# 2-stroke, 2-cylinder engine?



## Jerd (Feb 14, 2008)

Hello everyone!

 I'm new to this comunity, and allready have a question 
I'm currently working on a 2 cycle glow engine (one cylinder), and
I'm more or less done fabricating it.

When doing a 2 cycle engine, the whole concept is to use the down stroke
to compress the airmixture, and then open the intake so the compressed air mixture
can enter the cylinder. How is this archived on a two-cylinder two-cycle engine? Do the
pistons work parallel, or do you have separate crankhouses?

(Ignore my bad English, it's not my native language, and specially technical English is kinda hard for me)

Cheers /Jon


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## jgarrett (Feb 14, 2008)

Jon, Can't answer your questions but welcome to the group. LOT of knowledge here from people willing to share it.
Show and tell us something about your equipment.
Julian G.


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## AllThumbs (Feb 14, 2008)

Generally, seperate crank cases.

Welcome!

Eric


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## Jerd (Feb 14, 2008)

AllThumbs  said:
			
		

> Generally, separate crank cases.
> 
> Welcome!
> 
> Eric



As i suspected, having them run parallel would put much stress on the crankshaft.

I have access to CNC lathes and mills. I have been working with MasterCam for 4 years, and as an engineer for 6 years. It all begun when i applied my mechanical knowledge creating a small oscillating steam engine for my girlfriends youngest brother. It was a much appreciated pressent. However, since I'm quite involved in active driving (cars) and races with racecars, I thought a small model engine would be a nice start introducing combustion engines to the "small ones" 

Cheers /Jon

Edit: It seams to be hard to find good, free, plans for model engines. Is it possible (and appreciated?) to upload PDF-plans of my oscillating steam engine and the 1-cylinder 2-stroke engine to this site?


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## Steam4ian (Feb 14, 2008)

G'day John.

Look up this site "http://modelenginenews.org/" for some info on building small engines, generally of aero type 2 stroke. Google "Jan Ridders" and "engines", Jan has some great work on 2 strokes, stirlings and the like complete with animations and explanations

Two stroke engines are basically 4 stroke engines but with two parts of the cycle happening simultaneously in different places; e.g. as compression takes place in the cylinder, induction is happening in another chamber. If you are using the crank case for induction then you need to separate the crank cases, one per cylinder. BTW Jan Ridders has a two stroke with open crank case but a double acting piston/cylinder like a steam engine. The induction and pre compression takes place at the back of the piston and normal compression and expansion happens at the top of the piston.

Hope this helps

Regards,
Ian


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## Stan (Feb 14, 2008)

A two stroke engine simply designates an engine that has a power stroke with every revolution of the crank. Air can be sourced from a piston or rotary compressor mounted on the engine and the exhaust can be via ports or valves in the head.

Detroit Diesel made two stroke diesels for more than forty years and they used a rotary supercharger (roots blower) and exhaust valves. Many very large engines driving gas pipeline compressors are two stroke natural gas with  vertical power cylinder and horizontal air compressor cylinders and exhaust valves.

Lots of different styles for anyone wanting to do a model.


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## Sprocket (Feb 14, 2008)

There was a build article in Model Engine Builder, issue 9 Nov./Dec. 2006. It's called the Hex-2 and is a two cycle, two cylinder engine. www.modelenginebuilder.com . Back
issues should be available. He used a couple of Cox .049 cylinders. It would at least show you how someone else solved that problem.

Doug


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## PolskiFran (Feb 14, 2008)

Hi Jerd, Separate crankcases were the norm in the past. I have pictures of full size marine (boat) engines from the early 1900's with separate crankcases. These engines could be purchased with 1 to 6 cylinders. While they used a common crankshaft and frame, another cylinder and crankcase was added in line to the others. This would probably be the way to go if attempting a model.

Hope this helps,
Frank


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## wildun (Feb 26, 2013)

Often the problem of crankcase compression is solved with opposing (boxer) pistons firing simultaneously and sharing a common crankcase but with opposing crankpins. 
These can be low vibration engines and work well except for a slight rocking couple caused by the cranks being offset to each other (looking from the top). One exhaust can be used for both cylinders.

