71 replies to this topic

[gbaker]

The other valve thread sparked this question: Why poppet valves?

Obviously, the IC engine community has probably knocked the valve issue around for a century or so, but I'm not aware of any good explanation for why other forms of valving won't work at least as well. Is it one of those issues that was shelved decades ago, but which has not been updated to consider modern technologies?

Reed valves? Rotary valves? Blah, blah valves?

[Greg Locock]

I rather liked those rotary valves we looked at a while back. I think sealing is the problem, specifically the exhaust valve. When you think about it is is amazing that an exhaust poppet valve seals for as long as it does, as well as it does.

[bobqzzi]

Because nobody has come up with anything that works better- and it certainly hasn't been for the lack of trying.

[cheapracer]

Originally posted by bobqzzi
Because nobody has come up with anything that works better- and it certainly hasn't been for the lack of trying.

Some years ago sleeve valves were regarded as the next best if not as good (large car speak) and some engines had this system in production.

It has been for a lack of trying, are you aware of the investment required to establish an engine factory? The investment can buy small countrys and cant be expected to just drop it all to try something new. The rotary broke Mazda.

In the 2 stroke bike world, the 60's disc valves later replaced by reed valves on the inlet side and recent history exhaust rotary valves to vary exhaust port hieght/timing have made the 2 stroke flexible but still not clean enough.

Some years ago sleeve valves were regarded as the next best if not as good (large car speak) and some engines had this system in production.

Rotary valves pop there heads up on occasion - http://www.lortim.de...aspin/index.htm

other reading - http://www.a-car.com...ves/rotary.html

[Engineguy]

Why the poppet valve?

There is no sliding velocity between the sealing faces.

The sealing faces are round, so the sealing load is evenly distributed, and there are no alignment issues, no corners to seal, etc.

There is no sliding velocity between the sealing faces.

Round surfaces (even conical round surfaces) are simple and cheap to precision grind. Coaxiality (valve stem guide to valve seat) is also cheap and easy precision.

There is no sliding velocity between the sealing faces.

The conical sealing faces are self-centering.

There is no sliding velocity between the sealing faces.

The substantial contact force needed to effect a gas tight seal at combustion chamber pressures are pulled perfectly coaxial to the centroid of the sealing faces... a structurally perfect and elegant arrangement... and the ability to package the spring coaxially about stem is, again, a structurally perfect and elegant arrangement.

There is no sliding velocity between the sealing faces.

Good luck finding a better alternative... you're gonna need it. Being that most ideas seem to accept the very real problem of sliding sealing contact faces for the idealic purpose of eliminating the perceived problem of reciprication, I'd point out that we're handling reciprication just fine, thank you.

Additionally, any valving scheme that does away with the sheer genius of the round piston in a round cylinder accumulates additional strikes against it. I commend all those new engine inventors for trying... but I won't be betting any of my cash on them.

[Moon Tricky]

I personally quite like the simplicity of piston-ported opposed piston engines (aka Junkers), but they come with their own problems. Two strokes have their own problems in general, but trying to get exhaust gases to "go round a corner" to get out of a piston port around the other end of a cylinder has worse gas flow than going straight out of out of a hole. Unless you shape the piston heads to direct the flow, and then you affect the combustion process (non-ideal combustion volume leading to incomplete combustion). You've also got double the crevice volume. The advantage of the poppet valve is that when closed, it is completely flush with the surface.

[gbaker]

Originally posted by Engineguy
Why the poppet valve?

There is no sliding velocity between the sealing faces...

There is no sliding velocity between the sealing faces...

There is no sliding velocity between the sealing faces...

There is no sliding velocity between the sealing faces...

There is no sliding velocity between the sealing faces...

For that, and the other reasons you mention, I agree that the poppet appears to be the way to go. I am surprised, however, that the sliding issue remains so forceful an objection given material advances of late. A ceramic rotary sounds appealing. It may not match the poppet in sealing efficiency for street applications, but the racing world may be another story.

