Been asked by a person building a special 1000cc guzzi with 40mm carbs if i can increase the valve size in the head is this possible
I think that there is not much meat between the valves it would not be possible
Any technical answers welcome
Possible but very expensive.All the round fins share the same castings so it is doable.Likely the same for the square fins.Ideally he’ll want to get higher compression pistons which means machining the combustion chambers meaning expensive .To fit the larger valves ( mid size LM type I guess) then you are likely to need to put larger seats in-you could possibly use the original smaller ones but that might mean too much heat transfer to the valves and them burning out.
Not aware of any larger valve size(s) you could go up to? Just FYI, according to my MG manual, tuning up the 850 Le Mans (1 & 2) for 40mm carbs involved only enlarging and polishing the inlet / exhaust ports to suit, 40mm exhausts, shims under the valve springs and B10 camshaft, valves stay as original size.
There have been big valve modifications in the past.Seem to remeber someone using Ducati valves and made to measure guides.Pretty sure Raceco, Chris Clarke and some American BOTT race teams did big valve heads on their race bikes, Will try to get the information together.All the bestSteve
Raceco did a “Killer Goose” version of the heads with LM1000 sized valves and porting to suit large carbs. I had a rather worn pair on a 992 engine I bought years ago, It did make for one rather fast ratty Spada.
Have got them there’ killagoose ’ heads on my mk 4…
Mr. Scarborough and myself took some Spada heads down to a very nice man in Rye, E Sussex, who gas flowed them and opened out Tim’s to take 36mm carbs and LM1 valves, he said he could do 40mm no problem. He used to work for some odd little companies called Ricardo and Cosworth, he was 85 years old, sadly no longer with us.G.