Looking for necked down nitrided/tuftrided exhaust valves

[greg brillus]

Hi Tim , Actually the mods to the valves/ retainers will not raise things as much as it may seem. Clearance from the forked end of the rocker, the base of the upper guide and the collar is a slight issue......All will be reveled. I will start a thread on this whole project, but time on the bike is more important. But some advice from the likes of yourself would be Invaluable. Cheers for now...Greg

 

[vibrac]

Thats ok Greg so long as you have been that far ahead in your plans .Its sad if you had not and came to fit it in the frame..

 

[johnmead]

While we're on the subject, can you use big block Chev valves to make larger valves to fit a Vincent...? I need standard exhausts, but larger inlets with a head diameter of 1.925 This is about 1/8th larger OD than standard. I think the BBC valves have a stem of 0.372 I also want to raise the step half way up the stem by 0.080 and extend the upper stem by 1/4 of an inch. This is due to the cams I am using with radiused followers, which have a lift of about 0.433 of an inch or about 11 mm. I am using Gold Star springs, retainers, and modified upper guides to suit. Any thoughts..? Cheers.....Greg.

Back in 1977 I bought two Vincents and a whole bunch of parts off of a guy that drag raced a Vincent. In the stash of parts was a pair of 2-inch intake valves. In the same bag was the remains of the stem of the valves he used to make them. They were from a Cummins diesel. I called him and asked why he used them and he said that they were made from better steel than automobile valves. Now, this was back in the 70s and today's valve materials, especially with racing valves, is better.

I am probably using the same cams as you (Terry Prince MK5). I am using beehive valve springs and titanium retainers and keepers from C/D. Mine or in Terry's big bore heads so I do not have a problem with the location of the opening collar. I am also using cromo tube pushrods from Smith's and the geometry is good.

John Mead

 

[Kansas Bad Man]

What I have done Greg is to modify a standard valve . I heated the head of valve and with a special jig I made on the lathe I tulithe valve 3/16 of a inch on the press, then I built up the outside diameter of valve with like rod by heliarc welding. Then went to stress relive and heat treat. then I ground the valve to the size I needed. It was easy to do and worked a treat with zero problems.

Cheers

Max

excuse the sp

 

[Kansas Bad Man]

What I have done Greg is to modify a standard valve . I heated the head of valve and with a special jig I made on the lathe I tulip the valve 3/16 of a inch on the press, then I built up the outside diameter of valve with like rod by heliarc welding. Then went to stress relive and heat treat. Then I ground the valve to the size I needed. It was easy to do and worked a treat , zero problems.

Cheers

Max

excuse the sp

 

[mercurycrest]

While we're on the subject, can you use big block Chev valves to make larger valves to fit a Vincent...? I need standard exhausts, but larger inlets with a head diameter of 1.925 This is about 1/8th larger OD than standard. I think the BBC valves have a stem of 0.372 I also want to raise the step half way up the stem by 0.080 and extend the upper stem by 1/4 of an inch. This is due to the cams I am using with radiused followers, which have a lift of about 0.433 of an inch or about 11 mm. I am using Gold Star springs, retainers, and modified upper guides to suit. Any thoughts..? Cheers.....Greg.

Hi Greg,
The outfit that did my Racer's heads in the 70's used Manley BB Chevy valves. 1"-15/16" on intakes and 1.700" on exhausts. BSA Keepers. Never had any valve issues.
Cheers, John

 

[nkt267]

Do the larger valve heads still pass the top of the liner?
I have seen a pair of barrels recently that had the inlet side of the top of the liner ground away, almost like the valves would have clipped the liner otherwise. I was asked to check the bore size as the owner wanted to fit low expansion pistons in place of the Specialoid ones he had.. I've never seen this, has anyone??..John

 

[timetraveller]

I did this on all my competition engines but the reason is not for clearance for the valve. My reasoning was as follows. At low valve lifts with the piston moving downwards the suction is downwards and it seemed to me that more clearance to get the mixture flowing at low valve lifts should be a good thing. I have no idea whether it really improved things as I had no facilities for brake testing before and after. The cut out was in the cylinder head and at the top of the liner. All I can say was that it was the fastest production sprint bike until Ray Elgar made some serious mods and he then trashed my times. My best quarter mile was 13.06 and also 135+ mph at the end of as standing start half mile with the bike ridden to the meeting. Fifty years ago now!!!

 

[mercurycrest]

Timetraveller is absolutely correct on the cutout being for gas flow. Also, be aware that 45-deg. valve seats flow much better than 30-deg. ones. Someone should check into making new Rocker arms that are shorter on the pushrod side ala the Vincent Speedway engines. That would give a good boost to performance.
Cheers, John

 

[Kansas Bad Man]

Do the larger valve heads still pass the top of the liner?
I have seen a pair of barrels recently that had the inlet side of the top of the liner ground away, almost like the valves would have clipped the liner otherwise. I was asked to check the bore size as the owner wanted to fit low expansion pistons in place of the Specialoid ones he had.. I've never seen this, has anyone??..John

A garden hose with a adjustable nozzle can best show what is taking place and why the relief of the liner edge is helpful for intake performance. When the garden hose nozzle is first turned on it has a fan/ cone appearance . When the intake first starts to open there are two pressures that come into play one positive and one negative, the positive is the 14.2 atmospheric pressure( sea level ) filling the void or a absence of pressure caused by the piston in its downward motion. The negative pressure is being formed by a properly tuned exhaust (negative meaning less then atmospheric) . The relief of the liner prevents a unwanted deflector of the fan/cone.

Max

excuse the sp