Having said that, there were many very successful two stroke parallel twin motorcycle engines which had acceptable levels of vibration too and they had crankcases seperated by two opposing simple rubber seals on the crankshaft. (They had the two cranks pressed together.)


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## dman (Feb 26, 2013)

there are 3 ways to tackle a multi cylinder 2stroke and all are applied successfully somewhere. 

1. boxer/opposed arrangement. the cylinders fire at the same time thus the crank has 2 opposing pins. same pulses per rev but the pistons work to counter balance each other so less counterweight is needed on the crank. I believe this is used in model aviation on occasion.

2. parallel/inline arrangement, divided crankcase. functions as a set of independent engines that share a crankshaft. the sections are sealed from each other. more pulse per rev so it runs smoother. this is used in motorcycles snowmobiles and watercraft. also ultralight aircraft.

3. super charging. a pump feeds the crankcase (or ports directly but then you need lower end oiling). its usually positive displacement type with a displacement a bit more than the combined cylinder volume. vane style is popular for models and roots is used on full size engines though screw or wenkel could work and with the right engineering a centrifugal may work on full scale but on model scale I doubt it (centrifugal chargers don't scale nice and are harder to engineer because they have a pressure per tip velocity relationship rather than a volume per revolution relationship.) super charing has been done on model radial engines though it could work on any engine with a. evenly spread firing pattern. and is probably most notably use on large multi cylinder detroit diesel engines (yes there are full size 2 stroke diesels) sometimes with the addition of a turbo charger for boost. the super charger is the air displacer and he turbo adds charge density.  it was an unconventional design. they have pressurized oiling and use cam actuated poppet valves like a 4-stroke but fires every rev.


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## Niels Abildgaard (Feb 26, 2013)

A V 2 90 degree with a single common crancase will have half the pumping volume of a corresponding single cylinder.
This is more than enough for starting and real power from two strokes come from the tuned exhaust pipes anyway.
Vibrations  and balance is better than  all othe two cylinder configurations and mass is only better for 180 degre two crank engines.
I have a CAD picture somewhere but in meantime enjoy a picture of worlds most best single cylinder motorbike.

Kind regards

Niels


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## lohring (Feb 26, 2013)

The mechanically simple, crankcase pump type two stroke is one of the most complex engines ever developed.  Modern versions are all about fluid flow and taking advantage of the pressure waves driven by the pulsating nature of the engine.  The crankcase compression is only needed for starting since, as was noted, the tuned pipe provides the varying pressures to draw in mixture and then supercharge the cylinder.  

For a better understanding start with the Wikipedia article and it's references, then go to the Pit Lane discussion (requires log in) on the Aprilia 125 by several of the world's most knowledgeable two stroke designers.  That discussion is approaching 100 pages and is a course in itself.  For a modern, high speed uniflow design take a look at the Eco motors engine.  The picture below is a very simple flow visualization that illustrates how engine builders have tried to figure out what happens in a running engine.

Lohring Miller


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## dman (Feb 26, 2013)

2 strokes are interesting because they are so sensitive to flow dynamics.
a 90deg v should run. but i can't say i remember seeing any examples of it in production and on a one off engine it might need extra tuning to get right. most engineers don't try it because there is a level of unevenness to it. evenness doesn't matter as much as many think it would but it's a place designers like to start. i guess the most vibrations come from the crank imbalance with the tall heavy pistons that 2 strokes need to close off the ports. it would be great for a motorcycle but i have to wonder if the same idle quality and off idle torque is achieved. i understand the principles that go into it but i always figure the exhaust tuning would need a fair amount of rpm to take over from the bottom end pumping.


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## canadianhorsepower (Feb 26, 2013)

> [/i understand the principles that go into it but i always figure the exhaust tuning would need a fair amount of rpm to take over from the bottom end pumpingQUOTE]
> 
> The thing with a "tune pipe" is that it's "tune" for a specific aplication
> example: low end torque= longer heather smaller diffuser
> ...


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## Rivergypsy (Feb 26, 2013)

For a production 90deg V there's always the RGV250 - much fun, and two separate cases ;o)


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## wildun (Feb 26, 2013)

This is more than enough for starting and real power from two strokes come from the tuned exhaust pipes anyway.
 in meantime enjoy a picture of worlds most best single cylinder motorbike.
 
