# 2 Cycle Engine from Bar Stock



## Brian Rupnow (Feb 6, 2016)

I am going to attempt to design and build a 2 cycle engine from bar stock, which uses no castings. I have spent a couple of days searching the internet for a 2 cycle engine which has a relatively low compression ratio, spark ignition, and can be machined using a conventional lathe and mill. I have found what I have been looking for, thanks to a member in the U.K., and although it is made from castings, it is a proven design so I know that the port layout positions are correct. The engine which I will be using as my reference is the "Wombat", originally designed  by Edgar T. Westbury in the 1930's or 40's. My design is going to be a radical departure from the original designers, so I am not concerned about copyright infringement, however, I want to give credit where credit is due. This engine will have a 1" bore, X 3/4" stroke single cylinder configuration with ball bearings on the crankshaft. It will be machined from aluminum with a cast iron liner, and have (gasp) cast iron rings.  It will have rotary valve induction. I am in no rush at all to get back into my machine shop, as I need some recovery time from 4 months of building my twin opposed i.c. engine. Stay tuned--This could be fun!!!---Brian


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## Brian Rupnow (Feb 6, 2016)

Yes, I know--looks pretty strange doesn't it!! This is "more or less" what the original casting would have looked like without the fins on it. It is correct in terms of bore, crankcase i.d. and size and positioning of ports. Now, I wouldn't try to machine this shape from solid in a million years.  However, I have to model this main body, and then all the parts that fit into it as accurately as I can, just to determine to my own satisfaction how everything fits together and how all the parts interact with each other. After doing that, I will be able to determine how I can modify the body shown here to make it more "machineable friendly".


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## Brian Rupnow (Feb 6, 2016)

There!!! That'll do me for today. All of the other parts which I am modelling, although they too have the same critical dimensions as the cast and machined parts, are being greatly simplified as I model them. This is to make them easy to machine from solid. I have to enter all the math data as I model the parts, so I will pull my detail drawings directly off the parts when I get ready to detail them. Some of the parts may get a bit of cosmetic  work if I think they look too "blocky" but I won't really have a good overview of that until everything is modeled.  I have found one error on the old original drawings. The dimension from the top of the cylinder down to the center of the exhaust port on the cylinder is 21/32:. The dimension on the liner is 11/16" but it is taken from the top of the liner, not the underside of the 1/16" thick liner "lip". This puts the exhaust ports in the liner offset from the cylinder port by 1/32". I have changed the hole position in the liner to match the port in the cylinder.


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## canadianhorsepower (Feb 7, 2016)

Brian
if you go hear you have a better view of the Hallman engine


http://modelenginenews.org/


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## lohring (Feb 7, 2016)

I built an engine like that in high school, but used a casting for the crankcase.  Bar stock engines have been built by serious model car and airplane racers for years.  Jim Allen's gallery shows his efforts with high performance 15 cc engines.  (Sign in required)  The late Wayne Trivin built his small engines from bar stock.  Here is a description on how he does it.

Lohring Miller


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## Brian Rupnow (Feb 7, 2016)

At this point I am beginning to get a much better understanding of how this two cycle engine works. The rotary valve is a new concept (for me). I still haven't redesigned the main body to make it more "machining friendly", but I have redesigned all of the ancillary parts to something that can be carved from bar stock on my lathe and mill. I haven't looked too closely at the ignition cam or points yet. I have an idea of how I am going to modify the cylinder head to match the upswept contour of the piston top--I just haven't done it yet.


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## Brian Rupnow (Feb 7, 2016)

So--My questions are answered. I can get my favorite Chrysler ignition points and adjusting block on there, and one of my store bought Traxxas Pro-15 carburetors. Now that I know that, I can start chopping and hacking at the main body.


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## Brian Rupnow (Feb 7, 2016)

This is what it looks like with the cylinder in "super simplified" form. All of the ports, bores, and bolt holes and mating surfaces are the same as the original model, and I have managed to squeeze in a few cooling fins. I can't make it any simpler than this and still make it from one piece and still have a chance to cool it somewhat. I did take the mounts away from the sides of the cylinder and add a separate baseplate to the bottom.


