6mm valves

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Momus said:
Reducing the valve stem diameter and changing the material to stuff less than 60% the weight means improved port performance and potential cam shaft design. This is well understood and exploited.
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60% the weight with approximately 1/2 the modulus of steel and worse as it gets hot. Think of it as a flexible piece of spaghetti with a rubber diaphragm on the end for a valve head. Obviously an exaggeration but it makes the point. In order to get adequate stiffness (make up for the lower modulus) one would have to bulk up on the cross section which quickly eats into ones 60% weight advantage.

As for hundreds of racing miles durability; that would be good for about two vintage race weekends with full practice sessions each day and a Friday practice. As for well understood and exploited, I suspect you are citing NASCAR with water cooling, roller tip rockers, and megabucks development to assure valve motion control (numerical modeling, spin-tron seat bounce analysis ..etc). I had run skinnier Ti valves in the past with waisted stems within the ports and can say there are better ways to get extra reliable power out of a Norton twin.

It gets down to problem definition, ie. Is there a valve floating problem? If yes, in the case of a conventional stroke Commando, there are much better ways to address it instead of introducing new problems into ones build.

You can get skinnier stem valves in steel but there’s more than one good way to get air past the valve stem & guide area so skinnier stem gain is, at best, only incremental when compared to other options.
 
I'm sure things have changed by now, but a couple of decades ago, some of the top American race car guys were running 5/16" stem titanium valves in Chevy pushrod V8s, and they changed them out after every "hundreds of miles" race. They sold them off along with other "slightly used" race parts to lower buck racers. I bought a couple sets of them at the time for cutting down to big valve Norton valve head sizes, but didn't use them. Still sitting on the shelf gathering dust. Now that I'm building for landspeed racing instead of vintage road racing, I think I'll try them out on the next engine build.

I did successfully run 6 mm stem titanium valves in my Wood Rotax roadracer for several seasons with no problems, but that was a 4-valve DOHC head with significantly smaller valve heads, less unsupported stem length than a Norton, and no rocker arms to create side loading. With aluminum bronze valve guides and beryllium copper seats I had almost no wear on either. I thought it was a great combination, but I'm not as confidant about using 6 mm stems on the Norton, so I think I'll stick with the 5/16" stems. Also, the heads I use are already ported for flow with 5/16" stems, so I don't think smaller ones would offer any improvement in that area. Still, we're now seeing shorter stroke Nortons being built to run at much higher rpm than the usual 7,000 rpm Commando red line, so there might be a place where the lighter weight of titanium outweighs the negative characteristics. Only one way to find out, right?

Ken
 
Dances with Shrapnel said:
60% the weight with approximately 1/2 the modulus of steel and worse as it gets hot. Think of it as a flexible piece of spaghetti with a rubber diaphragm on the end for a valve head. Obviously an exaggeration but it makes the point. In order to get adequate stiffness (make up for the lower modulus) one would have to bulk up on the cross section which quickly eats into ones 60% weight advantage.

As for hundreds of racing miles durability; that would be good for about two vintage race weekends with full practice sessions each day and a Friday practice. As for well understood and exploited, I suspect you are citing NASCAR with water cooling, roller tip rockers, and megabucks development to assure valve motion control (numerical modeling, spin-tron seat bounce analysis ..etc). I had run skinnier Ti valves in the past with waisted stems within the ports and can say there are better ways to get extra reliable power out of a Norton twin.

It gets down to problem definition, ie. Is there a valve floating problem? If yes, in the case of a conventional stroke Commando, there are much better ways to address it instead of introducing new problems into ones build.

You can get skinnier stem valves in steel but there’s more than one good way to get air past the valve stem & guide area so skinnier stem gain is, at best, only incremental when compared to other options.
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Dances, I'm not suggesting that you can fit 6 mm Ti valves into a Norton and expect to race away into the sunset. The point is that with careful application there are big gains to be had. The reduction in spring force from very light valve gear would allow camshaft development. The 6 mm stems are willowy for sure but they are proven to work in the most highly developed pushrod 2 valve engines. In the Nascars they are around 6" long and lifted almost 3/4 of an inch for a total overhang from the guide approaching 3" at full lift. Each 725 cc cylinder can be producing 110 hp and exhausting through a valve just under 1-5/8" (41.00 mm) in diameter, so well thermally loaded. They get a fair rev too: up until a recent restrictor rule came in they were regularly run to 10000 rpm before gearing rules, to nearly 11000 (in qualifying). These engines also have to last the weekend, practise, qualifying and a race that could be up to 500 miles so perhaps 800 miles.
To me the professional Nascar experience demonstrates any concerns with the valves have been put to bed, and in applications with much lower loadings they are reliable and beneficial. I suppose an analogy would be with pistons. The steady reduction in weight, increase in reliability and reduction in friction along with improved ring sealing is one of the reasons why up to date versions of any number of racing 4 strokes in weekender's hands make more power, with more reliability, than the best works bikes from back in the day.
 
