Saturday, May 24, 2014

Long wheelbase bike: construction

It has rained all day. I have welded all day. Here are the useful 'structions to make a bottom bracket for the LWB bike. (I entertain the vanity someone will want to know.) The photos can tell the story. All you ever need to know is that the front derailleur mech needs a post at 61 degrees from the chainline. - At least, I hope it does. -

First, select a donor bike for the BB shell. These days I check that the left and right hand cups are parallel. Once upon a time this was guaranteed, but in recent times a number of bike frames have come off the hooks in the rafters where one or other thread has lost interest in parallelism, and even brutal force used on a plastic-shelled sealed BB axle has failed. Such bikes attract the attention of the hacksaw and the BB shell is put to one side as Whucked. (Whucked: a word understood only by New Zealanders. I offer no explanation. In polite circles people say 'munted'.)

Yet another bike that I was given, no doubt because it was so heavy.

This particular bike had, on dissection, a seatpost long enough to be a hazard to aircraft. I was most surprised. It may have contributed to the vast mass of the bike when it was given to me. Luckily it also yielded a useful length of 38mm tube for something else, and a seat post clamp that is about to be repurposed. If I ain't going to have an adjustable seat I shall (probably) need an adjustable BB. Two other bikes also had their seatpost clamps filched to this end.
 Donor seatpost clamp. You Dremel through the tack-welds to free it.

 The support plates are 3mm thick

 Brave attempt to align support clamps. Too fiddly; it didn't work. 

 Cruder, but more successful

 The idea is to ensure the BB ends up square to the bike.

 Here we are, welding commenced

 Favourite welding clamp: the inner-tube strip

 Held in line on a spare bit of tube

 Ends welded on, and now ready to attach.

The crossbar will need means to pivot the handlebar. I snipped a piece of head-tube-and-crossbar off another donor bike, cut the head tube short, machined the cut end square in the lathe, and welded it back into the incipient crossbar.

 A beautiful bit of welding. - Shut up, Mr. Knight.

And on with the BB,the seatpost clamp wedged open with bits of wood. (Applewood, natch.)

We shall see if it rains all day tomorrow.

Labels: ,


Post a Comment

Subscribe to Post Comments [Atom]

<< Home