructions online, you won’t find much. The product page says it “works with modern Sugino Cranks”, and it does, but just barely. My crankset is a Sugino RD2, with a 38 tooth chainring, and a track (103mm?) bottom bracket.

First, the results:


The chaincase mounts on two pegs that strap to the seat and down tubes, and a sort of U-clamp that grabs the chainstay, if there is one.



My plan was to put the nuts on the outside; that might not be quite as pretty, but it was clear that this was going to need fiddling and adjusting, and I have a new chain and chainring in the mail (the old ones are badly worn), so all in all this seemed like the best plan.

The main problem is that the clearance between crankset and chaincase is very small, perhaps a millimeter at best. I spent about a day dry-fitting, not sure if it would work. I had to do the final fitting with the bike laid over sideways and propped up, so I could rotate the pedals freely.

A Big Dummy presents two additional problems, one minor, one tricky. The minor problem is that the down tube is really large, and the supplied mounting strap simply does not fit. Fortunately, I had some stainless steel of the appropriate gauge hanging around, so I cut myself a new strap.

The tricky problem is that there is no chain stay, so the clamp provided with the chain case does not work. The tube has a weird oval section, and is large, so it’s tricky. I started with a trick that my brother told me, which is to make the clamp you need from Fimo or Sculpey:


This worked well enough, but I decided that I could use the Sculpey as a guide to carving (with a Dremel) a piece of PVC pipe:



It’s necessary to drill holes in the chain guard to mount it, so I got as close as I could with the dry fit, and marked marked the chain case with pencil.


Once it was rough-mounted, I used an allen-wrench in the gap between the crank web and the crank arm to be sure it was centered, and tinkered with the mounts to get it right.


Because I wasn’t using the chain stay clamp, I had two spare nuts, so I doubled up on the mounting clamps, mostly because a nut is a smoother and less snaggy surface than a threaded end. I could also Dremel the excess threads off, but that would make it harder to work on in the future, so I decided to start like this and see how things went.


You’ll notice that the rod (below) looks like it is not perpendicular to the centerline of the bicycle; this is intentional, for whatever reason (skinny track BB, probably) if it is perpindicular, it is too long.


I put two holes in the rear part of the chain case above and below the top edge of the PVC; the idea was to pull it tight with zip ties so it could not rotate down. I pulled it tight, checked the clearances, and it was too thick, removed a few millimeters with a power sander, until it was just right.



And it works. I took it for a ride of a few miles, bumps and all, in jeans with no pants clip, and they did not snag (I was a little worried about the mounts) and it did not rub.

See also, more chain case upgrades, I added a pants ramp and a splash shield on the off side (as of this writing, late December 2010, the splash shield is overly cracked and removed, but I plan to replace it).

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