Kind regards
 
Niels[/QUOTE said:
			
		

> NIELS
> I agree, MZ (and Walter Kaaden in particular) is the company which contributed most to the development of the two stroke engine even though it was kept constrained by the Communist regeime in East Germany) and only when the young Ernst Degner, who raced their motorcycles defected to Japan and conveniently took all the designs with him to Suzuki, did his work start to blossom.
> The others soon started to copy them and it was all on during the sixties and seventies with phenomenal power outputs being realised, but the environmentalists eventually saw to it that it was stopped in its tracks ( I guess we had to make more room in the atmosphere for for the soot from jet aircraft and factories!).
> Now we are back to the four strokes which are complicated bulky and heavy (and expensive) - but don't get me wrong, still great nevertheless.
> ...


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## ShedBoy (Feb 26, 2013)

Not exactly a model but I am waiting to see this run
http://www.mwv2.com/creating-v16-victa-the-ultimate-useless/Page-3.html

This bloke has built some amazing engines. He has a common, LONG, crankcase which is pressurized by a small car supercharger. 

Brock


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## Paulsv (Feb 26, 2013)

I believe there are plans for a two cylinder 2-stroke in the downloads section of this site.  Here's a link:

http://www.homemodelenginemachinist.com/downloads/lobo-16-cc-twin-cylinder-2-stroke-diesel-161.html

It appears to use two separate crankcases.


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## ShedBoy (Feb 26, 2013)

Both pistons need to move up and down at the same time to achieve crankcase pumping and the smaller the volume of the crankcase the more efficient it will be.There is a plan available on the web. I have the pdf of it.
Brock


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## wildun (Feb 26, 2013)

ShedBoy said:


> Both pistons need to move up and down at the same time to achieve crankcase pumping
> Brock


 
SHEDBOY 
Yes I agree with that but as I should have said before, a two stroke V twin could use a common crankcase, but that would require seperate (staggered) crankpins, or two seperate (geared) cranks to allow simultaneously firing pistons. 
Using a common crankpin arrangement as in the classical four stroke V twin however - although it might run, won't be of much use unless you use some sort of blower arrangement. 

Please forgive me if someone else has said the same thing!

I would like to see the PDF you mention.


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## ShedBoy (Feb 27, 2013)

wildun said:


> SHEDBOY
> 
> I would like to see the PDF you mention.


  PM sent

Brock


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## Gedeon Spilett (Feb 27, 2013)

hi 
have a look at this one too, from my "to do" list, an old timer 2 strokes (spark ignition !) 2 cylinders in line, as 2 independent engines.
the pdf for the complete blue prints and instructions build (in french) is here
http://ti1ca.com/jumac77l-bicylindres-Sablier2-bicylindres-Sablier2.pdf.html

18 mm bore & stroke, a decent size, cheap and not that difficult to make IMO
cheers


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## lohring (Feb 27, 2013)

Below are a couple pictures of the Aprilia 250 V twin.  It's two 125 cylinder engines with their own crankshafts geared together.  Their 125 is considered to be the most highly developed simple two stroke so far.

Lohring Miller


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## Niels Abildgaard (Feb 27, 2013)

Have always dreamed of better mousetraps and light sport aircraft engines.Let me try to scheme the ultimate Rotax 912 beater.
We need about 60 horsepower and the prop shall turn  not more than 2400 rpm to avoid to much noise.
To find the nessecary two stroke volume (Fourstrokes are undelicious) i have used the formula 

Moving effective pressure (bars)
          times
Volume (litres)
           times 
working beats per second

  will equal 

horsepower
   times
7,5

Mep for crankcase scavenging can be 5 and for very mild turbocharging 10
(Normal fourstrokes can be 8 to10 but do not merit consideration among decent people.)
Let me asume 10 bar Mep and 40 rounds per second and target 60 horsepower
This gives 570 ccm per cylinder for my inversed 90 degree V2.
A stroke of 120 mm gives a mean piston speed of 10 meter per second and thats where piston engines run best.
Bore is thus 78 let us say 80 mm.
Pistons are not really good for controling exhaust.They go unround and may loose temper.Valves are much better.
A 2400 rpm two stroke exhaust valve behaves like a 4800 fourstroke and can be pushrod.
WW1 or 2 directcoupled aircraftengines were about 16 to 22 kg mass per littre so can be  very competitive here.
It is now time for drawing