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lcrken said:
I'm sure things have changed by now, but a couple of decades ago, some of the top American race car guys were running 5/16" stem titanium valves in Chevy pushrod V8s, and they changed them out after every "hundreds of miles" race. They sold them off along with other "slightly used" race parts to lower buck racers. I bought a couple sets of them at the time for cutting down to big valve Norton valve head sizes, but didn't use them. Still sitting on the shelf gathering dust. Now that I'm building for landspeed racing instead of vintage road racing, I think I'll try them out on the next engine build.

I did successfully run 6 mm stem titanium valves in my Wood Rotax roadracer for several seasons with no problems, but that was a 4-valve DOHC head with significantly smaller valve heads, less unsupported stem length than a Norton, and no rocker arms to create side loading. With aluminum bronze valve guides and beryllium copper seats I had almost no wear on either. I thought it was a great combination, but I'm not as confidant about using 6 mm stems on the Norton, so I think I'll stick with the 5/16" stems. Also, the heads I use are already ported for flow with 5/16" stems, so I don't think smaller ones would offer any improvement in that area. Still, we're now seeing shorter stroke Nortons being built to run at much higher rpm than the usual 7,000 rpm Commando red line, so there might be a place where the lighter weight of titanium outweighs the negative characteristics. Only one way to find out, right?

Ken
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Ken, Chev have been running standard titanium inlet valves in their Corvette for 12 years now with a 56 head diameter and 8 mm stem: about the same ratio as a 42/6mm in a Norton.

The valves I have bought from Ebay are brand new; there are stacks of new surplus valves from when Chev went to the RO7 engine a few years ago.

.https://www.ebay.ca/itm/NASCAR-NEW-...ash=item489f2b186d:g:-gQAAOSw0t9U14jW&vxp=mtr


lcrken said:
I'm sure things have changed by now, but a couple of decades ago, some of the top American race car guys were running 5/16" stem titanium valves in Chevy pushrod V8s, and they changed them out after every "hundreds of miles" race. They sold them off along with other "slightly used" race parts to lower buck racers. I bought a couple sets of them at the time for cutting down to big valve Norton valve head sizes, but didn't use them. Still sitting on the shelf gathering dust. Now that I'm building for landspeed racing instead of vintage road racing, I think I'll try them out on the next engine build.

I did successfully run 6 mm stem titanium valves in my Wood Rotax roadracer for several seasons with no problems, but that was a 4-valve DOHC head with significantly smaller valve heads, less unsupported stem length than a Norton, and no rocker arms to create side loading. With aluminum bronze valve guides and beryllium copper seats I had almost no wear on either. I thought it was a great combination, but I'm not as confidant about using 6 mm stems on the Norton, so I think I'll stick with the 5/16" stems. Also, the heads I use are already ported for flow with 5/16" stems, so I don't think smaller ones would offer any improvement in that area. Still, we're now seeing shorter stroke Nortons being built to run at much higher rpm than the usual 7,000 rpm Commando red line, so there might be a place where the lighter weight of titanium outweighs the negative characteristics. Only one way to find out, right?

Ken
Click to expand...
 
Momus said:
Ken, Chev have been running standard titanium inlet valves in their Corvette for 12 years now with a 56 head diameter and 8 mm stem: about the same ratio as a 42/6mm in a Norton.

The valves I have bought from Ebay are brand new; there are stacks of new surplus valves from when Chev went to the RO7 engine a few years ago.

.https://www.ebay.ca/itm/NASCAR-NEW-...ash=item489f2b186d:g:-gQAAOSw0t9U14jW&vxp=mtr
Click to expand...

Wow. That's impressive, brand new Del West Ti intakes for about $15.00 each, shipping included. That's less than dealer cost for KPM Commando intakes! Years ago I got a quote from Del West to do a batch of Ti Commando valves. I don't recall the exact price, but it was WAY more than $15 per valve. Too late to try them in my current build, but might have to give them a try on the next one.

Ken
 
I'm putting similar cut down 6 mm in a B50MX Beeza. The Chev Corvette valves fit and are about AUD$150.
 
Dances with Shrapnel said:
What stem surface anti gall treatment do the Ti valve stems have; spray metal coating or Titanium Nitride?
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Del West uses plasma vapor deposition to put a chromium nitride coating on most of their Ti valves, but also offer other coatings for custom orders. I expect other manufacturers use their own secret sauce coatings. I've seen some in the past that used moly coatings.

More info on their Ti valves here:

http://delwestengineering.com/parts-titanium-valves/

Ken
 
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