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Location:
Ipswich
Registered:
October 2003
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Location:
Finland
Registered:
November 2002
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Re: Possible stupid question regarding valves.
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Thu, 07 October 2004 14:22
 
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Round shape offers best pressure into seal surface.
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Location:
VIC, Sth Frankston.
Registered:
July 2003
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Re: Possible stupid question regarding valves.
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Thu, 07 October 2004 14:23
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i've wondered the same thing, like having square valves rather than round ones to maximise surface area, but they obviously didnt for a reason.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Possible stupid question regarding valves.
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Thu, 07 October 2004 14:27
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main thig is.. how do you stop the valve from rotating? if it is anything other than round, if it rotates, it won't seal, but with tound, it can be whatever rotation and still seal.
and as Jayem says, best seal against pressure, ie, maximum area for minimum circumference.
Cya, Stewart
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Location:
Rosanna, Melb
Registered:
June 2002
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Re: Possible stupid question regarding valves.
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Thu, 07 October 2004 14:33
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I read somewhere long ago that oval valves had been developed (by Honda maybe) a long while back, but they were immediately banned from racing and so no-one ever developed them. Afraid I can't remeber any more than that, but Google may know.
Hen
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I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
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Re: Possible stupid question regarding valves.
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Thu, 07 October 2004 15:58
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Even more elementary than that.
Try making an oval/square/heptagonal/anything other than round valve.....cheaply.
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Location:
VIC, Sth Frankston.
Registered:
July 2003
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 02:18
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| oldcorollas wrote on Fri, 08 October 2004 00:27 |
main thig is.. how do you stop the valve from rotating? if it is anything other than round, if it rotates, it won't seal, but with tound, it can be whatever rotation and still seal.
and as Jayem says, best seal against pressure, ie, maximum area for minimum circumference.
Cya, Stewart
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Square valve stems?
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Location:
tas
Registered:
June 2002
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 02:28
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yeah that would stop them from rotating. 
ha! also while your at it, why not have square springs, and square came lobes, now that is engineering at it's finest! 
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 03:11
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one of the race bikes had OVAL PISTONS!!! and i think 8valves per cylinder!!! (with two conrods!!)
they kept on with it for a while, spent a lot of money then gave up due to sealign issues?
from Bills page
http://www.billzilla.org/othercars.htm
now that's an interesting way to get more air into cylinders...
they actually put it into production with the NR750 too!!!
mmm ovals.....
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Location:
Canberra
Registered:
May 2002
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 03:24
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I've read that the built the oval piston motor because they worked out that a V8 would be the ideal motor for the class, but, they were limited to 4 cylinders.
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Location:
Rosanna, Melb
Registered:
June 2002
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 03:59
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Manufacturing oval valves/pistons would be a lot harder than round ones, but would be able to be done.
I was at a job interview this morning, and one thing the place was doing was looking at lathing oval pistons. The cutting head just moves back and forth bloody fast and in time with the rotation of the piston. Apparently few places are doing it, but I don't think they can get the spindle speeds high enough to make it viable for mass production yet.
You never know what might happen down the track.
Hen
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Location:
London
Registered:
July 2004
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 05:10
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Honda made the NR 500 4 stroke 8 valve engine in the late 70s early 80s to compete with the 500cc 2 strokes that other manufacturers were winning on. 500cc bikes were limited to a max of 4 cylinders so Honda effectively made a v8 with pistons paired into an oval shape and topped with 8 valves.
Didn't work though, the bike hardly ever finished and people joked that NR stood for Nearly Ready.
The bike pictured above is the Honda NR 750, released about a decade later in limited numbers. It didn't make any more power than other 4 valve per cyl bikes of its time and it cost 38,000 pounds! Only 3 were sold in the UK.
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Location:
Land of Oz
Registered:
June 2004
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 12:13
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Hi,
Bristol/Hawker-Siddely, in WW2, made a sleeve valve engine. It was a sleeve that was on the outside of the cylinder and it rotated back and forth, with ports in the sleeve to match up with the intake and exhaust pipes.
It was very efficient, reliable and very quiet. However, it was used only on a few engine designs, but their biggest and last engine to use it generated 3,500bhp with a 45litre capacity and 18 cylinders. It generated over 4,000bhp with water-menthanol injection.
There was no attempt to reduce this engine to something that could fit into a normal car, and these engines faded into history.
seeyuzz
river
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 13:03
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These weren't the only sleeve valve engines either; there were smaller ones made, but I can't remember much about it myself - seems to have disappeared into the dark cracks of history anyway.
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Location:
London
Registered:
July 2004
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 15:37
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River-
I remember reading about sleeve valve engines, seemed fairly efficient and a good way to overcome valvetrain inertia. Rotary valves were also an interesting concept that seems to have faded into history.
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Location:
Vancouver
Registered:
June 2004
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 17:41
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the NR750 was made to compete in european superbike races during the era of the 500GP 2-strokes. I think I made that pretty unclear, so this is what I menat - the NS500 2-stroke raced the "500GP" class, and the NR750 was supposed to take over for the RC30/VFR750 in "superbike"; different classes...
The 750 engines run a maximized balance of internal geometry that has rpms up to the best compromise of what can be achieved between bore vs. stroke vs. rpm vs. flame front travel of the fuels. Then only way to get a significant power advantage was to run higher rpms, and the only way to do that without having a smaller diameter cylinder was to run more cylinders. Because they were limited to 4 cylinders, they decided to make a V-8ish motor that had the geometry reminiscent of a V-8, but had the cylinder pairs linked to skirt the "4 cylinders" rule. What ended up happening was a production run of 500 bikes (called the NR750), necessary to homologate the bikes under competition rules to allow them to run them in the race series. Once the competitors caught news of this, and the almost assured domination, they protested, and the sanctioning body agreed that it would kill the class, so they amended the rules to describe "4 ROUND cylinders", leaving Honda with 500 VERY expensive motorcycles that collectors all snapped up in a heartbeat. Incidentally, the NR750 has a redline of something higher than the other companies could ever match, so Honda put a rev limiter in the bikes so the collectors who did ride them wouldn't blo them up (apparently the 750 is alright even up to about 17000rpm)
Incidentally, Honda used to make a bike with a 250cc V-8 that I seem to remember reading that Mike Hailwood rode in the '71 or '72 season
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Location:
Finland
Registered:
November 2002
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Re: Possible stupid question regarding valves.
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Fri, 08 October 2004 22:10
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| Quote: |
Manufacturing oval valves/pistons would be a lot harder than round ones, but would be able to be done.
I was at a job interview this morning, and one thing the place was doing was looking at lathing oval pistons. The cutting head just moves back and forth bloody fast and in time with the rotation of the piston. Apparently few places are doing it, but I don't think they can get the spindle speeds high enough to make it viable for mass production yet.
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Ford E-Max engines have oval pistons. Though it's oval by only 1mm or so.
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