New Superdream problem - bit of a bodge?

[McCabe-Thiele (Ted)]

Ted, the silver lable on the new one suggests to me its from a US model

The label is information about the exhaust system.

[McCabe-Thiele (Ted)]

I wonder if it's from a CM400T or CM auto Ted?

The sd site say its from a CM400T auto as it has a chain protector built into  the end of the swing arm that was later modified.

[Bryanj]

Yes the label is about exhaust but i think it was only on US bikes mate

[McCabe-Thiele (Ted)]

That explains why it's in such good condition.

[AshimotoK0]

It's sounds like the 250RS swinging arm Ted... prone to bad corrosion. Luckily, on my RS the PO had worked at British Aerospace and had chromate primed and painted it with aircraft paint. Decent UK S.D. ones are rare then I would imagine. I had a '400F' one that was longer than the one on my bike and turned out it was from a CJ250 ... a friend who's bike/engineering skills I respect said ... 'Ooh can I have it for my 400' as he considered it would be an improvement on the standard one.

I would just use it as it's so nice, using a longer chain and you may even find the bushes are OK as it looks like it's from a low mileage bike.

[K2-K6]

Agree with Ash, it's well within small adjustment category for optimisation of a motorcycle chassis geometry too.

Far more subtle than length of shock etc as it won't alter static fork angle and geometry.

Modern method make use of moving the swing arm pivot to change wheelbase, alter squat and anti squat etc by the ability to move the pivot both vertically and longitudinally. 

[McCabe-Thiele (Ted)]

Thanks for all your imputs

I'm going to keep the replacement swing arm, it's in too good a condition not to, I will see if the supplier has a suitable chain guard. I could cut off the front bracket from the old arm, not sure rivetting a bracket in the right place is a good idea.

The old swing arm had rotted from the inside, presumably water gets inside somehow.

[McCabe-Thiele (Ted)]

I'm still a little undecided about returning my longer rear swing arm.
I've been looking at an issue that might arise with my existing chain being too short using the longer arm.

My 400NA bike has a 16T front sprocket, 36T rear spocket, standard chain is a 530-100L part.
The 250 version uses 15T/41T spockets  chain is  530-102L part.

At a glance the extra 2 links might sort out the longer chain needed.

[K2-K6]

Conventionally speaking, you can only alter the chain by 2 links (two pins, effectively) to be able to join it again.

This, conveniently, gives you the amount of extension you get by measuring one pin to another (or chain dimension chart) to see how much further you can position the wheel away from front sprocket.

[Bryanj]

530 chain is available in many different lengths, get one too long and shorten it, you grind the heads off the two pins on one side plate and it falls apart

[andy120t]

Longer swing arm + a turbo = drag-racer 🙂

[Rozabikes Tim]

Longer swinger + a turbo = drag-racer 🙂

Or

[McCabe-Thiele (Ted)]

I'm hoping mine will not be that extreme!

[K2-K6]

I thought you said "an extra two links " Ted and not two whole chains 

[McCabe-Thiele (Ted)]

Imagine the length of the chain guard.