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Old 01-14-20, 09:53 PM
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Join Date: Jun 2010
Location: Medford MA
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Bikes: Ron Cooper touring, 1959 Jack Taylor 650b ladyback touring tandem, Vitus 979, Joe Bell painted Claud Butler Dalesman, Colin Laing curved tube tandem, heavily-Dilberted 1982 Trek 6xx, René Herse tandem

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Rivnut Rinko

I did the thing I said I would, and reinvented the wheel. Or, rather, the fender. Close enough to the wheel, both literally and figuratively. Jokes aside, I think using rivnuts and removing the whole fender is a viable system. Here’s what I did.

First, I brazed a nice flat plate under the seatstay bridge of the frame This has holes fore and aft of the bridge.

Then I put two stainless M5 rivnuts in the fender. You can see I’ve got a nice stainless reinforcement plate on the inside, peened to match the curve of the fender. The rivnuts were actually pretty hard to “set”, probably because they are stainless. I couldn’t do it with a bolt and a nut, even a good quality, well-lubricated bolt and nut. I rounded off the nut and bent the bolt trying. I ended up setting the rivnuts on the arbor press, but it would be possible to do in the jaws of a vise as well.

Second, I put a rivnut in the bottom-front of the fender, along with an aluminum reinforcement plate.

The bike looks like this with fenders. The fenderlines are perfect as it stands, and the rear wheel is all the way forward in the dropouts. It has room to slide farther forward and come out with the tire fully inflated and the fender installed!

And like this rinko’d.

I also TIG welded a reinforcement plate to the rivnut flanges on the top of the fender. While it looks pretty, I do not recommend doing this. I cracked one of the rivnuts in the process and had to re-weld part of it, and I wonder how long it will last.

My observations about installing the rivnuts are mainly that the hole in the fender must be exactly the right size, or else the rivnut will get set asymmetrically and screw things up, and that setting the stainless rivnuts requires great force. Also, you must pay attention to the maximum allowed thickness for the rivnut. If you try to put a rivnut through too many layers, it will just end up a big mess. Other than that, they are straightforward, and this is feasible for the home shop user.

The bolts have leather washers on them, so they are (lightly) retained when the fender is removed. The lower one uses some home-made thick washers that are significantly better at retaining the bolt, so maybe I will home-make some more for the upper bolts. I also think I need to make the front hole in the upper mounting plate a little slotted so the bolt can slide backward a little as it is undone. This will make rinko a little easier.

Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.

Last edited by scarlson; 01-14-20 at 10:09 PM.
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