# Searching for 2-stroke plan recomendation



## Brian Rupnow (Feb 5, 2016)

After building 10 four stroke i.c. engines, I would kind of like to try my hand at a two stroke. I have seen the Jan Ridder plans, and I know that people have problems getting these engines to run. In fact, the people who did get them to run had to modify them to do so. I have also seen the Rudy Kahoupt "Pioneer" two stroke with valves. The tiny engines similar to the Val are not what I want either.  I have not been successful in my search for a conventional two stroke that can be built from bar stock with no castings. something with a 7/8" or 1" bore, preferably. Does anyone have a recommendation for a two stroke that can be built with conventional mill and lathe?----Brian   [email protected]


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## johnny1320 (Feb 5, 2016)

[ame]https://www.youtube.com/watch?v=SL1uwRtqPWE[/ame]


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## johnny1320 (Feb 5, 2016)

This is right up your alley Brian, interesting design opposed twin with common combustion chamber one piston timing intake and the other exhaust


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## burkLane (Feb 5, 2016)

With your design skills I would consider a kind of reverse engineer gas trimmer motor design with your own flare added. Find an old scrapped one and take apart and use basic design elements or dimensions and then scale and build to suite your tooling. Something to think about anyway.  
And always following along on your builds whatever they are.


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## Brian Rupnow (Feb 5, 2016)

Johny1320--that is an awesome engine. Thank you for posting it. I was thinking more along the lines of a 2 stroke Maytag engine. Burklane--I have considered what you are suggesting.---Brian


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## Brian Rupnow (Feb 5, 2016)

My working knowledge of two strokes?--Well, they have piston, rings, connecting rod and crankshaft similar to 4 cycle engines. They do not have a camshaft nor valves. The crankcase is closed and will hold pressure. They combine the strokes--When the piston is moving up on compression, it creates a vacuum in the sealed crankcase. The carburetor feeds into the crankcase thru a one way valve, most commonly a piece of very thin spring steel called a reed valve. The lubricating oil is mixed with the fuel, so as the fuel enters the crankcase it lubricates the crankshaft bearings and both ends of the connecting rod, and the cylinder wall. The engine is fired by a sparkplug at or slightly in advance of top dead center and the piston begins to move down in the cylinder on the power stroke. As the piston moves down in the cylinder, this raises the pressure in the crankcase, and the reed valve under the carburetor snaps shut so the pressure in the crankcase can not escape. At some point in it's downward travel, after most of the burning fuel charge has expended it's energy but the piston is still moving down, the piston uncovers a port in the side of the cylinder which is connected to the pressurized crankcase. The fact that the fuel charge in the crankcase is pressurized makes it flow from the crankcase, thru the port in the side of the cylinder, and into the cylinder itself. At this point, the piston bottoms out and begins it's upward travel on the compression stroke. The side of the piston first closes off the port in the side in the side of the cylinder so that the charge of fuel which is now in the cylinder can not escape back into the crankcase. The piston then continues towards top dead center compressing the fuel charge and once again creating a vacuum in the crankcase to draw in more air/fuel mixture. Then the cycle repeats itself. The two cycle engine fires every time the piston reaches top dead center. From what I remember, the top of the piston is not flat, but has a "shape" to it which has something to do with keeping the burning fuel charge from blowing back thru the port into the crankcase---(I could be wrong on that reason.) ----So much for the theory behind two cycle engines.---Like everything else in life, the devil is in the details. If the piston has rings on it, how does it pass a port in the side of the cylinder without breaking the rings? How far down the stroke of the cylinder is the port so that it optimizes the power from the expanding fuel charge and still allows some time for the pressurized charge to flow upward from the crankcase into the cylinder. Would a model engine require seals on the crankshaft where it exits the crankcase, similar to 2 cycle snowmobile engines. (I once had a Yamaha snowmobile that had bad crankscase seals--it would go like stink at high speed but stall every time you slowed to an idle.) I know that there are many variations to what I have described. I know that the Jan Ridders design pressurizes the fuel charge in a separate compartment. I also know that two cycle chainsaws and weedeaters have flat top pistons, and I'm not sure how they get away with that. So you see, I know a great deal about 2 cycle engines. that is the good news. However, there is a great deal more that I don't know about 2 cycle engines, and that is what keeps me from boldly jumping into the design and fabrication of an engine which is doomed to failure because of the things I don't know. If I do this at all, I would much rather follow in someone else's footsteps.---Brian


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## Brian Rupnow (Feb 5, 2016)

No, I don't want diesel, glow, nor compression ignition engine plans. The old single cylinder Maytag engine would be just about perfect . The right speed and simplicity and a minimum of moving parts.


