Are their any sensible/useful frame modifications that can be made to a 1972 Commando roadster (inc. swing arm)? I have it in bits and it seems a waste not to do anything that might improve it while in this state. Also, is there a good paint shop for the frame in the S.E. (I'm in Eastbourne)?
Guy First make sure its st…
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I was wondering why, when…
I was wondering why, when I went to connect the rear shocks to the swing arm on my '69 Roadster, I always had to push the swing arm up and compress one shock a bit to get the bolt in the eye of the second shock. mmmm...I'm thinking bent swing arm.
I pulled the swing arm out and laid it up on the work bench. I slid a length of 1/4" roundbar about a foot & half long through the pivot point and another through the axle slots. It's extremely handy to ensure the lengths of round bar are straight.....!!! Eyed the swing arm from one end aligning both round bars. The centre line of the pivot end should be exactly in the same plane as the centreline of the axle. So, if the swing arm is straight and the pivot point and the axle slots are in the same plane, one 1/4" rod will disappear completely behind the front 1/4" rod along the line of sight and all will be hunky dory. The fact the 1/4" rod lays at the bottom of axle slot and the pivot journal makes no difference, they should still be in the same plane. I'm sure we will get scientific geometrical arguments here splitting hairs over fractions of a mm, but if your swing arm is bent it will be bent big, not little. With the extension of the 1/4" rod 9 or so inches out each side of the swing arm it will be very clear and obvious if the swing arm is bent, because instead of one rod disappearing behind the other, they will form a cross. This test can be done easily on any swing arm.
Norton swing arms are very weak. I simply clamped my swing arm in a big vice and stuck a piece of timber through the arms and bent the thing back into shape. It was easy. Checked it again with the rods, put it back on the bike and both shocks easily bolted up together without pushing or shoving, the rear wheel looked better from behind and the bike handled that little bit better.
My point is, it is very easy and simple to check the straightness of the swing arm, you don't particularly need a flat surface and it's easy to straighten it with out gollups of brilliant science, not to mention you will discover how inherently weak the swing arms are!!!!!
Have fun
Bob
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Guy
First make sure its straight! Then if you want it to track as wellas possible without going overboard check the front and rear ISO's for same offset both sides. Did mine and it made a hell of a difference (no more speed weave). Mine was 060" more on front (0.31" and 0.25")twisting whole engine and rear wheel assy to the left. Yours may be OK but it's worth a simple check. While you are at it get the tube ends squared. That helps with even gaps when shimming. Check the frame tabs hole centres (ISO mounts) are same distance front to rear. On the S/A it is worth checking it is straight. Usually they will have bent a little over the years. Sit the pin in the bushes and on blocks on a good level surface and see which side touches first. If it's not too bad you can file out the axle slots to get it parallel with pin but then you have to assemble to wheel & axlespecially if you do that. Some brace the arms similar to 850, seems to be worthwhile. Finally you could look into welding nuts to the S/A tube, drilling through and adding short bolts to retain the pin more securely. Replacement pins have flats for Mk3 cotters and the bolts bear on these. Also worth looking at the centre stand holes and welding up/redrilling in case they are oversize through wear. Same for the sidestand.
Can't answer on paint local to you. I had mine powdered by Maldon shotblasters and powder coaters in Essex.