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## Brian Rupnow (Feb 7, 2016)

Luc--this is what the inside of the inlet housing looks like. Doing it this way allows me to have a good place to mount the ignition points.


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## Brian Rupnow (Feb 7, 2016)

You may be right. However, this is exactly how Edgar Westbury designed it. If it doesn't work, aluminum is cheap and my time is free.---Brian


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## Jasonb (Feb 8, 2016)

Brian, Westbury made the 1/4" circle recess about 3/16" deep and then blended the inlet hole into the bottom of the recess to give a much smoother airflow. Yours will be very turbulent.

Also look at your port heights as I mentioned elsewhere, you look to have them both the same height, normal practice is to have the exhaust higher than the transfer.


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## Brian Rupnow (Feb 8, 2016)

Okay---I'm hung up!! The original Westbury drawings I am working from seem to have a discrepancy on them related to the port positions. In a cut-away assembly drawing, he shows the exhaust ports quite clearly as being closer to the top of the cylinder than the upper inlet port. In his detail of the cylinder, he dimensions the exhaust port and top inlet port as being directly in line. Something is not right, and I have no other frame of reference to clarify which is correct. Since the port positioning is critical to the function of the engine, this project has come to a halt until I can either get clarification or abandon this project.---Brian


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## canadianhorsepower (Feb 8, 2016)

Brian Rupnow said:


> In a cut-away assembly drawing, he shows the exhaust ports quite clearly as being closer to the top of the cylinder than the upper inlet port.



This doesn't make sense, you have a rotary valve on the intake you cant see the intake port int's in the crankcase 



> In his detail of the cylinder, he dimensions the exhaust port and top inlet port as being directly in line.



assuming that this is not a high RPM engine you can go with 120 degrees (60/60) on the transfer port (s)
 and 160  degrees (80/80) on the exhaust port (s)


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## Jasonb (Feb 8, 2016)

canadianhorsepower said:


> This doesn't make sense, you have a rotary valve on the intake you cant see the intake port int's in the crankcase
> 
> 
> > I think brian means the top transfer port through the wall of the liner
> ...


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## canadianhorsepower (Feb 8, 2016)

Jasonb said:


> I have sent Brian a typical 2-stroke timing diagram which would agree with your figures and is why the exhaust needs to be higher so it is open for longer than the transfer



according to this drawing exhaust and transfer port are at 
the right place. I would scale this drawing and use the dimensions
I get. What do you think ??


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## Jasonb (Feb 8, 2016)

I have suggested to Brian that he uses his CAD drawing and turns the crank around noting the angles at which points the piston comes level with the top of exhaust and transfer and see which dimensions give the correct sort of timing. The liner drawing also has the two transfer ports closer together than the holes in the crankcase which adds to the problems.

Whichever dims are wrong the exhaust should be higher than the transfer.

EDIT, just looking at the drawing you have blown up and I notice the two transfer ports are not symetrical above & below the screw holes for the cover which suggests the 1/2" dimension given on the crankcase drawing is wrong and the 7/16" on the liner drawing more likely to be right


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## Jasonb (Feb 8, 2016)

This is where the errors are likely to be I would not mind betting that the 5/8" and the 11/16"  dims are the wrong way around


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## canadianhorsepower (Feb 8, 2016)

Jasonb said:


> This is where the errors are likely to be I would not mind betting that the 5/8" and the 11/16"  dims are the wrong way around



that is one of them
but assuming the rod is 1.74 long that would give 132.5 transfer OK
but only 133.95 exhaust :wall::wall:


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## Jasonb (Feb 8, 2016)

Rod is 1.563" stroke 0.75"


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## GailInNM (Feb 8, 2016)

