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vederstein

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I've done enough Steam and Stirling engines that I think I'm going to try my hand at a four stroke gas engine again. My first experience was a Webster where I failed to get the thing running.

My question revolves around valves.

Why always poppet valves? I had a hell of a time getting the Webster exhaust valve to seat and seal. Perhaps this was the root cause of my failure? (It could also have been the carburetor, which I made according to plans but learned later that that design was pretty much ****.)

In my steam engine designs I've had good success with spool valves. A piece of drill rod and a reamed hole will give an very close fit.

So, why can't an internal combustion engine have spool valves for the intake and exhaust?

As usual, I'll probably design my own engine with some inspiration from existing designs.

But the question still haunts me. Why can't an IC engine have spool valves?

Comments?

...Ved.
 

earlwb

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These engines don't use poppet valves:
You can look it up but HP made the VT-21, 25 and 49 series of Aspen valve four stroke engines. It tends to remind me of a Ducati motorcycle with the shaft drive to the overhead Aspen valve.
The Webra made T4-40, 60 and 80 (and maybe a 91) drum valve or rotary valve four stroke engines. They use a belt to the top of the engine, reminds me of a overhead camshaft engine.
OPS also made a 1.20 or 20cc drum valve four stroke engine too. it also looks like a overhead cam type of engine.
RCV made the inline and upright sleeve valve four stroke engines in .58,.60, .91, 1.30 sizes. They have moved on to making larger drone engines for the military and commercial interests though. These engines use a cylinder sleeve that rotates in the crankcase. There is a port at the top that rotates to the intake, then compression and exposes the glow plug, then on to the exhaust. The sleeve valve engine was used in some huge full size aircraft and bomber engines. The upright engines look quite normal but the inline engines are pretty neat though.

ref http://www.mecoa.com/hp/vt/21.htm

ref Webra T4-80

ref Steve Webb Models

ref RCV Engines Home | Specialists in multi-fuel engine technology

ref Sleeve valve - Wikipedia
 
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vederstein

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The valve design of the RCV engine I like quite a bit.

Based on this I think my ideas may have some merit. I'm going for simple, not exotic.

Therefore, when I get into the design work, I'll have to keep in mind of the valving. If one valve technology is a bust, then I need to design the engine in such a way that the valving can be changed.

Thanks,

...Ved.
 

earlwb

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You can peruse the model engines reviews here for various model engines such as the rotary valve and sleeve valve engines.

For example:
OPS 1.20, RCV engines, HP VT-21, and Webra T4 series engines. Some of the articles or reviews go into more detail with them taking the engines apart to study too.
OPS 20cc 4 stroke for example OPS 120 4C
RCV 58-CD RCV 58-CD
RCV 120-SP RCV 120-SP
WEBRA T4-40 Webra T4-40 (1)
HP VT-21 HP VT-21
 

ranger

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Hi,
Google “ Condor 120 model engine “. I had one in the early eighties, this engine was made by Dennis Allen of A. M. and Merco fame. It has a belt driven overhead rotary drum type valve incorporating both inlet and exhaust ports. The inlet entering from the side and the exhaust “ exhausting “ from the end, so relatively simple to machine the cylinder head. One advantage of building an OHV type of engine is, when you have the bottom end finished you can experiment with different types of valve design ie, OHC : Aspen etc by making another cylinder head and valve design to suit, still using the belt drive for operation.
Doug.
 

vederstein

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I wonder why these alternative valving mechanisms didn't hold up?

That Condor engine seems like a four stroke version of a Corliss steam engine valve. It seems very simple to me with the valving being one rotating assembly.

Perhaps carbon buildup and/or compression leaks were an issue?

I do like the concept though.


