Hi All,
Last week I was asked to give an A10 iron head the once over,
It had been fitted with PB guides, The guides had squeezed tight onto the valve stems and on the exhaust side were easily pushed out with finger pressure
PB will expand more than the iron which is why I believe they then were compressed inwards
Anyway the head guide bores are bang on size so its getting cast guides, new valve seats, valves and springs
BSA fitted cast guides to alloy heads, the head I got for my RGS had iron guides in it, three of them were really tight, one less so
John