Brian,
You may find ETW's design series on 2 stroke engines useful.
http://modelenginenews.org/etw/2s/index.html
http://modelenginenews.org/etw/2s/index.html#A4

First link is to the series and the second link to the start of the section on port design.
Gail in NM


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## canadianhorsepower (Feb 8, 2016)

Jasonb said:


> Rod is 1.563" stroke 0.75"



still only give 133.74 transfer and 154.7 exhaust 
I would be satisfied with this is a torque porting
but considering the size It should be good:hDe:


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## Brian Rupnow (Feb 8, 2016)

Okay, that's it!! There are enough anomalies in the original design, combined with the fact that as near as I can tell there are no records of anyone having built and ran this engine, that I am abandoning it. Not really a big deal, as it gave me a Sunday's worth of entertainment and did contribute somewhat to my knowledge of two cycle engines. Now it is time for me to ask for help. I was hoping to get by without laying out any money for plans, but that hasn't worked out. I have searched the internet for plans that I could buy, and that search came up dry as well. I even went to Chapters Bookstore in Barrie and to the Hobby Store in Barrie and they couldn't help me. So--This is what I want. Plans for a single cylinder, spark ignition, two cycle model engine that runs on gasoline or Coleman fuel, and has been actually built and ran by someone. I do not want plans for a glow engine nor a diesel engine. I do not want plans that have been made by someone but never "proven" by being built and ran. If you have a set of plans for what I want, and wish to help, please send them to [email protected] . If you know of a book that has these plans, please tell me the name of it, and possibly where I can purchase it. There is a lot of work in building a model engine, and as much as I enjoy it, I do not want to build a prototype of an engine which I don't as yet fully understand.---Thank You---Brian Rupnow


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## canadianhorsepower (Feb 8, 2016)

http://www.myhobbystore.co.uk/product/17485/busy-bee-pe23


http://www.myhobbystore.co.uk/product/17486/phoenix-pe24

those 2 are not bad
I just upload a book on 2 strokes engine



good luck


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## Brian Rupnow (Feb 8, 2016)

I have had my suspicions confirmed by a knowledgeable gentleman in the U.K.

_The Wombat was the last of Westbury's engines which he designed in the last few years of his life when he was not well. It is arguably a 1940's design built in the 1960's at a time when commercially built engines were more capable that this engine was ever likely to be, so there was never a lot of interest in it. 

We know that there have been a number of attempts to make this engine, we even know of the location of a set of patterns for it  :-\ But as you have found there are numerous mistakes in the drawings. It is believed that it could be made to go if you put together a timing diagram for it and redesigned accordingly.

If it was built and made to run it would be a very collectable/valuable engine. _


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## canadianhorsepower (Feb 8, 2016)

Brian Rupnow said:


> It is believed that it could be made to go if you put together a timing diagram for it and redesigned accordingly.
> If it was built and made to run it would be a very collectable/valuable engine. [/I]



I would be interested in giving it a try, 
were can I get a copy of the plans.

did you check the book on 2 stroke engine ??


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## kf2qd (Feb 8, 2016)

http://www.homemodelenginemachinist.com/downloads/60-model-airplane-engine-as-dwg-114.html

A link to the cad file for a .60 2-stroke bar stock engine. The one in may avatar picture.

And you might want to look at Schnuerle porting. Simpler, lighter piston and simpler head.


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## Brian Rupnow (Feb 8, 2016)

kf2qd---A few questions, if I may. Is that engine spark ignition, glow plug, or diesel? Did anyone actually build it? Are there any pictures or video of the engine running? What was the compression ratio?---Brian


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## Brian Rupnow (Feb 10, 2016)

I am curious about what the size limitations are on lapped pistons with no rings on them. I know it is commonly done on 1/2" cylinder/piston combinations. If I used a cast iron piston in a cast iron liner, life would be so much simpler in terms of the rings catching on the ports. I would like to do it with a 1" diameter cylinder. I don't have access to a Sunnen honing machine--just my lathe and mill. Bitter experience has shown me that I really suck at making cast iron rings. That is why, when I build an i.c. engine I always go with Viton rings. They are cheap, they seal perfectly, and they give instant compression. Trouble is, they wouldn't slide past a port without expanding into it and failing immediately. If it is possible to go with a lapped, ringless piston in a 1" diameter cylinder, what would be the downside of doing that?----Brian


