Not much of a chance for weight saving in collets on valves, all place is used up by all types of collets, no different. But last night I checked my Argentinian scrap parts and found the taper in spring caps very different to common collets: Mostly the angle is 8-10 degrees as set on lathe, so 16-20 degrees angle included. But the parts I got look like 25-30 degrees and no old valves still got the wire groove on them, mods in Argentina I guess. One spring cap is brass or bronce, some are alu. What is the standard material for spring caps really ?
In case alu was used in production they could have decided on a wider taper in spring cap for the collets in alu not to get drawn down with time. But even so, no real reason to have an extra wire clip there, a common split collet type with that extra wide taper would do just fine as well. So no idea still about why . . . .
As to weight saving in this place, the alu pushrods I made are just 29 gr compared to solid plain steel originals at 39 gr, 10 gr difference !! No way I´d keep these, also the material is not quite suitable in all alu Vincent engines. You´d like to have some more heat growth in pushrods as well with alu cylinders and heads to maintain same valve play ideally . All you can do with steel is nil play cold. Will be a lot more with hot engine, so it is only one of several reasons for valve clatter.
The 10 mm alu pipes with 2 mm wall require a different assembly as they don´t drop through the adjuster threads: You have the cylinder and loose pushrod shrouds on engine and drop the alu types onto the follower cups. Only then you put the head on top of this and feed pushrods into head recesses while lowerimng the head down. A bit careful action here with wide angle shrouds but no real difficulty to do.
Some time ago I posted photos of the engine case shroud recesses which don´t align with follower cups by at least 1 mm. So I had shroud seal adapters made excentric for clearance for 10 mm alu tubes. Did they never rectify this offset or was this only on early B engines ?
Again, another of many questions about why . . . .
Vic