1968 B25 fork spring length

[MadPete]

Hello

Has anyone of this parish got an opinion on the correct spring length and/or compression rate for a set of 1968 B25 rod-damper forks. Any preferred suppliers of said springs? And what fork oil do B25 riders recommend?

Mr Ratio's tome suggests a compression rate of 34lb/inch or 26 1/2lb/inch. I can not find a related spring length although he notes up to 1/4inch variation in length.

I have seen springs lengths of 10 3/4inch to 10 7/8inch and rated at 30lb/inch quoted by draganfly and 11 inch by feked. I have no idea which might be preferable. They're relatively cheap so might be worth changing as I won't be doing it again. :0P

My current (old) springs are just over 10 7/8inch long but are not quite matched in length - plus a bit of (cosmetic) rust.

Any advice or recommendations much appreciated.

[JulianS]

The BSA factory literature gives the nominal length of the 34lb/inch springs, part 89 5036, as 10 3/4 inch to 10 7/8 inch. These are the same springs as used on heavier bikes like the A10.

[MadPete]

Thanks for the official specifications.

It seems the rod damper forks fitted to my B25 were shared around various bikes for a short time - eg. the A65. It seems some springs were originally rated at 34lb/inch but later B25 examples were rated at 26 lb/inch for more "comfort".  Commonly available items at 30lb/inch seems a fair compromise for a heavier rider. I could use the springs I have got as a few mm of variation is not considered critical (so I am told).

I suppose badly pitted/corroded stanchions are the worst problem and I might have to replace those but thankfully they are available. The design of these "exterior spring" forks seems to be less than optimal as regards corrosion = but I doubt they expected them to be used nearly 60 years later!

The only bits that seem to be more difficult to source in Uk are the bits for the damper valve at the end of the damper rod almost everything else can be found. Lets see how this progresses. :0)