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## petertha (Feb 10, 2016)

Brian, you might not want to dismiss bar stock glow engine designs just because glow was their original configuration. Looks like there are kits to convert methanol glow plug engines to spark ignition using CDI & replacement plugs that match the same glow plug thread. I have not delved into this myself but maybe these links will get you started or others have experience with conversions on commercial engines.

http://www.justengines.co.uk/acatalog/Customer_Feedback__and_Our_Experience.html
http://www.justengines.co.uk/acatalog/Ignition_Systems_for_Glow_Engines.html
http://www.ch-ignitions.com/index.php


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## GailInNM (Feb 10, 2016)

Brian, 
Lapped piston/cylinders were very common in the 1950- 1960 era glow plug model airplane engines with bores of 0.8 to 0.9 inches. A few were made with bores up to 1-1/8 inches that I know of. As I recall the chief limitation was the weight of the piston in cast-iron as these were relatively high speed engines and were difficult to balance with the large cast-iron piston. Most of these engines used a steel liner with the cast-iron piston because steel has a slightly greater coefficient of expansion than the cast-iron. As the piston crown generally runs hotter than the cylinder this gave a fairly uniform fit over the temperature range.
Gail in NM


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## Charles Lamont (Feb 11, 2016)

Brian Rupnow said:


> I don't have access to a Sunnen honing machine--just my lathe and mill. Bitter experience has shown me that I really suck at making cast iron rings.



You can buy iron piston rings, down to about 3/4".


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## Brian Rupnow (Feb 11, 2016)

Thank You, Petertha, Gail, and Charles.---Petertha brings up a very good point about using gasoline and a conventional spark ignition in the glow type engines. I had thought of that myself, and the only thing I thought might have to be done was to lower the compression a bit to prevent pre-ignition. I wasn't sure if the porting would still be compatible with running gasoline fuel and a spark ignition, but according to those links Petertha sent me it doesn't seem to be a problem.---Brian


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## canadianhorsepower (Feb 11, 2016)

> I had thought of that myself, and the only thing I thought might have to be done was to lower the compression a bit to prevent pre-ignition.



Brian, 
you don't even have to worry about the compression If you are talking methanol and gas the difference is so small, on the other hand if the engine was design to use nitro and you want to go gas then you will need to increase it



> I wasn't sure if the porting would still be compatible with running gasoline fuel and a spark ignition,



porting is only to maximize your volumetric efficiency at your desired RPM
When I was doing lumberjack event I had a Husky 272 ported at 166 int 132 trans and 200 ex 12/1 trap comp ratio. And had made an adapter to replace the plug and used Glow plug and ran fine


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## Brian Rupnow (Feb 11, 2016)

I have been studying on both Edgar Westbury's two cycle timing diagram for 2 strokes and on Malcolm stride's diagram on page 132 of "Miniature internal combustion engines".  When I add angular values to Westbury's diagram they come within one or two degrees of Malcolm stride's diagram which is given in degrees as opposed to Westbury's diagram which is given in fractions of piston travel. These dimensions are not to the center of the ports, but are to the point on the port closest to the direction of piston travel, so just at the point when the port begins to be uncovered by the piston. If anybody disagrees with what I have shown, please speak up. You will see that the piston travel I used is 3/4", which corresponds exactly with the piston travel in the Wombat engine. I should now be able to transpose these angular values to the Wombat, to see where the ports should be placed.---(I think)----Brian


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## canadianhorsepower (Feb 11, 2016)

> If anybody disagrees with what I have shown, please speak up. You will see that the piston travel I used is 3/4", which corresponds exactly with the piston travel in the Wombat engine. I should now be able to transpose these angular values to the Wombat, to see where the ports should be placed.---(I think)----Brian