Then again, P chem and thermo were never my strong subjects.

[McGuire]

To me, poppet valves are sort of like democracy... totally screwed-up system, but still works far better than anything else yet devised.

[Ray Bell]

Is it just me?

Or is there a lot of repeated words, phrases and paragraphs in this thread?

[phantom II]

There is one important fact that has been overlooked in this thread and that is that there is no sliding velocity between the sealing faces...

Originally posted by Ray Bell
Is it just me?

Or is there a lot of repeated words, phrases and paragraphs in this thread?

[cheapracer]

I have a question, does anyone know if there is sliding velocity between the sealing faces or not?

[McGuire]

Originally posted by Moon Tricky
I personally quite like the simplicity of piston-ported opposed piston engines (aka Junkers), but they come with their own problems.

Hmm, interesting. How is the sliding velocity of its sealing faces?

[malbear]

I think that there is some initial sliding velocity with poppet valves as most systems impart a spinn to the valve to smeer or wipe off carbon deposits and not allow a partial or segment buildup causing a partial leak and possible gass tracking localised heating and failure.

Moon Tricky, I too much favour the simplicity of a piston port
opposed piston

[dosco]

Originally posted by McGuire


Hmm, interesting. How is the sliding velocity of its sealing faces?

Clearly we need a BEAM AXLE to fix the problem.

[Greg Locock]

And a fan to drive it.

[Moon Tricky]

Why not just take a motor, gear it up and connect it to a dynamo, and then power the motor from the dynamo? Surely that would work...

[m9a3r5i7o2n]

In the over hundred years that the poppet valve has been used in reciprocating engines I can recall only 3 big advancements in its operation,
# 1, the hollow valve stem filled with a low melting point material, (Sodium) around 1923.
# 2, the overall development of better materials and,
# 3, the device that makes the valve rotate slightly to wipe the face. Therefore the fact that the poppet valve is still around must somewhat prove that it was the best overall choice then and still is now!

Can anyone think of any others?

Edit, 0723-2007, After reading several additions below I must add the Hydraulic control of valve clearance!

The poppet valve is simple, cheap and overall it is very effective both in every day use and in high output engines! Besides all of this the many mechanics understand them!!! Can anyone visualize the problem of reeducating millions of mechanics on a completely new engine and valve system?

M.L. Anderson

[McGuire]

Excuse me for a moment... I am reflecting upon the possibility of ever educating mechanics about anything.

[malbear]

whenever I have exhibited ( at Stuttgart engine technology international or phillip Island moto GP) It has been the plastic model that is the fastest educator, Just turn it over twice and " O yes that works"

It takes about 10 seconds for the average Joe to get it But when I show a flat screen animation to academics It takes about 10minutes to get it.

[dosco]

Originally posted by malbear
But when I show a flat screen animation to academics It takes about 10minutes to get it.

That's b/c the average "academic" couldn't build their way out of a wet paper bag.

[Moon Tricky]

Originally posted by m9a3r5i7o2n
In the over hundred years that the poppet valve has been used in reciprocating engines I can recall only 3 big advancements in its operation, [...] Therefore the fact that the poppet valve is still around must somewhat prove that it was the best overall choice then and still is now!

The sleeve valve had some success in the early days, when poppet valves often suffered from excessive clatter.

[dosco]

Originally posted by Moon Tricky
The sleeve valve had some success in the early days, when poppet valves often suffered from excessive clatter.

As I recall, Ricardo had to do a boatload of R&D to get the sleeve valves to work correctly.

However, when they were finally sorted out, they worked very well.

[m9a3r5i7o2n]

However, when they (sleeves) were finally sorted out, they worked very well.

This may very well be true but it took them years to find out they were grinding them with the wrong method on the grinding wheels!! A question of not putting enough faith in the men on the grinders and the production engineers. It would be interesting to find out just how many Pounds Sterling were spent on that one!

