Swingarm Straightening

lcrken · Jul 4, 2020

I needed to straighten a swingarm for use in rebuilding my '73 750 Interstate. I wanted to use a later swingarm with the reinforcing gussets, but the only one I had was a bit bent. The tubes for the bronze bushes didn't line up, and the fork legs were twisted. I was able to line up the bushing tubes using a mandrel and v-blocks in the press, but didn't want to make a sturdy jig to tweaking the legs. This is my quick and dirty method using a mandrel, some clamps, and heat. It worked out quite well, The swingarm is straight, and fits the cradle without excessive binding.

Ken

cjandme · Jul 4, 2020

"Necessity is the mother of invention", or "Where there is a will there is a way", take your pick, either way you continue to amaze with you ingenuity and abilities, thanks for posting this. Cj

xbacksideslider · Jul 4, 2020

Beautiful, Ken. I take it that the step block/all-rod clamps through the steel table?

johnm · Jul 4, 2020

Has anyone ever found a straight swinging arm?

What I'm getting at is do they all twist with use or in small incidents ?

I hope they weren't originally made that way.

lcrken · Jul 4, 2020

xbacksideslider said:
Beautiful, Ken. I take it that the step block/all-rod clamps through the steel table?

Correct. I just used one of the holes already in the steel table. It used to have plastic machine tools (injection molding, etc.) bolted to it, so has an irrecgular variety of holes in it. It was a freebie many years ago, and now I couldn't live without it.

Ken

lcrken · Jul 4, 2020

johnm said:
Has anyone ever found a straight swinging arm?

What I'm getting at is do they all twist with use or in small incidents ?

I hope they weren't originally made that way.

Before deciding to straighten this one, I checked all the other ones I had. There were 5 other pre-MK3 swingarms, and one of them was true, with swingarm axis parallel to wheel axis. The others were off by varying amounts.

johnm · Jul 4, 2020

lcrken said:
Before deciding to straighten this one, I checked all the other ones I had. There were 5 other pre-MK3 swingarms, and one of them was true, with swingarm axis parallel to wheel axis. The others were off by varying amounts.

Yes that seems to be very common. The bike engineer I go to says most are twisted.

lcrken · Jul 4, 2020

To be fair to Norton, most of these swingarms were off of race bikes or basket cases that I bought for parts years ago. I know some of them had been crashed. I actually considered just buying a new one from Andover, but they were out of stock.

Ken

gortnipper · Jul 4, 2020

johnm said:
Yes that seems to be very common. The bike engineer I go to says most are twisted.

I had Steve at F1 check mine when I had it apart, and was all good.

Bernhard · Jul 4, 2020

johnm said:
Has anyone ever found a straight swinging arm?
I hope they weren't originally made that way.

Depends if it was English, or Italian made?

lcrken · Jul 5, 2020

Bernhard said:
Depends if it was English, or Italian made?

All the other ones I checked were pre-850. I think that means they were English made, but I'm not sure exactly when Norton started using the Italian made frames.

Ken

xbacksideslider · Jul 6, 2020

Another thing to check.
I guess that’s a good thing
Bad attempt at a joke

Swingarm Straightening

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