Brian 
it's wrong you MUST use the rod dimension
with the same stroke and same exhaust opening in degree
if your rod is longer  by 200 thousand  your piston will need to be lower by80 thousand  check the book or free program I posted


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## Brian Rupnow (Feb 11, 2016)

Luc--Color me confused!! Did you post a formulae or just give me the number of degrees as in post #13. if you gave me a formulae, please give it again.---Brian


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## canadianhorsepower (Feb 11, 2016)

Brian Rupnow said:


> Luc--Color me confused!! Did you post a formulae or just give me the number of degrees as in post #13. if you gave me a formulae, please give it again.---Brian



I didn't post the formula I just gave the numbers
from this site
http://www.csgnetwork.com/directporttimingcalc.html
 and input
                         stroke   .750
                         rod       1.563
 before dead center  ( leave empty)
       duration degree        120        (that's for transfer)
   and hit the button
calculate height it will give you .1534
 that is the distance from bdc that your ports will close

if you change the 120 for you 160 then it will give you .2656
and thats the distance from bdc where your port exhaust will close

that gives you 110 thou both open not bad assuming there is a lot of port area

I hope I didn't confuse you more


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## GailInNM (Feb 11, 2016)

Brian,
The timing diagram that  ETW shows is the general timing diagram that is further used to calculate the rotational diagram that is shown for most engines. The rotational diagram has to take into account the rod length.

I attach a quick sketch to show what is meant.


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## Brian Rupnow (Feb 11, 2016)

Luc--where did you get the figure of 160?--also, if that calculation gives the distance from bottom dead center to the point where  the ports will close, then does it follow that from the top of the liner it would be stroke, minus the resultant figure of .1534 minus the height of the port opening?


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## Niels Abildgaard (Feb 11, 2016)

Charles Lamont said:


> You can buy iron piston rings, down to about 3/4".



Where please?


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## ixb1 (Feb 11, 2016)

Simple timing calc with graphical result
http://modelenginenews.org/design/tcalc/TCalcForm.php
http://modelenginenews.org/design/tcalc/TCalcFRVForm.php


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## canadianhorsepower (Feb 11, 2016)

> Luc--where did you get the figure of 160?--also, if that calculation gives the distance from bottom dead center to the point where  the ports will close,



That 160 is the measurement of that engine Wombat
and the distance is from BDC to top of port



> then does it follow that from the top of the liner it would be stroke, minus the resultant figure of .1534 minus the height of the port opening?



the .1534 is the total height opening of the port( transfer)
forget about that 3/16 port height they got in the drawing it's more confusing then anything else. 
I would make my sleeve .750 more then the top of my piston at BDC and go from there


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## canadianhorsepower (Feb 11, 2016)

Niels Abildgaard said:


> Where please?




http://www.adpistonring.com/RFQ.html


they start at .5


http://www.grovercorp.com/rings-and-seals/butt-cut-piston-rings.html


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## Brian Rupnow (Feb 11, 2016)

This is a layout based on what Gail showed. I end up with two resultant figures, 0.131" and 0.188" ---What are they?  Are they the height of the port? Are they the position of a port relative to something? Are the two angles I used (copied from Gail's layout) good numbers to use for a two stroke engine? Have I completely lost my mind???


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## canadianhorsepower (Feb 11, 2016)

> This is a layout based on what Gail showed. I end up with two resultant figures, 0.131" and 0.188" ---What are they?  Are they the height of the port? Are they the position of a port relative to something?



these are the distance from the top of your piston at Bottom Dead Center
to the top of the port respectively   .131 for transfer and .188 for exhaust.


