Can anybody advise the correct length for an Atlas exhaust valve? I believe they are the same as the Dominator as the parts list indicates.
At some point the geometry of the valve gear was changed and valve length altered. What is your engine number?.
As robert says, they changed ...
Below is from an answer to a similar question, this is from John Dunn:-
The Dominator/650ss/Atlas have different combinations of valve length size and head diameter.
These range from lengths of between 99.5mm/99.9mm/100.2mm and 102.9mm.
The Dommi/650ss/Atlas head diameters range from between 33.3mm/35.7mm and 38.1mm
As Robert has asked for an engine number, I hope he has a way of stating which is correct for your engine!
Inlet valves head diameters for the post 1959 88,99 and 650 engines were 1.406" in dia. The bigger 1.50" valves were used on the Atlas 750 and Commando cylinder heads. (plus the 750 hybrids). The valve lengths changed after the spigotless barrels and heads made an appearance. They are slightly longer and the push rods for these engines slightly shorter. All by around 0.010" from engine number 125671 on. Which is around the time the first Commando bikes were coming off the production lines. Plus, just before this happened the rockers were changed to accommodate a pressure oil feed system.
That's sounds like our Atlas. Which is good to know as I'm about to do the valves. And fit a compression plate which will change the geometry a bit.
Robert, my engine number is 109240.
The current exhaust valve (a replacement) is 99.3mm long.
I am trying to improve the angle of contact between the valve stem and the tappet by making sure the pushrod length and valve length are compatible. At the moment either the valve is too long, or the pushrod is too short, or both.
Pushrod needs to be at least 7.4", maybe 7.44" long (not available) to improve the situation using the above length valve.
It could be that your ex valves are recessed a bit into the head (mine are!) , Somewhere there is a list of pushrod lengths , I have a vague memory that the 99 had the longest rods? ,with the easy life a classic gets now perhaps one of them could be used, they come to bits.Also there are some mushroom head adjusters around, might be usefull??
This is a fairly old info sheet provided by A/N.
Nice link Phil thanks. Have also just picked up some 7.44" long exhaust pushrods from ANIL so all should be significantly improved when assembled.
Subject closed and thanks to all contributors.