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## dman (Feb 27, 2013)

wildun said:


> Using a common crankpin arrangement as in the classical four stroke V twin however - although it might run, won't be of much use unless you use some sort of blower arrangement.



i hope not to start a flame war but what makes you believe this? i'm actually liking the idea of a common crank pin v twin, or better a v4. why use a common pin? well i don't see the point in a v2 if the cylinders are phased the same. may as well make a boxer or big single. 

a common pin twin may need more timing and more tuning of port angles and may idle unevenly but by my quick math, not considering the rod:stroke ratio the displaced lower end volume is about .707x the total volume of the two cylinders. once you factor in port height that should be enough to evacuate the exhaust from the cylinders but it may need a little more timing than a single cylinder and it may be more sensitive to port angles.


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## petertha (Feb 27, 2013)

dman said:


> 3. super charging....usually positive displacement type with a displacement a bit more than the combined cylinder volume. vane style is popular for models and roots is used on full size engines... a centrifugal may work on full scale but on model scale I doubt it (centrifugal chargers don't scale nice and are harder to engineer because they have a pressure per tip velocity relationship rather than a volume per revolution relationship.) super charing has been done on model radial engines


 
dman, I am going to start a new inquiry post specifically related to SC/boost for model radials, so I don't want to derail this 2-stroke post. 

But in the meantime, can you provide any links or references to your reference "vane style is popular for models". I'd be interested to see details of what work has been done on models, how much boost they provide, how they are constructed etc.

I've seen pics of the Hodgson 'centrifugal device' applied to his radials. (I've callled it device as I'm not sure its a centrifugal SC. Ive heard it called a combination mild booster / flow disperser, but I'm not qualified to say in any event).

whirlywheel construction & assembly near bottom of build pics
http://picasaweb.google.com/18.cyl.radial.engine/HodgsonRadial18#5293775425552828066

cad sketch under crankshaft assembly
http://thebloughs.net/hobbies/metalworking/hodgson9/


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## Niels Abildgaard (Feb 27, 2013)

Blower Charged Two Stroke Engines
Model engineer 1971 issue 34(12 13 14)
M.Hollick


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## dman (Feb 27, 2013)

petertha said:


> dman, I am going to start a new inquiry post specifically related to SC/boost for model radials, so I don't want to derail this 2-stroke post.
> 
> But in the meantime, can you provide any links or references to your reference "vane style is popular for models". I'd be interested to see details of what work has been done on models, how much boost they provide, how they are constructed etc.
> 
> ...



 i'm not sure i can say it's popular. maybe that was inaccurate, it's not as common to see radial 2 strokes for the reasons of it needing a supercharger so i can only say ive seen a couple examples. but i've seen it, it's a logical way to go because it fits nicely on the back of the crankcase and is easy to build. 

radial 2 strok plans

also note the super charger doesn't produce boost it's just an air pump, conventional wisdom is that it needs to displace 1.3-1.5x the volume of the cylinders above the exhaust port. boost can't happen on a 2 stroke untill the exhaust starts working. on a typical 2 stroke the exhaust port has more timing than the intake so blowing more into it just pushes more out the exhaust. once the exhaust starts working there is a designed in reflection and/or pendulum effect that provide reversion after the cylinder is over scavenged (so the reversion is unburned fuel/air mixture) and can raise the cylinder pressure which is why the exhaust needs to be timed wider than the intake.


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## Jordan (Feb 27, 2013)

Not a Freak!
An interesting early V twin 2 stroke engine is at the Sammy Miller Museum in England.
Search for images in Google etc.
A brochure can be seen here: http://reddevilmotors.blogspot.com.au/2012/06/stanger-two-stroke-v-twin-1919.html
It has two separate crank chambers.
I think it could be possible to have a common chamber on a V twin, if the crankpins were staggered so the pistons went up and down in unison?
My wife made me sell my MZ - she said it was ugly!
Jordan


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## petertha (Feb 27, 2013)

Niels Abildgaard said:


> Blower Charged Two Stroke Engines
> Model engineer 1971 issue 34(12 13 14)
> M.Hollick


 
Now how am I going to get my hands on those magazine articles?


