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PostPosted: Sat Apr 16, 2011 1:51 pm 
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In practice...it would indeed work!

The split cycle engine combines the intake, compression ,explosion, exhaust in one rotation of the crankshaft. In that sense it should be called a 2 cycle engine, some did, some don't.

In essence the engine looks like a 4 stroke engine with intake and exhaust valves , however one out of two pistons is used simply to compress air and the other provides the power stroke and the exhaust.

Here is a short animation from the Scuderi engineering group.

http://www.youtube.com/watch?v=Kogz4wed ... re=related


The Scuderi group calls this engine a 4 cycle. In fact Scuderi who claim the invention makes little mention if any of the original inventor of a similar engine, Dugald Clerk (a Scott) who around 1880 patented a two cylinder engine doing exactly the same thing (with some minor differences). The Clerk engine was then refered to as a 2 cycle engine and was designed to compete with the Nicholaus Otto's newly invented 4 cycle type that we know.

http://www.rider-and-road.com/Timelines/Era1.htm#1878 Clerk Two Cycle Engine

The merit of the Clerk design is that the engine was actually producing one power stroke per rotation, I too prefer to call it a 2 stroke engine. Dugald Clerk engine's gas-air intake was achieved through a conventional venturi and the compression stroke compressed a mixture, not just air as can be done today with direct injection.

I do believe that such a 2 stroke cycle is a superior design. Like other 2 stroke engines the torque and bhp per crank rotation would be far superior than that of 4 cycle engines . Unlike other 2 cycle engines the Clerk cycle engine would not suffer from conventional 2 cycle engines downsides: oil burning, port to cyclinder rings damage, unpredictable crankcase lubrication (in downhilling for instance) and longevity.

For the seven this type of engine could produce a high output/low weight and high rpm rates and yet could be built using mostly existing production engine components such as engine blocs, pistons, connecting rods, direct injection, flywheels, starters etc . As an illustration a 4 cylinder block could be used rebuilt, the crankshaft would have to be altered (or a new one machined) to make pistons work synchronised in pairs ; one pair at 180 deg from the other one. The cylinder head or maybe just the camshafts would have to be redesigned and I have not thought of it yet.

These are preliminary thoughts obviously. The Scuderi patent barrage should expire within three years. I think that ordinary 2.0L 4 cyclinder engines converted the Clerk way to 2 cycles could become 1.0 L displacement engines and possibly produce around 250 hp/liter, just like the 1. 0 L V4 regular 2 stroke race thing that was discussed last year on this forum.

I will be glad to discuss this idea with you if you are interested.

Philippe


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PostPosted: Sat Apr 16, 2011 5:14 pm 
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When Puch (and others) made two-cycle engines using two pistons with one combustion chamber they were commonly called "twingles".

http://en.wikipedia.org/wiki/Split-single

Seems that the Scuderi engine has a lot of promises and claims that could be applied to a normal engine too. And it would have more internal friction than a true 2 cycle twingle due to the valve train etc.

If it used direct fuel injection then the storage tank might work if it was big enough. If fuel is added to the air before the tank then you would have fuel dropping out of the mixture in the storage tank similar to fuel sticking to the walls of a longish intake runner.

All that air compression takes power and transferring it to another cylinder isn't going to increase the efficiency of doing it (there's two more valves in the way for one thing). And that assumes there is room under the hood for the air tank, which would have to be many times the engine displacement to deliver any appreciable advantage after going down a hill etc.

Put a real supercharger on a normal engine for pretty much the same results as air tanks and tricky crankshafts.

"For the seven this type of engine could produce a high output/low weight and high rpm rates and ..... [snip "

How much higher rpm than the current [stock] speed of super bike engines (14,000+ rpm) would be desirable? :wink:

Personally I thought the French "air engine" that had -30° "exhaust" was a better idea. :roll:
They were also looking for investors.

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PostPosted: Sat Apr 16, 2011 10:50 pm 
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quote.

