Saturday, December 12, 2009

Rivet nut replacement

When I attached my water bottle cage to the seat tube of my new bike I failed to notice I was using aluminum bolts. That bit of carelessness resulted in breaking off the first of the 5mm bolts I tightened.

Normally this a simple fix using a Craftsman Drill Out Micro Power Extractor to remove the remains of the bolt, but it was not going to be that easy. When attempting to extract the bolt the rivet nut started spinning in the frame. The combination of spinning rivet nut with a broken bolt stuck in it left me no choice but removal.

After drilling out and removing the rivet nut's remains from the frame, I purchased a Marson zinc plated 5 mm Riv-nut from Bikeman ( http://www.bikeman.com ) for $2.99 USD. Actually I bought two just in case I spoiled one on my first installation attempt. This turned out to be a good investment.

I didn't want to purchase a rivet nut tool, so after doing some searching I found instructions on the Park Tool website ( http://www.parktool.com/repair/readhowto.asp?id=147 ) on tightening up water bottle fittings. While the instructions and make-shift tool used are for just tightening a loose rivet nut, I decided to take the chance they would also work for installing a new one.

My makeshift tool consisted of an adjustable spanner as the spacer, a cheap steel front skewer, and spare Campy front hub. The picture to the right shows the setup with Riv-nut in place. My first attempt to install the Riv-nut yielded a couple of problems. The first is the thickness of the adjustable spanner's jaws are tapered. This, in effect, creates a wedge between the skewer and the axle nut resulting the bending of the skewer when tightened. The second problem is the axle ends are not flat but beveled distorting the Riv-net's face as pressure is applied . The result was bad enough that I decided to remove the Riv-nut an start over.

On my second attempt pictured on the right, I corrected the shortcomings of my makeshift tool by substituting an open end wrench with uniform thickness that would still be me a good leverage. I also installed a washer on the skewer between the axle end and Riv-nut to provide a large flat surface.

Admittedly it took a fair amount of effort using this setup to install the Riv-nut since the skewer doesn't provide a lot of leverage. With each close of the skewer's lever I had to screw the skewer a little bit further into the Riv-nut and repeat. After several iterations of this, I was able to compress the Riv-nut sufficiently to secure it into the frame.

After thoughts... I think the technique I used is probably not a good solution for installing a new rivet nut. The hub or even just the axle from it is a bit awkward to use and requires a lot of finger strength to set the rivet nut. Probably a better low-cost alternative to a proper rivet nut tool would be a strong steel 5 mm x 20 mm bolt, a mating steel nut, and some washers. The idea would be the nut, bolt and washer assembly would be screwed into the rivet nut and with the bolt held in place while the nut is backed off thereby compressing the rivet nut. This would give more control and require much less effort.

Lastly, while writing this entry I found a source for a very basic rivet nut tool for under $30 USD from Rivetnuttool.com ( http://www.rivetnuttool.com/ ). The tool itself looks simple and easy to operate within the confines of a bike frame so I am considering purchasing one.