Valve clatter? I believe that the Hydraulic Valve lifter put and end to this one, this only after the method used on the, to me, useless V-12/V16s of Cadillac. I have never been able to find out just who developed the Hyd. Lifter. Lincoln V-12 and Cadillac V-8 used very very similar lifters in 1936.

M. L. Anderson

[Moon Tricky]

Yes indeed, they did fix the clatter on poppet valves, putting them back in first place quite quickly. The other disadvantages of sleeve valves kept them behind, namely the high inertia of the moving parts, and difficulty maintaining a good seal.

[McGuire]

Originally posted by m9a3r5i7o2n
Valve clatter? I believe that the Hydraulic Valve lifter put and end to this one, this only after the method used on the, to me, useless V-12/V16s of Cadillac. I have never been able to find out just who developed the Hyd. Lifter. Lincoln V-12 and Cadillac V-8 used very very similar lifters in 1936.

M. L. Anderson

Depends what you mean by first, and what you mean by developed. Cynics might say that hydraulic followers were not "developed" for their first several years in high-volume production. (The '30s -- much of the problem was lubrication and filtration technology were not up to snuff. Just because you can build parts to very fine tolerances does not mean they will work.) On the other hand, you can find companies messing with hydraulic valve mechanisms before WWI. (Bollee for example.) Using hydraulic pressure to take up the valve lash is a rather obvious idea once you think about it, if difficult to implement.

This is why I don't really like to play the "first" game in automotive technical developments. It's like peeling an onion.

I don't why it is necessary to proclaim the Cadillac V12/V16 useless. The entire Duesenberg is "useless," I suppose, but I am glad they built it.

[cheapracer]

Originally posted by m9a3r5i7o2n
In the over hundred years that the poppet valve has been used in reciprocating engines I can recall only 3 big advancements in its operation,
# 1, the hollow valve stem filled with a low melting point material, (Sodium) around 1923.
# 2, the overall development of better materials and,
# 3, the device that makes the valve rotate slightly to wipe the face. Therefore the fact that the poppet valve is still around must somewhat prove that it was the best overall choice then and still is now!

#4, How about the pressurised and filtered oil system.

#3 - there is no "device" as such, the tappet is simply offset to the center of the valve stem as is a follower to its camshaft lobe or a cam lobe to a bucket.

[m9a3r5i7o2n]

Quote from; cheapracer.

#4, How about the pressurized and filtered oil system.

#3 - there is no "device" as such, the tappet is simply offset to the center of the valve stem as is a follower to its camshaft lobe or a cam lobe to a bucket

Pressurized oil systems and filters were around sometime before the 1936 Hydraulic valve lifters, I believe that Lincoln and Cadillac got filters in the late twenties. Pressurized oil systems were used very early on in the production of automobile engines. Modern oils didn't hurt either.

The use of just offsetting the two diameters may work on small valves but I wonder about larger valves such as used in Diesel engines I believe that the old Thomson company made a special device to do just that. However that is a long time ago.

M.L. Anderson

[McGuire]

Lots of engines of all types use valve rotators. They are generally integral to the valve spring retainers, so if you don't know what you are looking at you may never spot them.

[m9a3r5i7o2n]

Now I know why those little things eluded my observation, they were hiding from my view.
Well anyway we killed this subject!!!
M.L. Anderson

[McGuire]

Actually, valve rotators are made in a number of varieties, some of which are fairly interesting in their method of operation. I'm sure if you google "valve rotator" or suchlike it will lead to several hours of entertainment.

[cheapracer]

Originally posted by m9a3r5i7o2n



Pressurized oil systems and filters were around sometime before the 1936 Hydraulic valve lifters, I believe that Lincoln and Cadillac got filters in the late twenties. Pressurized oil systems were used very early on in the production of automobile engines. Modern oils didn't hurt either.

The use of just offsetting the two diameters may work on small valves but I wonder about larger valves such as used in Diesel engines I believe that the old Thomson company made a special device to do just that. However that is a long time ago.