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## Niels Abildgaard (Feb 28, 2013)

Jordan said:


> Not a Freak!
> An interesting early V twin 2 stroke engine is at the Sammy Miller Museum in England.
> Search for images in Google etc.
> A brochure can be seen here: http://reddevilmotors.blogspot.com.au/2012/06/stanger-two-stroke-v-twin-1919.html
> ...



Hello Jordan 

Can we old men have a picture of Mz and wife and let us judge if You choosed wisely?

Regards

Niels


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## wildun (Feb 28, 2013)

dman said:


> i hope not to start a flame war but what makes you believe this? i'm actually liking the idea of a common crank pin v twin, or better a v4. why use a common pin? well i don't see the point in a v2 if the cylinders are phased the same. may as well make a boxer or big single.
> .


 
Sorry Dman,
I have just seen your post so I have to sit here a while and digest it all and if I can't come up with a logical answer, then I'll tell you that I can't!:rant:


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## wildun (Feb 28, 2013)

Niels Abildgaard said:


> .
> Pistons are not really good for controling exhaust.They go unround and may loose temper.Valves are much better.
> A 2400 rpm two stroke exhaust valve behaves like a 4800 fourstroke and can be pushrod.
> It is now time for drawing


 
Niels,
An italian company in the seventies built a kart engine with DOHC, (and I mean DOHC TWO STROKE, from memory the camshafts went at half crank speed, the valves opening alternately (keeping them from over doing things at high revs)  - maybe not a great idea for a racing Go Kart because it disappeared quickly from the scene! but maybe quite a good idea for a light aircraft engine however, - possibly less piston seizures.

Now I have to sit down and figure out Dman's theories! - maybe he's trying to wind me up!


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## mikegw1961 (Feb 28, 2013)

Petertha

Old model engineer magazines are available on eBay

Normally they are about £4.00 / copy
I have just got 5 old issues for £19.95

Mike


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## wildun (Feb 28, 2013)

dman said:


> i hope not to start a flame war but what makes you believe this? i'm actually liking the idea of a common crank pin v twin, or better a v4. why use a common pin? well i don't see the point in a v2 if the cylinders are phased the same. may as well make a boxer or big single.
> 
> a common pin twin may need more timing and more tuning of port angles and may idle unevenly but by my quick math, not considering the rod:stroke ratio the displaced lower end volume is about .707x the total volume of the two cylinders. once you factor in port height that should be enough to evacuate the exhaust from the cylinders but it may need a little more timing than a single cylinder and it may be more sensitive to port angles.


 
Dman, 
don't worry about a flame war, I have a hide like a Rhino and I do like to -shall we say 'debate things' but I will concede defeat if I see that you are talking from an enlightened perspective!
As I see it, (and you may have a bit of a jump on me from the point of view of sitting down and nutting it out) and I did mention earlier that it would work - possibly not well, but i think it all boils down to the application it is to be used for, - eg is it to sit on a wooden plinth and burble along looking pretty, just to prove that it will run? or is it going to produce some useful horsepower with sophisticated computer designed expansion chambers laboriously welded together, (or perhaps done by robot welder), - Gordon Jennings would turn in his grave if he heard you!

Truth is mate, I don't know, I haven't looked at this stuff for about 30 years, but my advice is, "suck it and see" - more stuff has been designed by trial and error, educated guesses and doing outrageous things in the past, than many people would ever admit!


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## wildun (Feb 28, 2013)

dman said:


> "i hope not to start a flame war but what makes you believe this? i'm actually liking the idea of a common crank pin v twin, or better a v4. why use a common pin? well i don't see the point in a v2 if the cylinders are phased the same. may as well make a boxer or big single."]
> 
> That would just be a matter of preference I guess - maybe a boxer or big single would have nicer sound or better looks, - but no doubt there is some very good reason why a common pin 'V' arrangement is never seen in use on a two stroke, so you should perhaps try it and find out why.
> The 'V' angle will have a big effect on your volume calculations too, - I was envisaging a 90 deg. angle but a much smaller V angle would be getting closer to single cylinder territory.
> ...