Put a real supercharger on a normal engine for pretty much the same results as air tanks and tricky crankshafts.

"For the seven this type of engine could produce a high output/low weight and high rpm rates and ..... [snip "

How much higher rpm than the current [stock] speed of super bike engines (14,000+ rpm) would be desirable? :wink:

Personally I thought the French "air engine" that had -30° "exhaust" was a better idea. :roll:
They were also looking for investors.[/quote]


If you were to run a 2 stroke engine and a 4 stroke engine of the same displacement at the same speed the 2 stroke would always put out more torque and more hp. How much is another question. I would expect that the split cycle engine which is basically a 2 cycle one would outperform a conventional 4 stroke one. That's why I think it is worth considering.

Philippe


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PostPosted: Sat Apr 16, 2011 11:00 pm 
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The pumping cylinder can simply have a larger displacement and give you the supercharging that way. I think that must be part of anyone's design that's actually tried this.

It may not be the most efficient way to do this though. "Detroit Diesels" are 2 cycle with popet valves but I think they use a blower. It's a little simpler with a diesel 2-stroke because you don't worry about blowing fuel out the exhaust. They make quite large ones though, I remember someone saying a fery boat I was on that was based on a Liberty ship was using one... They sound different.

I think the 2-stroke diesels come out about even with their 4-stroke cousins, considering the different complexities, but don't know much about them.

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PostPosted: Sun Apr 17, 2011 12:04 am 
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philippe2 wrote:
If you were to run a 2 stroke engine and a 4 stroke engine of the same displacement at the same speed the 2 stroke would always put out more torque and more hp. How much is another question. I would expect that the split cycle engine which is basically a 2 cycle one would outperform a conventional 4 stroke one. That's why I think it is worth considering.

Philippe
I'm not that sure it would put out that much more (if any) than the original 4 banger. Along with the power stroke every revolution, small two cycle engines usually run at higher speeds than a 4 cycle engine partly due to less friction and hopefully better breathing (especially ones with a rotary valve). But the real thing to consider is that superbike engines (4 cycle) are putting out amazing amounts of power stock and even more power with blowers. My stock 988 cc GSXR-1000 engine is rated at 165 Hp @ 12,400 rpm.

The 2 air pumping cylinders have ring/piston friction, valve train friction etc that don't have a power stroke. The two remaining cylinders are doing the work of 4. You have the extra rotating weight of the crank throws (the way they show it), the extra 2 rods, pistons etc compared to a two cylinder, two cycle engine.

Using a 180° crank you would have a power stroke every 180° if its a 4 cylinder-4 cycle or a 2 cylinder-2 cycle. Since the air pumping and power pistons reach TDC pretty much at the same time the supercharging affect wouldn't happen unless the air cylinder was made a good bit larger and heavier which aren't that good for high rpms.

And to top it off, piston "superchargers" aren't the most efficient things. You have the same restrictions of the valves, air reversal etc as the cylinders you are trying to increase the efficiency of.

The way the video presented it there are the extra valves in the air transfer pipe to take advantage of the air pumping/storage of extra air when the engine isn't producing power. All that stuff adds complexity to the engine. And compressing air from the exhaust system when going down hill doesn't sound like a good way to get a nice fresh charge of oxygen in the storage tank.

I have an idea that if it really was such an advantage to have an engine like this (cost, power etc) that the companies that were making them beginning in the early 1900s would still have them on the market. Unless the change over could produce 40 or 50% more power you might as well bolt a supercharger on to the normal engine. A Busa with a blower is a real beast!

I think they threw out a lot of ideas to attract potential investors.

