An appeal for help

[Mick Hanna]

I have 2 x 1 1/8" SUs. The one fitted has the aluminium (?) piston; the other, which will need rebuilding one day, has a brass piston. 

I seem to remember reading on the old forum that the aluminium piston uses a spring, and the brass one is weighted and doesn't require a spring. Discuss.

Thanks again everyone.