...Ved.
 

johwen

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Hello Ederstein,
There have been many different types of valving in the larger engines and success was never as good as the simple poppet valve. Sleeve valves were attempted dual sleeves then single sleeves rotary valves in head and all had the same problem and that was lubrication all burnt oil or if the didn't they seized. I have an engineer friend who has built Overhead roller valve heads for a ford 351 V/8 the rollers weigh a ton and the engine smokes and has to have a continuous drip oil feed. All this to extract more power so far a failure. The hours and cost if spent on developing the standard layout with cams an blowers and carburation would have been a tyre shredder.
The way to to get poppet valves to work and seal is not so hard if you are patient. first machine the stem in say 1/4 inch steps to size until you have the correct length, then machine the valve head and seat angle polish the stem. Put your retainer groove in the stem during first 1/4 inch. Do all this at the one setting so all is concentric.
When you do the valve seat if it is bronze insert put it in place first and then cut the seat. I usually don't cut the seat being bronze you only need to give the valve a tap with a brass punch and if the edge of the insert is sharp the valve will seat itself nicely. John
 

ranger

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I wonder why these alternative valving mechanisms didn't hold up?

That Condor engine seems like a four stroke version of a Corliss steam engine valve. It seems very simple to me with the valving being one rotating assembly.

Perhaps carbon buildup and/or compression leaks were an issue?

I do like the concept though.


...Ved.
I think the main problem with full size versions of this type of valve is to do with unequal temperatures and expansion of valve and head causing sealing issues. With model engines ie the Condor, running on Methanol and castor oil, ( total loss oil, mixed with fuel), this is less of an issue. You could probably use a cast iron sleeve in the head with a cast iron valve to minimise differential expansion problems.
Doug.
 

earlwb

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One problem was combustion chamber shape and then compression ratios. The rotary drum valve engines and top hat rotary valve engines are limited into how much compression they can get. The flat disc or Aspen Valve engines came out to help solve that problem. Then there is the combustion chamber shape cannot be optimized for best combustion.

The next problem was valve timing. Valve timing is somewhat limited due to a valve has to close before the next one opens. It is very difficult to get asymmetrical valve timing to increase performance. They did try multiple sleeves to solve the problem, but then that led to more problems than it was worth.

Then with sleeve valve engines there is a heat transfer problem from the moving cylinder sleeve outwards.
Then as Ranger stated, sealing and leakage is a problem too. With model engines it isn't as big of a problem as it is with full size engines.

But then they did solve most of the problems with the huge Centarus engines used by the British Aircraft, up until the jet age took off.
 

ranger

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One problem was combustion chamber shape and then compression ratios. The rotary drum valve engines and top hat rotary valve engines are limited into how much compression they can get. The flat disc or Aspen Valve engines came out to help solve that problem. Then there is the combustion chamber shape cannot be optimized for best combustion.

The next problem was valve timing. Valve timing is somewhat limited due to a valve has to close before the next one opens. It is very difficult to get asymmetrical valve timing to increase performance. They did try multiple sleeves to solve the problem, but then that led to more problems than it was worth.

Then with sleeve valve engines there is a heat transfer problem from the moving cylinder sleeve outwards.
Then as Ranger stated, sealing and leakage is a problem too. With model engines it isn't as big of a problem as it is with full size engines.

But then they did solve most of the problems with the huge Centarus engines used by the British Aircraft, up until the jet age took off.
I seem to remember reading somewhere that the first Bristol sleeve valve engines were rejected by the Air Ministry because they didn’t meet the MINIMUM requirements for oil consumption!!! Bristol had to increase machining tolerances to use more oil. Apparently the boffins decided if an engine didn’t use a certain amount of oil, it was likely to seize.
 

Anatol

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Hello Ved and all - this thread is very interesting to me as I continue to be interested in alternatives to the poppet valve. Historically it seems poppet valve became obligatory as pressure and rpm increased, ie with uninflow etc. Doug Self has lots on rotary valves for steam and IC, The Museum of RetroTechnology (I love his site) and its pretty much a story of ongoing failure. I'm also reminded of Tom Kimmel's remark, 'there are two kinds of valves, poppet and those that leak' or words to that effect. I'm not a locomotive guy but it seems there are lots of spool etc type there - they're essentially round versions of slide valves. I'm more interested in rotation types continuous opr reciprocating, like trevithicks on puffing devil. My interest derives from looking at automotive IC valves and specifically their return springs, which are huge, in order to close the valves fast - this is wasted engine energy. I don't have numbers but it seems to me a constant rotation valve would be most efficicient. Does anyone have ideas about this? prefereably with data to back them up :)
 