_ now according to the drawing this engine would have 108.06 exhaust timing and 76 transfer port timing a leed of 22  _ *My SUGGESTION of timing is 80 for the exhaust and 60 for the transfer leed of 20 * 
with all the experience I have with 2 strokes engine the first one is to high specialty we are not using a tune pipe    just to clarify things were do you see transfer ports on the picture on the left or on the right


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## Brian Rupnow (Feb 11, 2016)

I see transfer ports on the left and exhaust ports on the right IN THE LEFT HAND VIEW. The projection on these views is backwards to what we are accustomed to in canada. However, this engine is sneaky--It has a slot in the side of the piston that uncovers the bottom transfer ports. Is this unusual?


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## Brian Rupnow (Feb 11, 2016)

I think I'll go upstairs now and soak my head!! I haven't felt this damned dumb since I took long division in school 60 years ago!!!


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## canadianhorsepower (Feb 11, 2016)

Brian Rupnow said:


> -It has a slot in the side of the piston that uncovers the bottom transfer ports. Is this unusual?



Not really on a rotary valve, common on piston ports.
one thing I can assure you if I build one of those that slot WONT be there:hDe:
there is a lot of trust on the piston skirt and it's open 45 degree.
I'll be making holes to match the port that would leave me more material on the intake side


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## Brian Rupnow (Feb 11, 2016)

My Goodness---What a huge can of worms I have opened. I've never really given a lot of thought to two stroke engines. My world of hot-rods and drag racing only ever involved four cycle engines. My engineering career really never had much to do with any kind of engine. Specialty "one of" machines and automation, but no engines. I never played with two cycle model airplanes (I did get one as a birthday gift when I was about 13, but never could get it to run.) My "hands on" experience with two cycle engines was limited to outboard motors, chainsaws, weed-eaters, and lawn mowers---and I never really repaired any of them, other than to change a sparkplug or blow out a plugged fuel line. I have learned more about two cycle engines in the last 5 days than I knew in my entire lifetime. The "simple little engine" that has no cams, no gears, no valves, no rocker arms, no pushrods, no lifters----has taken on a whole new mystery and mathematical complexity than I never had imagined. I still hope to build one--but the more I find out, the more I realize I have to find out even more, before committing time and energy to a project doomed to failure because I entered it blindly without fully understanding what I was doing. Thank you so much to all of you who are helping to educate me.---Brian


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## petertha (Feb 12, 2016)

Neils, re rings, I suspect the recommendation is 'pretty much any RC supplier'. Type 'piston ring' into the search box & behold. Now the deal here is, you must match the cylinder bore & finish & piston gap dimensions to the commercial engine from which it came. That's different than making a bore first & cutting rings to suit.

http://towerhobbies.com/?gclid=CICMrq2C88oCFZSEaQodH60O_w


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## grapegro (Feb 12, 2016)

Brian,  Could I suggest getting an old 2 stroke engine that is us and pulling it apart to gain some factual info.  Norm


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## Brian Rupnow (Feb 12, 2016)

Norm--I've thought of doing that. There is so much information out there, and so much conflicting information, that I am lost in space!! I know what I want--a slow and simple two stroke. I want to be able to make it on my lathe and mill. I would like to copy a tried and proven design so that I don't have to "experiment" with port spacing and positions. I know my most severe limitation---I suck at making cast iron rings. Much research has shown me that lapped pistons with no rings have a practical upper limit of about 1" diameter.  If I make it air cooled then I have to press or shrink fit the liner into an aluminum cylinder for proper heat transfer. If I make it water cooled, then I just have to bore the aluminum cylinder "size on size" with the outer diameter of the liner and let Loctite do my sealing--I won't have to worry about heat transfer.---Don't worry--I'm going somewhere with this. The 1912 Hubbard marine engine is a slow, simple two stroke with  a 24 mm diameter lapped piston, and no rings. I have a drawing here from the model engine fairy that shows what size the ports are, where they are located, and enough "general" information that I can replicate a clone of it using Solidworks. I called my local machine shop this afternoon and they do have a Sunnen Hone, and 1" is well within their range of work (in case I have to cheat). I have downloaded reams of information from the internet and printed it out to the point where my printer is screaming for a new ink cartridge. I have talked about it to my wife until she doesn't want to hear "Another thing about those stupid little engines I build!!" My head is in flames from thinking about two stroke engines.---I'm off to do some more research----Brian


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## kf2qd (Feb 12, 2016)

Brian Rupnow said:


> If I make it air cooled then I have to press or shrink fit the liner into an aluminum cylinder for proper heat transfer.