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## Brian Rupnow (Feb 5, 2016)

In my burst of enthusiastic writing, I just plain forgot the exhaust stroke, which coincides with the compression stroke. I like to run Viton rings, and since they are  a type of heat resistant rubber o-ring, I don't think they would survive sliding past intake or exhaust ports.--I have just learned that the shaped piston is a very old design, and that the flat top piston design was invented by a German, Adolph Schnurle in 1926 and it was based on having both ports on the same side of the cylinder with an arrangement whereby the exhaust port was in the center closest to the top of the cylinder, while the intake ports were arranged on each side of the exhaust port but still on the same side of the cylinder, closer to the bottom of the cylinder. This method was called "Loop scavenging" and provided a more consistent flame path and a much simpler piston and cylinder head design. ---And if I can't slide a Viton ring past the ports, then that would call for a piston that was lapped into the cylinder, with no rings.   i don't know whether my skills are up to that or not.


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## Brian Rupnow (Feb 5, 2016)

I have been revisiting the Jan Ridders "Two Stroke Puppy" design, and though I have heard of problems with it, (This is not my experience talking---It is based on threads from other builders about their difficulties in getting this engine to run) his approach of having a separate "expansion chamber" which does the job that the crankcase normally does solves a lot of problems. It does however call for a piston which is lapped into the bore of the cylinder, thus eliminating the rings completely to solve the issue of getting rings past the ports. His engine is designed in metric, with a 14 mm (.552") bore and a 15 mm (.591") stroke. I would probably scale that up to a 1" bore with a 1.07" stroke. This is a scale factor of 1.814:1---- The volume of the expansion chamber is not a linear calculation, so I might have to make the expansion chamber with one "adjustable" end so I could tweak the volume to it's most suitable size. Air cooled cylinders are much simpler to build than water cooled ones, but I understand this engine runs very hot so would benefit from water cooling.-One of my Australian friends built the "Puppy", and the only way he could get it to run was by increasing the piston head height to give it a higher compression ratio.--I will have to research this a little.


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## Brian Rupnow (Feb 5, 2016)

One of the companies I worked for during my career made hot chamber die-casting machines. The "gooseneck" or injection cylinder was made from H13 steel and was totally immersed in molten zinc all day. The injector piston was 1/2" diameter, and I think it too was H13 steel. The "goosenecks" were honed to fit the pistons using a Sunnen honing machine. I don't know if I have the ability in my home shop to hone a 1" cast iron piston to a close enough fit in a 1" cast iron cylinder or not. I have read a couple of posts where people who built the "two stroke puppy" with very close fitting pistons found that after a couple of days on the shelf the pistons would "seize" into the cylinders and they would have to dismantle the engines and press the pistons out.


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## Cogsy (Feb 5, 2016)

Two strokes using traditional rings use a locating pin in the ring groove to hold the ring gap in a fixed position away from the ports. The rings will happily jump right over the ports without catching as long as the ends are not exposed to the port where they can spring in and catch. I know you don't like cast iron rings but they would solve your ring problems here.


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## ixb1 (Feb 6, 2016)

This engine seems to be perfect for your skill level.
http://modelenginenews.org/tinysuper/index.html


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## Brian Rupnow (Feb 6, 2016)

Apparently E.T. Westbury designed a 2 cycle spark ignition engine called the "Wombat" but I can not find anything about who has the plans or where I could buy them. Can anyone help?---Brian


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## Brian Rupnow (Feb 6, 2016)

ixb1 said:


> This engine seems to be perfect for your skill level.
> http://modelenginenews.org/tinysuper/index.html


Thank you. I have had a look at the plans in that link, but they do specify it as being a "high speed" engine.


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## ixb1 (Feb 6, 2016)

And what take Boll aero 18 engine and scale up it two times (14.4 cc) ?
This is not high speed engine design,but very simple.


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## lohring (Feb 6, 2016)

The early model two strokes were piston ported with a cast iron piston running in a steel or cast iron sleeve.  I owned several Fox 35s in the 1950s with cast iron pistons and they ran very well for a long time.  

