In the interests of keeping up to date.... I also did some work last night.
Finished stripping down the "new" head. It's tidy.

The valve stems aren't the same - the inlet especially looks to have been either cut short, or made that way to reduce interference on the flow of the charge?


About an hour or so later after a dubious application of Solvol and a toothbrush...



Bit nicer.

Polished up the back face of the valves too...


and then gave them a bit of a grind. I only used the "fine" grinding paste because they were sealing nicely before, and I just wanted to ensure the mating face was good after the polish. Obviously I'll test the seals again after reassembly.

Terrible photo of the excellent valve tool I inherited from my Dad.




That's a big hole....

I also took some measurements of the inlet manifolds on each head. I'd read something about the evolution of the engine recently (must dig it out again), and that last photo made me curious....
Yup - they're different.
Head 1 (current) is 28.5mm / 1 1/8" internal diameter
Head 2 (new) is 32mm / 1 1/4" internal diameter.
I "believe" I'm right in thinking that if I want to use Head 2 (it's in better nick, has better valve stems and would appear to be "less old"), then I'm going to have to look for a new carb. IIRC the inlet manifold needs to be a consistent diameter/cross-sectional area for as much as is possible - which would mean that the carb would need to be consistent with that too. The current carb is an
AMAL Monobloc (389/229) which measures 1 1/8" across the "exit" hole (ie where the fuel/air mixture exits the carb). (Oddly, the AMAL website suggests (although they've taken off the details now) that that model Monoblox is a 1 5/32" which is ... err... 1 2.5/8" (I think...)). So... I'm a little confused about that .....
It does mean I have a reason to potentially get a better carb though.... According to this site (
https://surreycycles.com/carburettors/amal-monobloc-376-389/) there is no 1 1/4" Monobloc so I don't believe I can get the same carb and therefore have use of my now extensive collection of jets...) Something different then.... probably something like a Mk1 Concentric or something. I do have to say it's very tempting to look at some throaty Dellorto or something equally esoteric though.... might suit the "crazy ... like a fox" nature of the bike.
