# Twingle engine



## nx06563 (Jul 26, 2019)

I am looking for  a new model to start building and in my search for plans I came across an engine called a "Twingle" which is evidently a split single design.
Does anybody have plans for a split single engine or have one that is running.

I would like to know more about them and would love to have a set of plans to build one

Thanks
Hogan


----------



## stevehuckss396 (Jul 26, 2019)

I have been cruising the model engine scene for a long time and have never heard of a scaled down twingle. Yours may be the first.


----------



## vederstein (Jul 27, 2019)

I didn't know what a Twingle was so I did a little bit of searching.  Two cylinders acting as a single cylinder.

There's got to be a good reason for this.  Why would a manufacturer do this, especially when the strokes aren't much different?

...Ved.


----------



## WOB (Jul 27, 2019)

The reason it was developed was to improve mixture flow from the crankcase into the combustion chamber, minimize plug fouling,  and  improve exhaust scavenging.  The principle is fully explained in the Wikipedia article here: https://en.wikipedia.org/wiki/Split-single

WOB


----------



## nx06563 (Jul 28, 2019)

Sounds like there were several motorcycle  engines that used this principle.  Who am I to judge?  Sounds like a neat build though.  I did find an article by R.E. Mitchell with a title " A Split Single Two Stroke Engine"   with a sub title of "An effecient unit for propelling a class C Hydroplane.
In my younger years I raced pro outboards in APBA sanctioned events. The classes when I first started racing were A,B,C,D,and F  based on engine displacement. I raced with a gentleman that had raced since the 1940's who knew all there was to know about boat racing and I never heard of him talk of a Split Single.
 The article refers to MPBA regattas.  The gist of which sounds like teather car racing with model boats.  Is anyone familiar with such a thing.  The history would be fun to learn.
Guess my next Google search will be MPBA

Thanks for helping the search.
Hogan


----------



## nx06563 (Jul 28, 2019)

My goodness what google can find.  It is teather boat and rc boat racing.  Looks like the real thing I used to do but at 1/10th scale. It is a UK sport and it looks like a bunch of kooks like model engine builders. Now I am encouraged to find a model engine plan.


----------



## BWMSBLDR1 (Jul 29, 2019)

stevehuckss396 said:


> I have been cruising the model engine scene for a long time and have never heard of a scaled down twingle. Yours may be the first.


The most common model of "Twingle" two stroke engines were the Allstate 175 and 250 cc motorcycles sold by Sears in the late 50's. Built by Steyr Pusch in Austria they were torquey but low revving bikes with good reliability. Just outclassed by the Japanese bikes of the 60's.
At the other end of the spectrum is the DKW 500 cc racer from the 30's. A twingle with a third "pumping" piston to increase air flow through the engine it gobbled fuel (alcohol, nitromethane, and ???), made lots of power and held it's own against BMW twins and the Norton singles in the FIM Grand Prix races! A marvel of engineering!  Bill in Boulder CO


----------



## Mago (Jul 29, 2019)

Twingle or Split single.

At the end of WW2 Triumph Motor cycles produced a 500cc split single called a "Speed Twin".
It was produced in several guises and with factory add ons was used for road racing.
In the right hands it was very competitive with factory single cylinder racers until the class was swamped with Italian multi cylinder machines and then by the Japanese.
British Triumph motor cycles have all disappeared.
My friend and fellow modeller has made three one third replicas of the engine.
He dismantled a full size engine and made drawings etc before manufacture from the solid.
Don't ask about availability of drawings, there are none.
Hope the photos inspire.

Mago


----------



## davidyat (Jul 30, 2019)

I seem to remember Puch making a 2 stroke engine that used 1 rod and 2 pistons with a common combustion chamber. The rod was shaped like a Y with the bottom of the Y connected to the crank and the top having the 2 pistons. At TDC, there was a passage between the 2 cylinders so they would have the same pressure. Not sure if this picture is the engine I'm thinking about but at least you see the common combustion chamber.
Grasshopper


----------



## davidyat (Jul 30, 2019)

I found the picture I was thinking about:


----------



## Michael Dobson (Jul 31, 2019)

Yes the cross section drawing is definitely a split single. Not sure if this one is a Puch but the principle using a forked connecting rod allows the relevant timing for scavenging and exhaust to help with strong torque at low revs.
The Triumph Speed Twin in the previous post however is definitely not a split single. That is a standard two cylinder four stroke with 360 degree crankpins spacing on the crankshaft. Nothing revolutionary there except for the fact that it set a trend in the motorcycle industry and was followed by lots of other manufacturers following suit.
The Triumph company (then) culminated in the last Bonneville 750 engines of the early 80s before the company folded. Triumph was reborn in 1991 under new management and a new factory with new designs. They made a completely new version of the Bonneville 360 degree twin (1998) and many more variants since.


----------



## davidyat (Jul 31, 2019)

I strongly believe the cut-away motorcycle engine in the picture is the same as the diagram below it. Look at how tall the pistons are in both pictures and if you look at the transfer ports in the photo, you see the height difference with the pistons that match the 3rd drawing. That would indicate that as the crank rotates, the tops of the Y would rock back and forth slightly and only be the same height at TDC and BDC.
Grasshopper


----------



## Michael Dobson (Jul 31, 2019)

Yes I'm sure you are correct. They were also made by Lucas, Garelli and a small car called Trojan.
Unusual 2 strokes are quite interesting, in fact I have been a making a model of a stepped piston twin, inspired by the Norton Wulf bike engine of the 70s. 
My point was about the Triumph, that's just a 4 stroke twin.


----------



## nx06563 (Aug 4, 2019)

Mago,  The engines you and your friend have built are way out of my league.  I am not quite that good of craftsman yet and don't really understand the design concepts of a 2 cycle (port design).  I think I will work on designing a twingle as my career ending project. as a model engineer. ( till I get too frustrated  )

Thanks for the pictures. you have done some awsome work.