Duke Fox on pistons and liners:

Now, to the piston and cylinder.  For years the most popular model airplane piston materials were iron in  its various forms, (gray cast, ductile, and Mehanite). The advantage of  an iron piston is its low expansion, its dimensional stability. and the  fact that it does not soften noticeably with the heat reached in model  engines. The primary disadvantage is its weight, which is about 3 times  as much per cubic inch as aluminum. This is somewhat offset by the fact  that iron does have a higher modulus of elasticity than aluminum, and it  is possible to make an iron piston that's thinner than an aluminum one  and still maintain its shape. Iron pistons are usually run in soft steel  liners. Most of the model engines in the past 50 years have been built  in this combination. The iron can be fit very closely in the steel  liner. The expansion co-efficient of both are about the same, and should  the parts rub too hard, the iron tends to burnish and not gall. To the  user, an iron piston/steel liner motor has a freeness and a snap-over  compression not readily achieved with any other combination. 

The somewhat incomplete plan below is about as simple as an engine gets. It might have been designed for ignition, but should run fine on glow fuel.  I would make a one piece piston with a deflector like the picture below. A top locating flange on the liner is also easier.  I would also redraw it to be sure of the dimensions and details.

Lohring Miller


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## Brian Rupnow (Feb 6, 2016)

Lohring--I do like the look of that Hallam--unfortunately, I can't read it. When I print it out it is just too fuzzy. Can't read it on the screen either.---Brian


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## Charles Lamont (Feb 6, 2016)

Westbury designed a series of 30cc engines, the Atom I to Atom V, and the slightly smaller phoenix.

Plans for both available here:

http://www.myhobbystore.co.uk/group/33/plans?ItemsPerPage=48&SortOrder=0&Ops=173&sg=0&min=&max=

You probably know about the massive resources still available at the late Ron Chernich's site:

http://modelenginenews.org/

including a full list of westbury designs:

http://modelenginenews.org/etw/etw_engines.html

most 2S designs seem to use castings, but I should think you could adapt them.


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## Charles Lamont (Feb 6, 2016)

I know you said you don't want castings, but the Stuart Lightweight is a lovely little engine, and casting sets do come up for sale occasionally.

https://www.flickr.com/photos/[email protected]/18449858014/in/photostream/


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## Brian Rupnow (Feb 6, 2016)

Thank you very kindly gentlemen. I have secured a set of the 'Wombat" drawings, and they are printing out as I type this.---I appreciate the info on making piston rings.---Brian


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## Hopper (Feb 6, 2016)

Usually, two stroke piston rings are located by a pin in the groove in the piston that locates in a step filed into the ends of the ring. This stops the ring from rotating and is positioned so that the ring ends are kept clear of all port openings. Some engines have a series of holes for the port opening instead of one long slot, so the rings do not bulge out into the port. 

There is a ton of literature out there on two stroke port design, which is how they got away from the old peaked pistons. There is quite an art to it to ensure the fresh charge does not go straight out the exhaust port. 

There is a good primer on it here
http://edj.net/2stroke/BellPerformanceTuning/Bell Chapter 3.pdf

ISTR Maytag made a flat twin two stroke engine too. That would be a nice one to make. Would have two separate crankcase cavities, one for each cylinder, with a seal on the crankshaft in between.


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## lohring (Feb 7, 2016)

Brian Rupnow said:


> Lohring--I do like the look of that Hallam--unfortunately, I can't read it. When I print it out it is just too fuzzy. Can't read it on the screen either.---Brian



Brian

I can read the original but it is still a poor drawing.  I can email it to you if you want.  As someone pointed out, the http://modelenginenews.org/ has a wealth of information as well as the Hallam plan.

Lohring Miller
[email protected]


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## Brian Rupnow (Feb 10, 2016)

When I was a kid, I had an old Evinrude 2 cycle boat engine. It ran slow, idled slow, and started easily. This is far more in line with what I want t build. I can't believe that there are no engine plans for model versions of that type of engine out there somewhere.---Brian.


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## lohring (Feb 10, 2016)

I still have the plans from the engine I pictured, but I wouldn't build it today.  As was posted above, I would build a Schnerle ported engine with a piston port intake.  The world is full of examples of these engines in weedeaters and chain saws.  They are very inexpensive.  Homelite has one of the least expensive versions that costs less than $100.  The overhung crankshaft design would be easy to make.  I've been modifying this type of engine for years.  I can give you porting details.  You may be interested in a series of articles on two stroke design as well as one on modifications for model boat racing.  I can send you copies if you want.

Lohring Miller


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## barnesrickw (Feb 10, 2016)

Have three of these laying around.  Hoping two will still run.


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## Barnbikes (Feb 10, 2016)

Don't remember where I saw it but there was a 5 cylinder Maytag rotary engine around a couple years ago. Had a stationary crankshaft and the cylinders and crankcase spun.


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