 
Not sure what you mean by "more timing" - to me that means longer duration, ie. earlier opening and later closing? - (depends on where we come from I guess!).
That I think it would be extremely difficult to calculate and it will depend very much on the design of the exhaust chamber. There will need to be a huge amount of trial and error experimentation to get it right!

By "port angles", do you mean in a directional sense or crank angles/port timing?

And some people think that the two stroke engine is simple!

BTW, - Not saying you are wrong at all,- no contest! - just trying to get my head around the concept by bringing some points, which I consider to be valid into the discussion and I would like your comments.


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## Niels Abildgaard (Feb 28, 2013)

A 90 degree 60 horsepower/2400 rpm aircraft engine .
80 mm bore and 120 stroke.
Mass as shown (uncut cylinder units) 16 kg.


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## dman (Feb 28, 2013)

wildun said:


> Not sure what you mean by "more timing" - to me that means longer duration, ie. earlier opening and later closing? - (depends on where we come from I guess!).
> That I think it would be extremely difficult to calculate and it will depend very much on the design of the exhaust chamber. There will need to be a huge amount of trial and error experimentation to get it right!
> 
> By "port angles", do you mean in a directional sense or crank angles/port timing?
> ...



well "more timing" is just an idea i had of how you'd deal with 29.3% less pumping volume. the ratio of the crankcase displacement and the compressed volume has everything to do with the port height which also controls the timing. but it might not matter. the idea of having a surplus of pumping volume might just be because it was inherent to the single cylinder design and worked. i think with some time put into flow patterns you may be able to get closer to 1:1 pumping volume to compression volume and have it run good. 

there would also need to be time put into examining how you'd deal with the pumping being out of phase from the cylinders. it would trail one and lead the other. and there would be overlap with the pistons at different heights and different rates of flow so restriction on one cylinder may over fill the other. i think it could be done but it would take time with a physics simulator or a lot of thought and some experimentation or all 3.  

most of my theoretical and applied knowledge is with american v-8 racing engines. so i'm delving into mostly theory here. i used to play with 2 strokes but mostly just as rebuilds and maintenance. not so much designing exhaust or altering timing. 

this is as far as i want to go into this on this thread. maybe a new thread could be started on the ideas of v-twin 2 strokes and what's best, seperate crank pins and timed together, sperate crank case areas and timed 180 apart, or single pin, single crank case. they all have points. the single pin would be the biggest engineering nightmare but would balance well and be small and light and although odd fire would be smoother than a single. the 2 pin 1 crankcase would be simple to design and be light but with both pistons having the same firing angle it's kinda like just having one piston. and separate crank cases would have even firing and no design problems but adds a bit more weight though that wouldn't matter much at all. i admit a common pin v twin 2 stroke is messy. i wouldn't expect it to be considered a good idea but i kinda want to try it.


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## wildun (Feb 28, 2013)

Niels,
How many exhaust valves per cylinder? -  pushrod? - normally aspirated as per Dman's recipie?
I can see that the OHV design will allow shorter piston skirts and I guess this will  compensate for the longer stroke.  - I see you are going for torque.   
Looking forward to watching it progress.


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## wildun (Feb 28, 2013)

dman said:


> i admit a common pin v twin 2 stroke is messy. i wouldn't expect it to be considered a good idea but i kinda want to try it.


 
Dman, 
Yes, but I would be inclined to give it a go, can't do any harm. - you are probably way more qualified than I am, - these days I tend to work more on hunches and maybe the odd educated guess, I probably would be capable of working it out on paper, but I'm just too lazy now!
 I'm afraid my engineering ambitions are a bit limited since moving to a smaller home, and then there's the age thing..........just excuses I guess! - waiting  to see what Niels is planning!
Thanks for the discussion


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## Jordan (Mar 2, 2013)

My wife made me sell my MZ - she said it was ugly!
Jordan



Niels Abildgaard said:


> Can we old men have a picture of Mz and wife and let us judge if You choosed wisely?



They both look good to me. Maybe she was jealous?

Jordan


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## WCPenney (Mar 4, 2013)

The outboard motor manufacturers have had multi-cylinder two stroke design nailed for quite some time. You guys have me scratching my head as to how my 225hp v6 two stroke is put together now. I haven't looked at it in ages (in storage.) I do remember that it's a flathead and I think it had 6 barrels...


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