Hello,
I have a 1969 Thunderbolt with the bobbin bearing type swinging arm. During its earlier life this bike was mercilessly ridden with a 750 conversion. This combined with two adults on the bike, two children in a sidecar along with camping gear has resulted in a twist that shows itself as more wear on one edge of the tyre (exaggerated lean angle) and wear on one side of the sprocket as the chain has to twist ever so slightly as it pulls the sprocket around.
What is the best way to straighten it?
Dave.
I had a nasty twist in the rear section of the M20 frame. I put a bar across the rear wheel spinle bracket and used system of ratchet straps to pull the frame until the spindle was aligned with the frame cross members. I then applied heat with an oxy-acetyline torch to the section of the frame looked crooked until it was red. I then let it cool and removed the ratchet straps.
If you can find something substantial to attach the swing arm to you could try the same.
Hi Dean,
Did you treat each side separately? On my one both sides are twisted by the same small amount so it would be necessary to twist them back separately. I will probably try heat and twist or twist and heat and if that does not work then a replacement will have to be found. If only covering small mileage then it probably would not matter but over longer distances the wear on the chain and sprockets is not really acceptable.
I may try a cold twist first.
Dave.
remember to keep the spindles in to keep in line when heat applied
Dave
I only had one torch so did each side separately. To clarify, I pulled them into position cold and then applied the heat. This overcame the natutal springiness of the steel and reduced any stresses induced by the cold twist. These stresses probably aren't that great though given the small bend of your swing arm so cold might be fine although you'll have to watch the orignal welds are OK.
Good luck.
Thanks Dean,
I think the A65 arms are not as strong as the A10 and being longer should twist quite easily. This more 'weight saving' design is probably why the twist is there in the first place.
Dave.
Does this by Michael Waller of Brittania Motorcycles help at all?
He straightens a Victor swinging arm in this youtube video
https://www.youtube.com/watch?v=575ORdb3MFo&list=PL-f-b3vlEx-yY0j3qiwtmAj1Li8Zd52KA&index=2
Rob
I'd take it to Motoliner in Maidstone and get it done professionally.
Hi,
The video is quite interesting. He addressed the height differences but there seemed to be a slight twist as well. My one seems to be quite level but both end plates are slightly twisted clockwise ,looking from the rear, by perhaps only a few mm. This may not seem much at the spindle but add the distance to the sprocket teeth and then to the tyre and it increases proportionally. This is most evident on the wear marks on the tyre. I am not the stage of straightening it yet but will do some more accurate measuring and may find a local specialist to do it. I would hate to ruin it and have to get another which could also be out of shape.
The twist fits in with the enthusiastic use of the power of an A65 with a 750 big bore conversion pulling a sidecar loaded with family and camping gear on left hand corners.
I would think that, apart from the earliest ones, A65 swinging arms are more prone to this as they are not as robust as those on A10s. A10s being shorter and of a bigger diameter must be much stronger.
Dave