If it was my bike and considering it's so out of line and looks like it could do with a proper clean and repaint..... I would strip it completely and jig it to comply with the frame dimensions given in the 'Technical section' under 'Wheel building and frame dimensions'.
I could MIG weld it myself, but would rather give it to my professional welder guy to TIG weld.
No doubt the 'oily rag patina brigade' will shoot me down in flames.....Bovvered??
It is brazed, the connection tube has a sort of trumpet formed on the ends which suits the frametubes. I would blast it clean and braze it on the same spot again. From the breakage you can clearly see how its position was.
But if you decide to weld it indeed remove all the braze as it will melt into the weld and weakens it badly.
Hi i can confirm what Michiel has said, i had to do this repair only last week on my frame. If you want to retain old finish don't use a regular blow torch use oxyacetylene the flame is finer and and heat dissipation less so the surface repair is smaller. A good clean with a wire wheel and a good quality flux should give a nice clean joint also, if you don't have access to a blaster.
regards Grahame
I don't think that the wear on the crank case boss is due to the frame out of alignment.
It looks like the chain has been rubbing on the boss because of a lack of the spacer between the cush drive sleeve and the bearing. Notice the wear ring around the inside diameter of the case.
If you hae a crack in one place then common sense says to blast the entire frame and check every where for more cracks .
Stuff the Original patina brigade ( od which I am one ) they are not the ones who are liable to be doing a belly flop on the gravel when the frame brakes
Get it jiged up and welded by a professional way with a cheque & get a receipt.
The £ 5 you save for a cash job would not even cover your wife's bus fares to see you in hospital
Many thanks for the input and as ever comprehensive
The frame will be getting a complete makeover in terms of finish, the project is for running on a salt lake so I'd always intended that. Fining the break just means I need to consider that as an integral part of blasting and coating.
Before I do that though I'll sort out, or try to sort out things that are currently wrong, missing, misaligned. Having pondered a little more I think the skew look is from the positioning of the brake anchor, which I'm pretty certain from squinting at my photos is positioned outside of the lower chainstay and I think this should be inside?
I'll make some better measurements at the weekend. In the meantime, does anyone know the correct sizing for the front distance piece, 66-4183? I've got what I think are the correct sizes below for the other parts of this, but I can't locate details for 66-4183.
@Matty - I think you're right about the about the engine sprocket and the crankcase, even with the 16T sidecar sprocket the spacing should push it out enough, the top run will be the one this bites if it's too close because that's the part of the sprocket where the chain pulls in to drive. When I looked for the locking washer (there wasn't one) before attempting to undo the sprocket nut there was a gap between the nut and the cush drive bearing (65-2539) which I think indicates that the whole thing hadn't been spaced correctly. I'll just note this on the re-build work as I'll have to correctly align the sprockets to minimise all my frictional losses anyway!
BUT! If you fit a cush drive that doesn't have the built in spacer and omit the loose spacer. I think it's near impossible to turn the engine over. Ron
I'll check...remember the nut wasn't tight, so that may have helped the engine to still turnover...it doesn't look as if it was really ever run - even starting a little would take the shine of that +20thou piston...
Something else that might not have helped is that that I think the chainlink had the link facing inwards, because when I looked for the link I didn't see it, but as the gearbox as not bolted in place and after I'd undone the engine shaft shock absorber I could remove the primary chain in one. I'll take a look at the chain to see if the link has bits of ally in it, and the rest.
I'm going to focus on frame and forks for a while though; can't get too distracted by the exciting parts like engines and gearboxes just yet
Nothing would surprise me about this bike! It will be a joy when done, now it's a little like a crime scene, but I need to brush up on my forensics skills
This is how I checked and straightened a frame. I Clamped a straight edge to the front and saddle tubes. I could then determine the centre position of the rear spindle and tweak the frame accordingly. Ron
No heat needed Patrick. Each side of the back end of an M20 frame will bend cold as long as you can hold the main frame somehow. You can see how I held it. I remember another forum member held his frame in the fork of an Apple tree Ron
That's brilliant! If I find mine isn't true then I'll follow this approach. I didn't get to work on her this weekend, got sidetracked with IT support at home...which has consumed all of Sunday, still I'm sure I'm more educated now.
Anyway, next weekend I'll check, measure, re-check, re-measure and only then plan some well aimed brute force.
Looking at your first photo, the short strut on the top of the rear frame, just below the seat looks as if it has been cut and re-welded, or re-enforced in some way. The second photo shows a hole drilled through the same strut.
When I straightened my frame, I cut this strut so that I could straighten each half separately, first using the "tree" method then using a vice with half round anvils, all cold. When everything was straight, I re-assembled and found a twist in the frame. To fix this, I bolted it to my work bench and pulled it straight using square tube and threaded rod, then heated the stress points with oxi-acetylene. On cooling it remained straight. One should use heat reservedly, consider carefully where to apply heat, use the correct size nozzle and avoid butane as it has not got enough heat.
The two halves of the short strut then lined up. I fitted a spool and brazed it up. I do not have a hole in the strut and fix the mudguard using a saddle.
All dimensions are now within a millimeter or two of the frame drawing.
Most important is that the lugs holding the rear axle are parallel and horizontal to each other and in-line with the frame. I also used heat to correct this.
Hi Peter. The first picture I posted is actually after I'd straightened the frame and welded up that hole. I've also used a correct saddle clamp. Here is that frame under construction. I've done over 5000 miles on it since I built it and it handles very well. Ron
Here is my rear frame gauge. I'll ask Henk to post it into the technical page. Ron
PS I just noticed that the threads are nearly 1/16" longer than I quoted, hence the discrepancy in the added total, but it was early However the threads can be any length!
Yes Hans Robb actually made and gave me this gauge. I'm just passing on the dimensions for anyone who wants to make one. I didn't notice anything about it in technical, but Henk is looking into it. Ron
Hi Chaps,
I have made a frame gauge to Ron's dimensions and measured my rear frame, only 3mm off, not bad considering the state of it! However there is more to this than meets the eye, the diameter of the down tube is 38.11mm and the seat down tube is 34.81mm a difference of 3.3mm. As all the measurements are being taken from the tube centres the straight edge is not running parallel to the centres, I would suggest using a 1.6mm spacer on the rear tube in order to achieve parallelism.
Hope this all makes sense and helps.
Cheers
Jim