Hogan


----------



## Tim Wescott (Dec 2, 2020)

I'm _really_ late to the party (actually I was looking for Twingle plans on the web and found this). What may not be apparent in the drawing is that a single, rocking connecting rod will bind if the attachment to crank and wrist pins is perfectly rigid.  That's because the paths described by the two rod ends are not perfectly parallel.  The three solutions that I know of are to hinge the connecting rods or run two rods on one pin, to make the rod flexible (this is what the Trojan did -- it had a long spindly rod that intentionally flexed), or to let one wrist pin float a bit laterally, either in the piston or in the rod end.

I'm pretty sure the Pugh did the floating wrist pin thing, because (A) I remember reading it on Wikipedia, and (B) there's no way a rod as rigid as is implied in that drawing could possibly not cause problems.


----------



## nx06563 (Dec 15, 2020)

finally got around to starting to work on designing a twingle.  I was googling to find out crank timing for the two pistons and came across a complete design.  In an earlier post I mentioned plans for a class c tether boat engine which I was going to use for a basis for my work.  
I came across a project to do a solid works design of that very engine by Verby Engineering.  Google "Solid Works Split Single Two Stroke engine model" and you should find it.
This is a project by a young mechanical engineering student at the University of Idaho. Sounds like a very smart young man.  Gosh I wish I was young again.


----------



## Tim Wescott (Dec 16, 2020)

I think different engines had different crank timings -- it's part of the charm.

I also think that engine has lots and lots of very little very fussy parts.  I'm pretty sure I'm not a good enough machinist to even think about building that!


----------



## Kasey (Feb 3, 2021)

Michael Dobson said:


> Yes I'm sure you are correct. They were also made by Lucas, Garelli and a small car called Trojan.
> Unusual 2 strokes are quite interesting, in fact I have been a making a model of a stepped piston twin, inspired by the Norton Wulf bike engine of the 70s.
> My point was about the Triumph, that's just a 4 stroke twin.
> [/QU
> Three years down the track, I'm now finishing a split single engine based on a victa twin mower engine. ..to be eventually a flat four. As a twin first to master the concept, and add another 2 cylinder block later. It seems an enginedesign put in the too hard basket. It may have great possibilities still unexplored....even to revive two stroke engines with full lubrication? Or in combination with a 4 stroke and a rotary valve inlet head only? That part will be my next try after ths one.


----------



## Kasey (Feb 3, 2021)

Tim Wescott said:


> I'm _really_ late to the party (actually I was looking for Twingle plans on the web and found this). What may not be apparent in the drawing is that a single, rocking connecting rod will bind if the attachment to crank and wrist pins is perfectly rigid.  That's because the paths described by the two rod ends are not perfectly parallel.  The three solutions that I know of are to hinge the connecting rods or run two rods on one pin, to make the rod flexible (this is what the Trojan did -- it had a long spindly rod that intentionally flexed), or to let one wrist pin float a bit laterally, either in the piston or in the rod end.
> 
> I'm pretty sure the Pugh did the floating wrist pin thing, because (A) I remember reading it on Wikipedia, and (B) there's no way a rod as rigid as is implied in that drawing could possibly not cause problems.




Three years down the track, I'm now finishing a split single engine based on a victa twin mower engine. ..to be eventually a flat four. As a twin first to master the concept, and add another 2 cylinder block later. It seems an engine design put in the too hard basket. It may have great possibilities still unexplored....even to revive two stroke engines with full lubrication? Or in combination with a 4 stroke and a rotary valve inlet head only? That part will be my next try after thIs one.


----------



## TonyM (Feb 6, 2021)

Beautiful models Mago. Not a ''twingle'' as in the Puch design, Triumphs were 360 degree four stroke twins and although both pistons travelled up and down at exactly the same time they fired on alternate revolutions. 



Mago said:


> Twingle or Split single.
> 
> At the end of WW2 Triumph Motor cycles produced a 500cc split single called a "Speed Twin".
> It was produced in several guises and with factory add ons was used for road racing.
> ...


----------



## Kasey (Feb 7, 2021)

My next project once these flat  twin/ flat four "twingles' are_ up and running, is to build a single cylinder Victa engine with a rotary valve inlet head only, with a 2 stroke type exhaust, with an exhaust driven valve._


----------



## Kasey (Feb 8, 2021)

Here is a "naked" photo of the half "flat four" mounted for the first time on an old Victa base I'll use to test this "single" .....Once the other single block is cast and machined and fitted to make the flat four, I'll need to mount it via a different system, probably on an outboard leg in a test tank with air cooling fins added.


----------



## Richard Hed (Feb 9, 2021)

BWMSBLDR1 said:


> The most common model of "Twingle" two stroke engines were the Allstate 175 and 250 cc motorcycles sold by Sears in the late 50's. Built by Steyr Pusch in Austria they were torquey but low revving bikes with good reliability. Just outclassed by the Japanese bikes of the 60's.
> At the other end of the spectrum is the DKW 500 cc racer from the 30's. A twingle with a third "pumping" piston to increase air flow through the engine it gobbled fuel (alcohol, nitromethane, and ???), made lots of power and held it's own against BMW twins and the Norton singles in the FIM Grand Prix races! A marvel of engineering!  Bill in Boulder CO


That's really amazing as I never heard of the Allstate nor the DKW


----------



## Kasey (Feb 9, 2021)

Richard Hed said:


> That's really amazing as I never heard of the Allstate nor the DKW


In fact DKW were the large parent company to AUDI, the now famous German car maker......and one of those which made up the 4 ri_ng symbol for Auto Union, the actual name of the merged four companies_


----------

