2 Cycle Engine from Bar Stock

[ixb1]

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

 

[canadianhorsepower]

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

 

[canadianhorsepower]

Where please?

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


they start at .5


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

 

[Brian Rupnow]

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???

 

[canadianhorsepower]

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

 

[Brian Rupnow]

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?

 

[Brian Rupnow]

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!!!

 

[canadianhorsepower]

-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

 

[Brian Rupnow]

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

 

[petertha]

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

 

[grapegro]

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

 

[Brian Rupnow]

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

 

[kf2qd]

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.

 

[lohring]

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

 

[Brian Rupnow]

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

 

[grapegro]

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

 

[petertha]

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?

 

[Brian Rupnow]

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

 

[lohring]

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

 

[lohring]

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