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PostPosted: Sun Apr 17, 2011 8:38 am 
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It is difficult to compare engines designed around different technologies. What I am asking here I know is to compare apples and oranges and bananas. The 2 stroke engine by the very nature of its design has long been a more powerful powerplant than its 4 stroke competitor both in diesel and gas fuels. The 2 stroke however had weaknesses (emissions, consumption, lubrication, longevity, etc) that nealy killed it until a new generation of design (fuel electronic injection/metering and crankcase oil injection) started changing that. I think that at least one Australian firm has produced a 2 stroke engine (orbital)that runs as clean and lean as a 4 stroke and outperforms the latter . With the split cycle even Scuderi does not seem to have solid numbers yet about performance. Preliminary test have shown tremendous gas saving results alegedly caused by the past TDC firing timing (something new) and the storage air tank idea. On high performance Scuderi seems to proceed with caution (they've shown 135 hp/1000cc which is obviously very shy). I suspect that the firm's goal is to establish its technology as environmentally superior and fuel frugality in order to secure investment and government backing which they did recently in the US.

What others like us can do with the split cycle design is entirely different and as I suggested a race engine can be built on a budget with conventional machine shop, dyno, emission testing equipment.

Philippe


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PostPosted: Sun Apr 17, 2011 10:09 am 
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I guess I just don’t get it, as applied to a Locost that is. Reference the 2L 4 cyl engine, if you deactivate 2 cylinders, and use them as a pump, then you are left with only 2 cylinders doing the work. Even if you get 2x the power out of these 2 cylinders, you might get the same power as the original 4 stroke 2L engine. But you still have the same weight and size. Where is the advantage in the Locost?

In addition, I would think that you would have to have at least 2x the displacement in the pump cylinders. Otherwise you would just be able to charge the working cylinders to ½ the pressure it would normally see if it were a 4 stroke. It doesn’t make sense for a Locost IMO. No real benefit as far as weight size or power.

Now take this 2L engine, convert all 4 cyl for 2 stroke operation, add a supercharger to replace the 2 cyl previously planned for pumping, add GDI (gas direct injection) maybe you’ve got the startings of a desirable engine; a 4 cyl - 2 stroke gas engine. But….depending on how much pressure you can get for scavaging, you may end up with no more power than a turbo’d (@14psi) 2L 4-stroke engine to start with. Conversely, if you can get a real 2 cyl engine operating as a 2 stroke with a supercharger for scavaging, now you are in Locost weight territory.

Fun to think about, for a while.

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PostPosted: Sun Apr 17, 2011 11:44 am 
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Just chiming in with some observations. ..

Pressure controlled Poppet valves (1 on each cylinder to limit the charge pressure in the crossover pipe) between the cylinders rather than mechanical valve train, less friction loss.
90 degrees or so would be a better angle, how does 70 degrees sound?
Mount a charge cooler between the banks. ..
Diesel engines as a matter of course inject the fuel charge after top dead center.
Since gasoline burns faster than diesel you can use a much shorter stroke and still get complete combustion.
Gasoline direct injection is now a fact rather than a theoretical, the mechanicals are available over the counter so someone is surely playing with them by now and creating baseline numbers.
A twin plug head on the power bank and re-machine one hole to fit an injector?
Overbore the precharge bank. .. basically a 2 stage piston type air compressor.
You would have a layer of exhaust gases that don't evacuate when the exhaust gas pressure equaled the pressure coming of the precharge bank. .. that might be a problem, I think it would greatly reduce your effective displacement.
I don't think you would gain anything over existing rotary superchargers but thats me.

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PostPosted: Sun Apr 17, 2011 2:43 pm 
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[quote="rx7locost"]I guess I just don’t get it, as applied to a Locost that is. Reference the 2L 4 cyl engine, if you deactivate 2 cylinders, and use them as a pump, then you are left with only 2 cylinders doing the work. Even if you get 2x the power out of these 2 cylinders, you might get the same power as the original 4 stroke 2L engine. But you still have the same weight and size. Where is the advantage in the Locost? Quote