johwen

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Koenigseig in Sweden has perfected a fully electronic controlled poppet valve system that eliminates a camshaft throttle valve can shut down cylinders independently change and vary valve timing to suit engine revs etc. For slow speed the valves are just cracked open and to increase engine speed the valves are opened increasingly more and timing changed by opening the valves earlier and closing them later in a continuously varying manner. Power and torque have massive increases over conventional systems and a significant saving in fuel consumption. Valves are opened and closed by solenoids. Overall height of engines are much lower as there are no camshaft or valve operating gear as such Cheers Johwen John not sure i have spelt the manufacturers name correctly
 

earlwb

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Anatol, there is also the way Ducati and some others did it with poppet valves. They use the cams to both open and close the valves. They only use weak valve springs to help close the valves for starting and idling. it is Ducati's Desmodromic valve system. Thus they solved the problem with valves floating at high speed and the need for heavy extra strong springs.

Oh yeah, the Aspen valve system is what you might call a constant rotation valve.
 
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johwen

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Anatol, there is also the way Ducati and some others did it with poppet valves. They use the cams to both open and close the valves. They only use weak valve springs to help close the valves for starting and idling. it is Ducati's Desmodromic valve system. Thus they solved the problem with valves floating at high speed and the need for heavy extra strong springs.

Oh yeah, the Aspen valve system is what you might call a constant rotation valve.
Most High speed racing engines in MotoGP and Formula One grand prix engines use compressed air to control valves as springs don't work that well at the revolutions that they run at. They have compressors to pump up the pressure.. Cheers John
 

Anatol

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Anatol, there is also the way Ducati and some others did it with poppet valves. They use the cams to both open and close the valves. They only use weak valve springs to help close the valves for starting and idling. it is Ducati's Desmodromic valve system. Thus they solved the problem with valves floating at high speed and the need for heavy extra strong springs.

Oh yeah, the Aspen valve system is what you might call a constant rotation valve.
Earlwb - thanks I know about the desmodromic system.
Johwen, thanks also I've read about this technology. Mechatronics will be the answer, I'm watching piezoelectic valve research.
regarding the Aspen design - I googled it and got zip relevant hits. I went back through the thread but didn't find a link. Could someone please post a relevant link?
 

earlwb

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I had found some information. They seem to just lump in the Aspin valve engines with rotary valve engines.
and

They had a model engine review of the HP VT-21 engine here where they took it apart to view it: HP VT-21

I ran across this list of engines using a rotary valve.

I found a custaway view of the little HP VT-21 Rc model engine. I think that the Aspin valve is basically a vertical rotary valve whereas everyone else went with a horizontal rotary valve.
HP_VT21_cutaway_view.jpg
 
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vederstein

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I've been working on my four stroke for some time and the main goal of this engine is that it be easy to make. Think Webster but without the poppet valves.

Take a look at the video and let me know what you think. I haven't made it to the ignition yet, and I'm very open to suggestions.

...Ved.

 

minh-thanh

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I think it would be interesting to build and see how it works - if the valve is airtight I think the engine will run
The exhaust valve problem on the Webster engine
I know it's very difficult to make valves and valve seats airtight, but a lot of people have succeeded.
Just curious, can you describe the step by step how you lap a valve with valve seat ?
In a little bit of my experience, if I can't make the valve and the valve seat airtight, I would make a new valve (or a new valve seat or both) , and start over
 

vederstein

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It's been so long since I gave up on the Webster, that I don't quite remember the exact steps. I also tried a couple of different methods which all failed. I remember trying spinning the valve and seat in a drill. I remember trying to "coin" the seat with a press. I remember trying to spin the valve and seat with my fingers. Each try I made a new seat and valve. It certainly was an exercise in frustration.

I suspect that my Webster had leaking valves, but I also cannot discount the face that I made the carburetor from the Webster plans and didn't just buy a carburetor that is known to work.

Speaking of carburetors, does anyone have any recommendations? (Bore 7/8", stroke 7/8")

...Ved
 

earlwb

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Well I see some engines that they sell using silicon rubber or viton O-ring piston rings. I think you can simply use small silicon O-rings on your slide valves. They call their rubber rings Fluorine Rubber rings. They actually make single cylinder, twin cylinder and a V-4 cylinder one too. Anyway that might solve your sealing problem with the valves.
ref for example: 32cc Four-cylinder In-line Water-cooled Gasoline Engine for RC Car Ship
 

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