Due to the asymmetric BSA frame, there are indeed differences between the parts on the left hand side and the right hand side of the bike.

First of all, the horizontal mudguard stays and the lifting stay are "handed". The left hand side is 1/8 longer than the right hand side. There's usually a letter "L" stamped on the left hand side flat end. If you try to fit them the other way round, your mudguard will not align with the rest of the bike, see pics. (If you try to fit Indian replicas, they will usually have been made symmetrical, with identical lengths left and right, giving a similar but less exaggerated problem).

The vertical mudguard stays have identical lengths L&R.

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Sorry Ron,
Yes M20
Going to follow Marks advice and slacken it all off.
I did email some pics to Jan who suggested may rack may be twisted, so I will start with that and see how it goes…

email (option): LarkesrATgeemail.com

The pannier frame bottom tubes have identical overall lengths left and right. However, to compensate for the asymmetric frame, the 3 L-shaped supporting brackets are shorter on the LHS, and longer on the RHS. But the mounting bracket is longer on the LHS, and shorter on the RHS. Everybody capito? 😁

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Jan, thanks for that makes my understanding much more informed, I had definitely assumed subconsciously they should be symmetrical.
One more details if you could be so kind, when together, does the top of the pannier frames run parallel to the carrier or at an angle??
Br
Scott

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They should be parallel.

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I have some NOS stays in stock.

https://pesltd.uk/?product=66-6886
https://pesltd.uk/?product=66-6887
https://pesltd.uk/?product=66-6945

The vertical stays have large holes at the top to cope with alignment errors.

Mark

email (option): pes.sales@btconnect.com

Bit of an updates chaps!
After an afternoon of slacking nuts off, lots of standing back and squinting I have two issue to address before I can continue with fitting these frames as they should be.
1, one of the two brackets that bolt into the top of the mudguard is longer than the other by about 1.5 times the thickness of the metal.
2, the carrier is twisted and to be honest I think this is the majority of my problem.
So off it all comes again to apply a little persuasion (possibly involving the map gas)!
I will report back on the results when these two are resolved.

email (option): LarkesrATgeemail.com

Having removed the carrier I have decided that my best plan is to replace the repaired mounts as no two are the same length or position on the carrier. Can you please tell me the distance between the carrier and pannier frame on your WM20 machines.
Thanks in advance, so many variables!!

email (option): LarkesrATgeemail.com