Unless you are trying to really push performance the sleeve just needs to have a close fit, but not a press fit. Oil will fill the space and provide the heat transfer. In a number of  older model airplane engines it was necessary to remove the sleeve to get enough clearance to remove the rod and piston. The most heat is created near the top of the cylinder and the head is responsible for most of the heat removed. Model airplane fuel is also the other method of heat removal. The originals used castor oil and did not burn it. The castor oil carried the heat away. Most 2 stroke model airplanes use a rather high oil content, but the oil does not burn, and carries the heat away.


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## lohring (Feb 13, 2016)

The timing isn't particularly critical if you aren't interested in performance.  There's a concept called port time area that's been measured across a wide variety of engines.  It is a measure of how much a given size port with a particular open time will flow.  Programs have been written that predict the power for a given  time area.  The Wombat's transfer and exhaust port dimensions are reversed as drawn.  They also are very conservative, even for an open exhaust engine.  There is too much exhaust port area for the transfer area and the rotary valve is overkill.  A cross flow engine is a lot harder to make than a piston port, Schnerle scavenged design.  I'll post some suggested modifications to the Wombat in a few days.

Someone has scanned Gordon Blair's book "Design and Simulation of Two Stroke Engines".  There is way more than you wanted to know about two strokes in it.  I have a simulation program based on the concepts in the book that's very helpful for two stroke design.  It has a significant learning curve.

Lohring Miller


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## Brian Rupnow (Feb 14, 2016)

I have abandoned this thread because of inconsistencies in the original drawings I worked from, and the realization that I don't really understand two stroke engines well enough to embark on building this sophisticated a model. I have instead turned my efforts to the design of an engine who's full size counterpart was built over a hundred years ago. If you wish to follow my efforts to make a working two stroke engine, then go to this link.---Brian
http://www.homemodelenginemachinist.com/showthread.php?t=25394


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## grapegro (Feb 14, 2016)

Hello Brian,
                Interesting move in your thoughts. What type of motor did you have in mind? I have a model that a friend and I have developed of an Atkinson cycle engine and am currently building an Otto Deutz engine of 1880 era, inverted single cyl, 50 mm bore. Eager to hear more along your path.
Norm


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## petertha (Feb 14, 2016)

lohring said:


> I have a simulation program based on the concepts in the book that's very helpful for two stroke design. It has a significant learning curve.
> Lohring Miller


 
Thanks for link. Very interesting. I was all pumped up about that program... until I saw the price. I'm sure it has some serious development behind it & a bargain for engine developers. Just cant justify it for my casual interest. Have you seen anything like this is for less $ or is it kind of get what you pay for thing?


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## Brian Rupnow (Feb 14, 2016)

grapegro said:


> Hello Brian,
> Interesting move in your thoughts. What type of motor did you have in mind? I have a model that a friend and I have developed of an Atkinson cycle engine and am currently building an Otto Deutz engine of 1880 era, inverted single cyl, 50 mm bore. Eager to hear more along your path.
> Norm


Norm--can you not see the link I posted?--Brian


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## lohring (Feb 15, 2016)

Mota is less expensive, but a lot less accurate.  I used it to help design pipes for a 35 cc engine, but the power predictions had no resemblance to the actual dyno curves.

Lohring Miller


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## lohring (Feb 20, 2016)

As promised, I quickly (for me) drew up a modified version of the Wombat.  I did not draw a carb or ignition system, just the internal parts.  You can use the Wombat systems or a Walboro WT-157-1 and a CD ignition.  I included a simple block crankcase as well as a more Wombat like version. Plates that I didn't draw cover the transfer passages in the block.  I think this is about as simple as a two stroke gets, but I assumed some engine building experience.  If anyone actually wants to build one, I would be glad to go into more detail.  The drawings haven't been checked so they probably contain errors.  I would draw an assembly as the minimum check.