M.L. Anderson

I missed a point here, are you suggesting pressurized sytems doesnt rate as an important advancement?

I dont venture into big engines having led a life as motorcycle, car mechanic and sometimes race mechanic and i can honestly say I dont recall ever seeing a valve rotator device in my field other than the common offset system.

[McGuire]

Then you have never seen a standard small-block Chevy V8 apart, you poor soul. (Or Buick, Ford, Olds, etc. etc.) Found this photo on the web a second ago (wouldn't want you to think it's my engine, too dirty)... This is an SBC with aftermarket roller rocker arms and stock valve springs and retainers. Those are valve rotators on the exhausts.

[cheapracer]

Originally posted by McGuire
Then you have never seen a standard small-block Chevy V8 apart, you poor soul. (Or Buick, Ford, Olds, etc. etc.) Found this photo on the web a second ago (wouldn't want you to think it's my engine, too dirty)... This is an SBC with aftermarket roller rocker arms and stock valve springs and retainers. Those are valve rotators on the exhausts.

Thanks for the pic. Well cover me with moss and call me pete, I think your correct, I dont think I've ever been inside a "standard" Chev V8. Notice the offset on the inlet. I am presuming the rotator is simply a ball thrust which is an aid to rotation and the actual rotation still comes from the tappet offset though??

[McGuire]

Not following you there at all. How could lifter rotation be effectively translated to the valve? There is a rocker arm between them.

On the intake valve shown there, you would never purposely run that much offset, could never get away with it. That rocker arm is loose or otherwise misaligned. If you ran it it that way it would prematurely wear out the valve guide for sure, among other bad things. At high rpm it might even pop a keeper and then the valve will fall into the cylinder.

These engines (American pushrod V8s that is) use more than bore offset to rotate the lifter. The cam lobe is tapered and the lifter face is crowned with about a 32" to 40" radius. The loadings are extremely high and if the lifter ever stops rotating, the lobe is wiped off the camshaft in short order -- like in ten minutes at no-load idle. Flat cam lobes have plagued the pushrod V8 off and on since it was born. If the materials or heat treat or lubrication wander off just a little in production, the monster returns. Of course, rollerizing the lifters will fix it for good, though that has problems too just like anything else.

However, valve rotation is not nearly as critical. In performance applications, typically one of the first things done is to throw away the valve rotators (and oil shields) and install lightweight steel, aluminum or titanium retainers. There is no easier way to reduce valvetrain recip mass. Now, there is no way the valve or seals can last as long without the rotator and shield, but they will last long enough. But for fleet and truck use you need rotators. Or if you are building a street engine and you want it to go 200,000 miles with no maintenance, exhaust rotators are probably in order.

[m9a3r5i7o2n]

Quote from McGuire;

Actually, valve rotators are made in a number of varieties, some of which are fairly interesting in their method of operation. I'm sure if you google "valve rotator" or suchlike it will lead to several hours of entertainment.

Valve rotator:
A unit that is placed on the end of the valve stem so that when the valve is opened and closed, the valve will rotate a small amount with each opening and closing. This gives longer valve life. Also called roto cap.


I did this and the very first one had a very good pair even putting them into motion, very informative. The address is below;

http://www.helical-t...ent/view/19/88/

Another one at;

http://www.tpub.com/...ss/14264_94.htm

Not quite as good but interesting just the same.

After reading about twenty of them one quickly finds out if you have a diesel engine especially, they had better have some form of valve rotation, if you have a long life engine on any type the same applies. Old aircraft engines that are famous for burning valves should be a special target to find a way to place rotators on the valves and especially on the exhaust!!!. Clean engines and filters also needed as some of them look to be subject to non-operation due to dirt in general.

Another point is the small amount of rotation each single opening of the valve due to fact that the engine is turning so many rpms that in just a few minutes of operation it has completed a full rotation.

M.L. Anderson

[cheapracer]

Originally posted by McGuire
Not following you there at all. How could lifter rotation be effectively translated to the valve? There is a rocker arm between them.

