Right size of valve seats?

[Chris.R.]

Hi folks, does anyone have an idea of the correct size (width) of the valve seats? The manual says 1.5mm as a maximum, but a former BSA mechanic says it may be wider for better heat transfer to the head!? Apparently it would not compromise the sealing-effect as the pressure of the combustion will help with this anyway?

I got mine re-cut (after 100'000km) at a good engine workshop and I saw they made them pretty wide and more than 1.5mm, I also can't see 3 angles cut!?

Any clues? I looked through the forum but coudna find et...

[GSPD750]

Sounds like it may be time for new ones if your machine shop cut them back more than the service limit of 1.5 mm.