The block, back plate, and head are aluminum; the crankshaft is steel with the crank pin case hardened; the liner is steel; the piston is cast iron; the wrist pin is hardened drill rod; and the connecting rod is high strength aluminum like 2024.  A leaded steel would work well for the liner and probably the crankshaft, but alloy steel like 4140 would be better.

This should be a 1/2 to 1 hp engine at 8,000 to 15,000 rpm.  It could easily become a 2 hp engine with higher timing and a tuned exhaust system.  It would need attention to fits and materials for higher power.

Lohring Miller


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## Brian Rupnow (Feb 20, 2016)

Lohring--Thank you for an incredible piece of work.---Brian


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## canadianhorsepower (Feb 21, 2016)

lohring said:


> As promised, I quickly (for me) drew up a modified version of the Wombat.  I did not draw a carb or ignition system, just the internal parts.  You can use the Wombat systems or a Walboro WT-157-1 and a CD ignition.  I included a simple block crankcase as well as a more Wombat like version. Plates that I didn't draw cover the transfer passages in the block.  I think this is about as simple as a two stroke gets, but I assumed some engine building experience.  If anyone actually wants to build one, I would be glad to go into more detail.  The drawings haven't been checked so they probably contain errors.  I would draw an assembly as the minimum check.
> Lohring Miller



Thanks for the drawing, quite a change from the original. I was checking the drawing closely because I would be interested in building one. Correct me if I`m wrong but the big end of the connecting rod give a radius of 1/4 and hole diameter of.312  the small end 7/16 radius and hole diameter .250

thanks


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## petertha (Feb 21, 2016)

eyeballing the pic, guessing 7/16 should be 'diameter'


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## canadianhorsepower (Feb 21, 2016)

petertha said:


> eyeballing the pic, guessing 7/16 should be 'diameter'



that's what I came up to

it gives the same wahl thickness .1875 at both end Thm:

but it could also mean that the edge have a radius of 1/4 

cheers


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## ozzie46 (Feb 21, 2016)

I believe the circles with the lines thru them are a drafting convention meaning "Diameter".
At least that's how I have read them.
 Ron


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## canadianhorsepower (Feb 21, 2016)

ozzie46 said:


> I believe the circles with the lines thru them are a drafting convention meaning "Diameter".
> At least that's how I have read them.
> Ron


I know that but read the plans and they don't match


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## Jasonb (Feb 22, 2016)

Should probably have been 7/32" R on the plan which would give the 7/16 diameter

Luc wall thickness will be 3/32" not 3/16"


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## canadianhorsepower (Feb 22, 2016)

Jasonb said:


> Luc wall thickness will be 3/32" not 3/16"


Jason 

.438-.250=.188/.0625=3 and that would be 3/16

or what did I do wrong


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## lohring (Feb 22, 2016)

You are right, it should be diameter.  As I said, the drawings haven't been checked.  I bet there are more mistakes.  Assemble the parts in a drawing to be sure everything fits.

Lohring Miller


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## Jasonb (Feb 22, 2016)

canadianhorsepower said:


> Jason
> 
> .438-.250=.188/.0625=3 and that would be 3/16
> 
> or what did I do wrong


 
You forgot there is only half the 3/16" on either side of the 1/4" hole which means 3/32" wall thickness

0.188/2 = 0.094


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## lohring (Mar 13, 2016)

A final note:
This is a lower cost series of programs for two stroke porting.  Some of the relationships are empirical but are based on decades if experience.  I'm not sure how they would apply to really small engines, but they should be a good guide.  Port time area calculators and port height versus angle programs apply to all two strokes.
http://www.porting-programs.com/

Lohring Miller


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