R-Yes I did not get it at first either.
To follow the logic (if there is any) you have to look at my imaginary 2.0 L 4 cyl banger as a 1.0L 2 cylinder engine, that is only two cylinders burning fuel and making power strokes.
The two other cylinders are as Scuderi puts it an air pump, or a charging device. The original inventor Dugald Clerk called these pistons "displacers". Some here on the forum have suggested that a Roots or Eaton types supercharger would work better. I don't have the answer. The firing cylinders need about 150 psi, not so many car size superchargers will give you that. So the bottomline as I understand it is: a 2000cc turned into a 1000cc, the weight caused by the two pumping cylinders, pistons, rods etc, as well as their slowing down effect (compressing) requires a cost/ benefit analysis which I don't have. Let us say that if one was going to ask a regular supercharger to produce enough air (gpm) to feed two 500 cc firing cylinders @ 150 psi at up to 10,000 rpm we would need a gigantic piece of hardware too! Scuderi seems to think that they have the answers, but as I say they are still a little short on numbers.

So the hypothetical advantage of the split cycle for a small car is to get more ponnies out of a smaller displacement, meaning better gas mileage, less emissions and possibly a more interesting power curve than the stock 4 cylinder. I agree with your points however. At the end the 2 cylinder powerplant may not outperform a well prepared stock 4 cylinder, but it is a worthy case to toss around. And maybe someone will actually do it to find out, who knows, maybe even me :D


cheers:

Philippe


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PostPosted: Sun Apr 17, 2011 8:41 pm 
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philippe2 wrote:
The firing cylinders need about 150 psi, not so many car size superchargers will give you that.

In order to run the Scuderi engine doesn't really need higher air pressure than any other engine. But it does require more volume of air before it's compressed because they have to also charge the transfer pipe AND the storage air tank if they are really serious about that. It is also good to have higher pressure to get the air to quickly transfer into the power cylinder in time to do some good.

To get to 150 psi would require at least a 10:1 compression ratio on the pumping cylinder to overcome the compression of the power cylinder which is completing its compression stage.

A typical supercharger puts out between 6 to 20 psi. The engine compresses the 6 - 20 psi up by the compression ratio since the blower delivers the air during the intake phase (2 or 4 cycle).

A very rough example; 10 psi from the supercharger times 8:1 compression ~80 psi. 10 psi would take quite a bit less power than compressing to 150 psi.


Let us say that if one was going to ask a regular supercharger to produce enough air (gpm) to feed two 500 cc firing cylinders @ 150 psi at up to 10,000 rpm we would need a gigantic piece of hardware too!

Motorcycle turbo-chargers are quite small. Another point for not using a piston compressor.

So the hypothetical advantage of the split cycle for a small car is to get more ponnies out of a smaller displacement, meaning better gas mileage, less emissions and possibly a more interesting power curve than the stock 4 cylinder.

Unfortunately I don't think those are normally inter-related final products of getting more power out of less displacement (souping an engine up). It's like you can have 3 things, pick any two. I didn't see anything in the Scurderi engine that would have particularly resulted in less emissions. If anything I think if it does run higher combustion pressures, that would more likely result in higher nitrogen by products.

The torque curve on the GSXR is actually pretty flat from 4.5k to 12 k rpm. That range is already greater than most engines comfortably run at (12 - 4.5 = 7.5 k rpm). I just checked on the web and turbo Busa engines with a turbo are even flatter from ~2.8k to 12k rpm. And to top it off, the weight of the GSXR engine AND transmission is ~165 lbs.


I agree with your points however. At the end the 2 cylinder powerplant may not outperform a well prepared stock 4 cylinder, but it is a worthy case to toss around. And maybe someone will actually do it to find out, who knows, maybe even me :D

cheers:
Philippe
It's also interesting to see if these wondrous new engines etc ever get into production.

Someone mentioned that the extra valves wouldn't be that complicated.
The transfer pipe output end valve has to be externally activated because it is also used to allow air from either cylinder to charge the air tank AND it has to remain closed during the power stroke. The input side of the pipe was shown with a self activated poppet valve of some type.