.

Your not following me because where I come from a rocker is also called a tappet. Lifters are known as either lifters or cam followers.

You still havent answered the question, is the Chev 'rotator' actually a rotation device or just merely an anti friction device in which the tappet, err rocker actually performs the rotation?

I have now had a look at some other rotators for big un's on the web following your tip and in fact some do do the work of rotating in some interesting ways.

[phantom II]

A tappet fits between the cam and the valve. If there is anything else there, such as a rocker or a push rod, the engine is tappetless. SOHC, DOHC and side valve engines have tappets. John DeLorean invented adjustible tappets. GM invented hydraulic tappets. All other tappets clearances are adjusted with shims. Where did you say you were from?

Originally posted by cheapracer


Your not following me because where I come from a rocker is also called a tappet. Lifters are known as either lifters or cam followers.

You still havent answered the question, is the Chev 'rotator' actually a rotation device or just merely an anti friction device in which the tappet, err rocker actually performs the rotation?

I have now had a look at some other rotators for big un's on the web following your tip and in fact some do do the work of rotating in some interesting ways.

[McGuire]

Originally posted by cheapracer


Your not following me because where I come from a rocker is also called a tappet. Lifters are known as either lifters or cam followers.

Then they talk WRONG where you come from. A lifter may be called a tappet or vice versa, but a rocker arm is never a lifter or a tappet. However, all three may be called followers.

See, it's perfectly clear. Or as my grandma used to say: your cat might have her kittens at the stove, but that does not make them biscuits.

[McGuire]

Originally posted by cheapracer


You still havent answered the question, is the Chev 'rotator' actually a rotation device or just merely an anti friction device in which the tappet, err rocker actually performs the rotation?

No, it's a real valve rotator, or what is called a "positive" or "active" rotator in the biz.

Note the intake side has no rotator; however, that doesn't mean the valve doesn't rotate. Unless the valve is keyed to the guide or seat, it is going to rotate to some extent, right? From there there are things that can be done to promote "passive rotation." For example, in "passive rotation" the valve is free to spin on the retainer when the valve is off the seat and spring pressure is momentarily in relative equilibrium. So they might use a 7 degree or so angle on the keepers in a service-life application, where in a race application they might use a 10 degree keeper angle to maintain a positive lock.

Some big diesel engines use "wing" rotators. There is a little propeller on the valve stem and the air flow through the port rotates the valve. I kid you not.

[McGuire]

Come to think of it, I have also seen wing rotators on lawn mowers and skid engines (portable farm powerplants).

[m9a3r5i7o2n]

One of these winged devices is shown at the address below.

http://www.marinedie...haust_valve.htm


Edit #1 http://chevy.tocmp.c...s/50csn0502.htm
M.L. Anderson

[McGuire]

Originally posted by m9a3r5i7o2n

After reading about twenty of them one quickly finds out if you have a diesel engine especially, they had better have some form of valve rotation, if you have a long life engine on any type the same applies. Old aircraft engines that are famous for burning valves should be a special target to find a way to place rotators on the valves and especially on the exhaust!!!. Clean engines and filters also needed as some of them look to be subject to non-operation due to dirt in general.

Another point is the small amount of rotation each single opening of the valve due to fact that the engine is turning so many rpms that in just a few minutes of operation it has completed a full rotation.

M.L. Anderson

Some really enormous engines (like 15" x 20" and so on) have rotators on the pistons. These are two-stroke diesel trunk-rod engines, and there is a pawl on a toothed circular track that advances every time the engine passes TDC. The idea is to impose highly symmetrical wear so they can run very tight skirt-to-wall clearance for a cylinder of that size, among other things.

[RDV]

m9a3r5i7o2n - # 3, the device that makes the valve rotate slightly to wipe the face. Therefore the fact that the poppet valve is still around must somewhat prove that it was the best overall choice then and still is now!

McGuire-No, it's a real valve rotator, or what is called a "positive" or "active" rotator in the biz.

