Howdy I have a set of somewhat sad M20 girders- the legs without the boss for the speedo cable are bent inwards towards the center of the front hub approximately 10mm.

I'm unable to detect any sign of cracking, breaking or damage in the middle casting(the bend is essentially in the tubing just below the middle casting, it's a slow gentle bend, no crushing of the tubing is evident, and the bend was completely overlooked by the eye until i sat them on the bench and put a wheel in them) Essentially I am wondering how feasible a repair might be, and if anyone else has any experience performing a similar job?

Currently I'm contemplating a replica of this jig, which was built to test the trueness of a set of '38 Triumph girders at the Brooklands museum- essentially the rods going through the top castings and axle drop-outs were laid out to replicate the factory dimensions, so as the jig would essentially identify if any two or more aspects of the critical dimensions were out of parallel.

I could replicate this jig easily enough, but instead have a large threaded rod in situ of the axle, and turn up a large flanged collar, pushed by a nut from the inside of the lower leg at the axle drop out, to push the leg outwards from the center line of the forks, whilst heating the leg from the middle casting down with my Oxy Acetylene torch. Thoughts?


-Nick

Does anyone have any factory drawings of the M20 girders detailing dimensions? I know the Tech section has a few measurements kindly listed by Ian HERE, but no drawings.

Hi All
Nick the Standards Manual (off Henks disc) has the frame and forks with measurements in fig 1 page 41. Mine were bent about 50 mm to the left and I made up some soft wood jaws for my vice and used a crowbar (6ft) to cold move each leg back true. Drew straight parallel lines on the garage floor and used squares to check the alignment. Had to bend the plates the axle fits into as the bending was sort of trapezoidal. Also kept refitting them into the frame with long threaded rods through pivots and head to make sure the wheel rim was centered and square with the front down tube. The bike was a bugger to ride with the front so out of alignment (I last rode it in the late 60s when the mag failed!!!! hope to be back on the road soon)
All the best
Doug W

email (option): watsond@xnet.co.nz

This was my thread on the subject and how I've managed to straighten a couple of sets.
Note that the left leg is splayed further that the right to accommodate the speedo drive.

http://pub37.bravenet.com/forum/static/show.php?usernum=3155626639&frmid=16&msgid=1356725&cmd=show

Also the diagram from the 'standards book' Ron

email (option): ronpier@talk21.com

thanks Ron, thanks Doug. Much appreciated!

tomorrow i'll have the garden hose run a stream of water across the middle casting whilst i heat the RHS legs and use the nuts on the lower threaded rod in situ of the axle to push the leg back into place, i'm concerned about sweating out the braze at the middle casting but this is actually holding everything pretty darn rigid. Will report back with how I go.

I didn't find a need for any heat to push or pull the legs sideways. Too much heat to make the tube soft could make it easier for the tube to distort. I would guess that if you had to move a leg over say 1/2" you would have to screw the nuts about 1" to allow for spring back. Trial an error of course, but I'd do it cold. I've also straightened M20 rear frames cold. I once had an Ariel W/NG frame profesionally straightend by a firm with a jig, who straightened it cold with hydraulic rams. (Didn't even crack the paint!) Ron

email (option): ronpier@talk21.com