I do have a possible issue. Together with a mate I have come across a '70 A 65 Lightning puzzle. We could not resist and bought it.
The cylinder head has already been refurbished with new Colsibro guides and new Nucleus valves.
What makes me feel slightly uncomfortable is a measurement I have taken on the guides. The valve stem ends do protrude through the guides only 22 mm, every other head I have in reach shows a measurement of 24 mm.
10 years ago I had my own Lightning head refurbed at the shop which did the current head as well and I ended up with too long guides. The collar had hit the guides with a hot engine. Of course this went along with nasty noises.
If I do assemble the top collar with the collets to a naked valve I measure around 11.5 mm from stem end to the collars bottom end. This leaves me with 10,5 mm available travel for the collar when the valve is opening.
The cam is a standard 68-0437 with .306" lift resp. 7.8 mm. If the rocker Ratio was 1:1.2 I I'd end up with 9.4 mm valve lift or about 1 mm clearance.
My gut feeling is that this will not suffice due to the dynamic behaviour of the valve train and thermal expansion.
Is my assumption regarding the rocker ratio reasonable? Unfortunately I could not find a figure with the search function on the forum.
I am inclined to get the guides shortened by 2 mm.
Can you help me out with any input regarding my issue?
Thanks in advance and best regards