...mmm.. so there is, contradicting=

There is no sliding velocity between the sealing faces...

[m9a3r5i7o2n]

There is no sliding velocity between the sealing faces...

I don’t see exactly your point as to sliding velocity but the amount on a poppet valve
with a rotator is very small per every other revolution. To see this in perspective go
to the
address at-

http://www.helical-t...15a95d124141acc

This may easily clear up what you speak of!

M.L. Anderson

[cheapracer]

Originally posted by McGuire


Then they talk WRONG where you come from. A lifter may be called a tappet or vice versa, but a rocker arm is never a lifter or a tappet. However, all three may be called followers.

See, it's perfectly clear. Or as my grandma used to say: your cat might have her kittens at the stove, but that does not make them biscuits.

I wonder if you use the term adjust the rockers or adjust the tappets?

No problem and you just go on and continue to call petrol gas.

[Canuck]

On my bike engines I adjust the pushrods as that's where the adjustment mechanism is - in the body of the pushrod. On my BMW I adjust the rockers, as that's where their adjustment lies. I don't think I've ever adjusted the lifters or tappets.

[phantom II]

I think you missed some inside jokes found in posts 5 thru 13.

Originally posted by m9a3r5i7o2n
There is no sliding velocity between the sealing faces...

I don’t see exactly your point as to sliding velocity but the amount on a poppet valve
with a rotator is very small per every other revolution. To see this in perspective go
to the
address at-

http://www.helical-t...15a95d124141acc

This may easily clear up what you speak of!

M.L. Anderson

[cheapracer]

Originally posted by phantom II
A tappet fits between the cam and the valve. If there is anything else there, such as a rocker or a push rod, the engine is tappetless. SOHC, DOHC and side valve engines have tappets. John DeLorean invented adjustible tappets. GM invented hydraulic tappets. All other tappets clearances are adjusted with shims. Where did you say you were from?

I didnt, but we do use the term adjust the tappets here usually via the tappet screws.

On rockerless SOHC (eg; FIAT) and most modern DOHC where I come from we call them buckets.

Kawasaki in some of their bikes used a wedge adjuster and on most Briggs and Stratton you grind the end of the valve to adjust the clearance, they qualify as your tappet engine and since B&S are the biggest engine producer in the world (80000 per day) this makes your statement that all other tappet clearances are adjusted with shims, well, wrong.

There are also some older sidevalve 'tappet' engines that the lifter/follower/tappet/shang ji (thought I would throw in the Chinese version too) is adjustable for length to adjust the clearance before Delorean was born, whats your take on that?

[McGuire]

Originally posted by cheapracer


Kawasaki in some of their bikes used a wedge adjuster and on most Briggs and Stratton you grind the end of the valve to adjust the clearance, they qualify as your tappet engine and since B&S are the biggest engine producer in the world (80000 per day) this makes your statement that all other tappet clearances are adjusted with shims, well, wrong.

That might be an interesting project, cataloging all the various valve adjustment schemes used though the years. Pros and cons, etc.

MY favorite shim setup was the original Z1 900cc Kawasaki. They chose to place the shim in a recess on top of the bucket (instead of under the bucket, where it belongs) and if at high rpm something went a little awry, the cam lobe would pick up the shim like a tiddlywink and fire it out the side of the cylinder head casting.

[cheapracer]

Originally posted by McGuire


MY favorite shim setup was the original Z1 900cc Kawasaki. They chose to place the shim in a recess on top of the bucket (instead of under the bucket, where it belongs) and if at high rpm something went a little awry, the cam lobe would pick up the shim like a tiddlywink and fire it out the side of the cylinder head casting.

As a qualified motorcycle mechanic (and qualified car mechanic but not a qualified metallurgist, re "hollowed bolts", ha ha) the Kawasaki shim setup was a dream, so easy to change shims with the simple Kawasaki tool that pushed down on the edge of the bucket - my point is that i just read that Suzuki's latest 1300 car engine has the same setup, back to the future.