New Steve Maney valves with necked stems

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jseng1

jseng1

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I just got some 3mm oversize intake valves from Steve Maney and they have a necked down section near the valve head that helps increase flow. This is a change from his earlier versions. The waisted diameter is the same as the reduced diameter at the collet area. You can see where I machined/raised the collet location for Beehive springs.

New Steve Maney valves with necked stems
 
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I don't know of any other off the shelf Norton valves with this feature.
 
Pete Lovell had fitted some 9/32 valve to my 920 , years ago (1997), still running well.....!
 
Been having it done for decades. It's a simple task of chucking the valves up in a lathe. First set of valves I had done for a Commando road race bike were Ti with a moly type coating on the stem wear surface.
 
I didn't know Mic Hemmings was doing this. I'm trying to get some made up now. With a hardened surface its best to get them finished by the manufacturer before hardening.
 
I would not do that with a steel valve. Where they are necked in that photo, is where they usually break when you dong one. If the valves are Ti, it is common practice in modern motors, to use thinner stems for the whole length of the valve.
 
Necking valves like that is extremely common, even on new automotive engines.

However, I’d prefer them slimmer all the way, they have reduced life like that cos of reduced bearing surface area. But they’re lighter.
 
The best of both worlds is to neck the stem near the head for higher flow but leave the rest of the stem at 5/16" for longer life. The smaller stems do wear out the guides faster. The necked stems are at .280" diameter and that is thicker than either 7mm or the whimpy 6mm stems.
 
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