"Split Single Cylinder" engine design ....

[Crazy Horse]

There is an off-road 4x4 "pickup" style vehicle currently on the Hemmings Auction Site for sale, the Austrian manufacturer Puch was one of the names on the nameplate. I remember that outfit selling motorcycles here in North American many years ago through Sears, a 250cc "twin" 2-stroke. But the twin only referred to the number of pistons, they shared a single common combustion chamber and one spark plug. You can see the animated visual below, pretty interesting. Not sure if this set up was ever used on their car and truck engines or how widespread the design was ever used elsewhere and by others. Apparently the big advantage over a normal 2-stroke was a more efficient scavenging of exhaust gases (which was always an issue with 2-stroke engines and contributed to their demise for the most part).

Operating princple​

Operating principle, with exhaust port left and intake right
The split-single uses a two-stroke cycle (i.e. where every downward stroke produces power) with the following phases:

1. Pistons travel upwards, compressing the fuel-air mixture in both cylinders. A spark plug ignites the mixture (in the right side cylinder in the animation) when the pistons are near the top of the cylinders.
2. Pressure from the ignited air-fuel mixture pushes both pistons downwards. Near the bottom of the travel, an exhaust port becomes exposed (at the rear of the left side cylinder in the animation), causing the exhaust gases to exit both cylinders.<a href="https://en.wikipedia.org/wiki/Split-single_engine#cite_note-Triumph_TWN-1"><span>[</span>1<span>]</span></a> At the same time, the intake port is exposed on the other cylinder, causing a fresh air-fuel mixture (which has been compressed in the crankcase by the downward movement of the pistons) to be drawn into the cylinder for the next cycle.

Characteristics​

 

[38 Sears Roebuck]

Very interesting, I haven't seen such an arrangement as that .

 

[Keith True]

I've had a few of those.They were called Twingles. They came in 175's and 250's. I liked the early ones because of the swoopy tin chassis design,with the bulbous tank and fenders.Later models had the toaster tank and small cycle fenders.Other guys liked the later ones for that reason.I sold a couple of parts bikes a few years ago,and if I bought one now it would be a complete bike,not a project one.Lots around,but they've gotten pricey.The pistons are two different sizes,and if I remember right they are inline,fore and aft on the bike.I really have no idea about the reasons for the design.Surprisingly enough,parts are readily available,from a place called West something,can't quite remember it.I still have two Allstate/Puch scooters,and get the parts from them.

 

[Bob Bancroft]

There is an off-road 4x4 "pickup" style vehicle currently on the Hemmings Auction Site for sale, the Austrian manufacturer Puch was one of the names on the nameplate. I remember that outfit selling motorcycles here in North American many years ago through Sears, a 250cc "twin" 2-stroke. But the twin only referred to the number of pistons, they shared a single common combustion chamber and one spark plug. You can see the animated visual below, pretty interesting. Not sure if this set up was ever used on their car and truck engines or how widespread the design was ever used elsewhere and by others. Apparently the big advantage over a normal 2-stroke was a more efficient scavenging of exhaust gases (which was always an issue with 2-stroke engines and contributed to their demise for the most part).

Operating princple​

Operating principle, with exhaust port left and intake right
The split-single uses a two-stroke cycle (i.e. where every downward stroke produces power) with the following phases:

1. Pistons travel upwards, compressing the fuel-air mixture in both cylinders. A spark plug ignites the mixture (in the right side cylinder in the animation) when the pistons are near the top of the cylinders.
2. Pressure from the ignited air-fuel mixture pushes both pistons downwards. Near the bottom of the travel, an exhaust port becomes exposed (at the rear of the left side cylinder in the animation), causing the exhaust gases to exit both cylinders.<a href="https://en.wikipedia.org/wiki/Split-single_engine#cite_note-Triumph_TWN-1"><span>[</span>1<span>]</span></a> At the same time, the intake port is exposed on the other cylinder, causing a fresh air-fuel mixture (which has been compressed in the crankcase by the downward movement of the pistons) to be drawn into the cylinder for the next cycle.

Characteristics​

Very interesting. So the downward motion of the pistons pressurizes the air in the crankcase such that a supercharger/blower isn't necessary? I suppose fuel could be injected up top rather than having to mix it going into the crankcase.

 

[Powered By IH]

There is an off-road 4x4 "pickup" style vehicle currently on the Hemmings Auction Site for sale, the Austrian manufacturer Puch was one of the names on the nameplate. I remember that outfit selling motorcycles here in North American many years ago through Sears, a 250cc "twin" 2-stroke. But the twin only referred to the number of pistons, they shared a single common combustion chamber and one spark plug. You can see the animated visual below, pretty interesting. Not sure if this set up was ever used on their car and truck engines or how widespread the design was ever used elsewhere and by others. Apparently the big advantage over a normal 2-stroke was a more efficient scavenging of exhaust gases (which was always an issue with 2-stroke engines and contributed to their demise for the most part).

Operating princple​

Operating principle, with exhaust port left and intake right
The split-single uses a two-stroke cycle (i.e. where every downward stroke produces power) with the following phases:

1. Pistons travel upwards, compressing the fuel-air mixture in both cylinders. A spark plug ignites the mixture (in the right side cylinder in the animation) when the pistons are near the top of the cylinders.
2. Pressure from the ignited air-fuel mixture pushes both pistons downwards. Near the bottom of the travel, an exhaust port becomes exposed (at the rear of the left side cylinder in the animation), causing the exhaust gases to exit both cylinders.<a href="https://en.wikipedia.org/wiki/Split-single_engine#cite_note-Triumph_TWN-1"><span>[</span>1<span>]</span></a> At the same time, the intake port is exposed on the other cylinder, causing a fresh air-fuel mixture (which has been compressed in the crankcase by the downward movement of the pistons) to be drawn into the cylinder for the next cycle.

Characteristics​

Wouldn't it work better with 2 spark plugs firing simultaneously?

 

[Bob Bancroft]

Wouldn't it work better with 2 spark plugs firing simultaneously?

I don't imagine we know exactly how it was arranged. Possibly they wanted the flame to travel a certain direction?

 

[Janicholson]

I had one (250) the crank was an articulated affair with one journal and a secondary rod grafted on above and to the rear for the rear cylinder. the smaller engine had a forked con rod. It was a slow RPM engine with lots of torque. More like a 4 stroke in feel. I did run reliably. Jim
link to images

 

[Keith True]

On the Twingle motorcycle it had two spark plugs,but one combustion chamber.One plug was on the rear of the head,the other one came straight out toward your left knee.They had actual dual exhaust,one pipe and muffler on each side.The carb bolted to a flange on the side of the jug,fairly high up.That dual exhaust with two big mufflers gave them a different sound,not the ring-ding of a Japanese 2-stroke.I'm thinking the 175 version had two different sized bores,and the 250 had the same size.What I never got used to was the kickstarter on the left side.My left side is too stupid to handle that.

 

[MarkB_MI]

Interesting. Here's a link to the full Wikipedia article.

Split-single engine

 

[Harold Hubbard]

Bob Bancroft:
Basic theory of most small 2cycle engines. That is why most of them use gasoline/oil mix for fuel. The oil in the mix lubricates the bearings on its way through the crankcase.