Monday, 24 September 2012

Project "Tandem BMX bike"

 More than nine different bikes were used as parts donors to make this one of a kind BMX.

Built entirely from scrap bikes left on the side of the road for the annual "hard waste" collection, this tandem project has cost less than $10.

Initially put together about two years ago, this project was servicable but scruffy and unfinished. The last "hard waste" in August saw some very tidy bikes put out for scrap. Being out on the scavenge for bits for another project, it was too tempting to collect some bikes with useful parts to upgrade the tandem.

Some decals left over from a paint job 16 years ago finished the look off quite nicely.

 This picture shows the almost new wheel (one of a pair) that I got last month. The rear brake has now been installed and tabs welded on for the gear change cable. The cable was run in and connected after this photo was snapped, as the light was starting to fade.

 Front forks were replaced, again from the spoils of the last "hard waste" as they had better brakes fitted.

My girls chose the colour from a limited palate made up of "mistinted" paints bought cheaply. It is brush painted in enamel house paint.

A few hours with a paint brush and the job looks a lot tidier. I got a little carried away with the pinstriping!

This photo, although out of focus, shows where the seat post from another bike was inverted and stitched in between the two 20" frames to give the rear rider (stoker) enough room. The join was then bogged over and smoothed. The goose neck for the rear handle bars has been turned around to give the "captain" enough room on the seat.

Finishing touches like the reflecters, handle grips, crash pads, seats and coloured pedals all came in the last batch of bikes pilfoured for parts.

One of the toughest things to sort out was the chain set up. Two sprockets were welded together on the rear crank. Enough space had to be left for the counter rotating chains at the back of the sprockets. The final drive sprocket is welded on the outside and is a smaller diameter to reduce the chances of anything catching between the two. Originally both bikes were "coaster wheel" brake (back pedal for brakes); not a good idea for a tandem. I couldn't find a freewheeling hubbed wheel, so I stretched the rear forks out a little and fitted a six speed wheel. This has some advantages for riding, but meant more work to set up.
 Tensioning the front chain was also a challenge. Ideally I only wanted a single idler sprocket. Most tandems use an adjustable rigid mount idler sprocket. It was far easier to set up a deraileur to achieve the tension and I like the idea of the spring action. It seems safer for kids some how.

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