As far as semi weird engines go, I like the diesels used on some submarines that had each cylinder arranged with two pistons that almost met at the center of the cylinder with a crankshaft and connecting rods etc at each end of the cylinder. The cranks were geared together. The pistons reached their TDC and BDC at the same time. If I remember correctly they were two cycle diesels.

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PostPosted: Sun Apr 17, 2011 10:08 pm 
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[quote="
A very rough example; 10 psi from the supercharger times 8:1 compression ~80 psi. 10 psi would take quite a bit less power than compressing to 150 psi.[/b]quote

Olrowdy,
I think you missed my point. Maybe I was not clear. My 150 psi figure is what the firing cylinders (in the Clerk-Scuderi design)would need from a external compressor if the charging pistons were not used at all. In other words the cycle would start with an externally precompressed air volume , the intake would happen through a popet valve, then there would be direct injection from the type of high pressure fuel injection pump used in diesels, then the ignition, then the power stroke and finally the return to TDC and exhaust through a popet valve. My point was, I wish I could do the above but I don't think that car size superchargers would exceed 30 psi. You confirmed that. :D If you are interested in weird engine designs you should get hold of the type that starts as a 4 stroke and then change to 2 strokes after a certain speed. It looks like there is no limit to human imagination.

Take care.

Philippe


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PostPosted: Sun Apr 17, 2011 11:33 pm 
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philippe2 wrote:
[quote="
A very rough example; 10 psi from the supercharger times 8:1 compression ~80 psi. 10 psi would take quite a bit less power than compressing to 150 psi.[/b]quote

Olrowdy,
I think you missed my point. Maybe I was not clear. My 150 psi figure is what the firing cylinders (in the Clerk-Scuderi design)would need from a external compressor if the charging pistons were not used at all.

OK, I couldn't figure out where the 150 psi came from but I figured I'd work with it. But why 150 psi? Was that in the video? If so I missed it while watching TV at the same time. :oops:

I mentioned this, "In order to run the Scuderi engine doesn't really need higher air pressure than any other engine."

Most normal two cycle engines don't have blowers. They just utilize other means to get fresh air into the cylinder before compression. Crankcase compression etc.

I was basically commenting that Scuderi got off on a tangent of apparently converting a normal engine (as a new design) with the complication of air pump cylinders and the air tank. Detroit Diesel has been building two cycle engines with low pressure blowers, piston controlled intake ports and exhaust valves for decades.


In other words the cycle would start with an externally precompressed air volume , the intake would happen through a popet valve, then there would be direct injection from the type of high pressure fuel injection pump used in diesels, then the ignition, then the power stroke and finally the return to TDC and exhaust through a popet valve. My point was, I wish I could do the above but I don't think that car size superchargers would exceed 30 psi. You confirmed that. :D

Philippe
Yep that pretty much describes a Detroit Diesel engine if you change your description to "intake side ports" and use a low pressure blower.

The air from the low pressure blower goes into a plenum which could be considered a small "air tank" which has been pre compressed. An intake valve could be used, but I'm pretty sure a two cycle has better control over scavenging with side ports rather than a top intake valve.

To convert the Detroit Diesel to a Scuderi, we could add another valve when the engine is used to re-compress the exhaust gas to the plenum so it doesn't need the blower for a [very] short time to [maybe] run again. 8)
---
Take a look at this for an unusual 4 cycle engine that used NO valves (as we commonly call them)! Now -that- would be a project!!

http://en.wikipedia.org/wiki/Knight_Engine

I found a drawing on the web of a 2 cycle model airplane engine that works on the same principle.

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PostPosted: Mon Apr 18, 2011 7:36 am 
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philippe2 wrote:
The 2 stroke however had weaknesses (emissions, consumption, lubrication, longevity, etc) that nealy killed it until a new generation of design (fuel electronic injection/metering and crankcase oil injection) started changing that.

I think that at least one Australian firm has produced a 2 stroke engine (orbital) that runs as clean and lean as a 4 stroke and outperforms the latter .


With the split cycle even Scuderi does not seem to have solid numbers yet about performance.
Philippe


2 strokes have very few weaknesses except emissions and is the one thats hard to beat.

Orbital (who do not produce anything being consultants/developers to the automotive industry) have licensed their high pressure air injector out to a few companies and Johnston Outboard engines have been using it for a few years now.

I think you should look at Scuderi's history, how long they have taken to achieve nothing and how many people they have taken. Damn computer 3D and whats it's done for the scamming industry, every week it seems theres a new engine thats going to save the world and the websites always have an "Investor" link :x


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PostPosted: Mon Apr 18, 2011 11:26 am 
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Thanks for your points cheapracer.

I have looked at Scuderi's history or some of it and I did not form a positive impression. My view is that Scuderi the father was an inventor who tried to make the Clerk split cycle design work commercially and did not succeed. His descendants seems to have taken his work and tried to run with it. From the outset (and this may not be entirely fair on my behalf) I see more energy being expanded by the firm in filing patents all over the place to corner the market than actual IC engine R&D or testing. I do not like the way they present (or appear to) the split cycle as a Scuderi invention when a quick search can show to anyone curious that the design dates back to 1880. So that's all my ranting.

I agree with your points about the 2 stroke: it is a superior design. I sustain my criticism however: emissions have caused the phasing out of these engines. The last 2 stroke car sold on the North American market I think was the Saab , a 3 cylinder inherited from DKW. The engine was free wheeling when the car was descelerating in order not to starve the crankcase from lubricating oil which shows that lubrication was an issue. With fuel injection the emission figures may change, I hope. I am keeping posted because I like the feel of a 2 cycle powerplant.

Philippe


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PostPosted: Mon Apr 18, 2011 12:31 pm 
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philippe2 wrote:
[snip]
I agree with your points about the 2 stroke: it is a superior design. I sustain my criticism however: emissions have caused the phasing out of these engines. The last 2 stroke car sold on the North American market I think was the Saab , a 3 cylinder inherited from DKW. The engine was free wheeling when the car was descelerating in order not to starve the crankcase from lubricating oil which shows that lubrication was an issue. With fuel injection the emission figures may change, I hope. I am keeping posted because I like the feel of a 2 cycle powerplant.

Philippe
That brings up some interesting ideas for a 2 cycle engine design. :idea:

1. Arrange the crankcase lubrication system like normal 4 cycle engine.
2. Use port intake for good scavenging.
3. Use a low pressure blower to feed the intake ports.
4. Use a computer controlled DFI system for good control of emissions etc.

No use trying to use my idea for profit though. :cry:

"Chrysler and Subaru have both developed two-strokes that stray further from the traditional two-stroke concepts. Rather than use the crankcase as the scavenging pump, they both use a belt-driven blower or supercharger to scavenge the cylinders. The crankcase remains a wet sump design like most automobile engines."

Read about it here,
http://www.snowgoer.com/output.cfm?id=1836523

The Toyota design in the article would be somewhat easy to duplicate for a home experimenter.

I did something similar to a lawn mower engine about 40 years ago except I ran it on compressed air for my tests. The camshaft ran at crank speed with slightly modified lobe profiles (done with a flat file and my lathe!!).

I later converted the engine [again] to use the mower piston as a crosshead with a double acting pneumatic cylinder for the power producing part. The output shaft of the cylinder is bolted to the original mower piston. I used an external off center disk mounted on the crank shaft to operate a slide valve to control the air to the pneumatic cylinder. None of this was anything new, I just wanted to see if I could do it. The Frankenstein of an engine had quite a bit of torque.

It is pretty messy looking with nylon hoses to deliver the air etc. I still have it [somewhere] in my garage. See my signature line for details.

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