Talk:Opposed-piston engine

What is an opposed piston design?
Andrewa I agree that opposed piston designs are 2-stroke (generally 2 stroke Diesel) but what you descripe doesn't seems to me an opposed piston design. I'm not sure about the technical name in English but it seems to be something like a Puch mortocycle engine : 2-stroke twin with a common combustion chamber. I simply can't imagine how such a design could work with an opposed design ? Ericd 18:55, 7 May 2004 (UTC)


 * The technical name in English is opposed piston. They work quite well, see the articles on Napier Deltic and Junkers Jumo 205. The Puch sounds like a similar design, perhaps you could contribute an article on it? Andrewa 03:32, 11 Nov 2004 (UTC)


 * Have a look at the diagram of a Garelli double-piston Puch engine at this website. It has two parallel pistons and a forked connecting-rod. This site also has a description of a later two-piston engine designed by Giovanni Marcellino, but with different sized pistons and a more elaborate connecting-rod setup, which seems to be the twingle engine described at this website.


 * Both engines were manufactured by Puch at their Graz works, the Marcellino design replacing the Garelli, and are described at the first site as one-cylinder double-piston two-stroke engines, but I'd describe them both as having two parallel cylinders sharing a single cylinder-head.


 * Anyway, neither seems to be an opposed-piston design. Could one of these be the engine you have in mind? Andrewa 19:07, 11 Nov 2004 (UTC)

Such engines are more correctly described as "U-cylinder" engines, as they have two cylinders in parallel sharing a common combustion chamber. — Preceding unsigned comment added by 5.70.203.120 (talk) 07:19, 20 August 2013 (UTC)


 * I've now done a stub on the Twingle engine. It seems to me this is what you are describing above. Andrewa 19:41, 11 Nov 2004 (UTC)


 * Puch double pistons engines are definitely not Opposed piston engines. Ericd 20:34, 6 October 2005 (UTC)


 * Beare Head opposed piston Sixstroke could also be considered as an opposed piston design. Malbeare 13:58, 15 July 2007 (UTC)

Stelzer engine
Removed text:

''==External links==

''*Stelzer engine schematic

This site does not describe an opposed piston engine. The designer appears to wish to use the term, but his engine does not seem to have been built or demonstrated, and until it is the existing engines surely have priority on the name. His intentions may be quite innocent, but a cynic would point out that the concept of the existing engines has been demonstrated to work, while the concept he calls opposed piston is completely different, and has not. Andrewa 03:32, 11 Nov 2004 (UTC)


 * The link is now offline. See also Talk:Stelzer engine. Andrewa 01:05, 6 October 2005 (UTC)

Intake and Exhaust in Fairbanks-Morse Engines
Paragraph 4 currently begins "Both the Jumo and Deltic engines used one piston per cylinder to expose an intake port, and the other to expose an exhaust port." This is also true of the F-M engines as described at the web page already referenced and at others, including U.S. Navy manuals for submarine engines (see pages 16 and 17 at this link http://www.maritime.org/fleetsub/diesel/chap1.htm#1C 7802mark 20:21, 25 May 2006 (UTC)

Inlet and exhaust cranks wrongly captioned?
Maybe I'm missing a point, but the captions for the inlet and exhaust crank mechanisms (no. 5 and 6 on the cutaway diagram) seem to be incorrectly labelled. --Slashme 08:01, 28 June 2006 (UTC)


 * The labelling is correct. The outlet piston opens (closes) the exhaust slots, the inlet piston is doing so with the inlet slots. The fuel-air mixture is flowing from (1) to (3), then trough the crankshaft housing to the inlet slots. But the outlet crankshaft housing is connected with the airbox, too. It is for cooling the piston bottom. UtzOnBike --85.179.167.210 21:40, 11 October 2006 (UTC)

Who is the R. Koreyvo (Kolomna Works)?
From which country Raymond Koreyvo came (Kolomna Works?) Is that Russia? Why hi patented his opposed piston diesel engine in France? Has anybody ever tried the concept before Junkers? —Preceding unsigned comment added by 86.147.234.117 (talk) 12:08, 10 September 2007 (UTC)

"Main Advantages" makes no sense
The "Main advantages" section of this article was letting the rest of it down. It read "The main advantages of the opposed piston design is efficiency. The fuel is burned inside the engine to expand gases to force pistons apart. In an engine with one cylinder head per piston, some heat from the fuel heats the piston head rather than expanding the gases to force pistons apart. This results in a loss of efficiency. The opposed piston Junkers Jumo 205 diesel was one example of this engine type." I'm not sure what the advantages were anyway, but this is not it. —Preceding unsigned comment added by MalcolmMcDonald (talk • contribs) 17:12, 24 December 2008 (UTC)


 * The advantage is simple: it's a good way to build a uniflow two-stroke compression-ignition (i.e. diesel with a small D) engine. There are no recent (1930s onwards) opposed piston engines that aren't. Opposed piston engines other than this are restricted to obscurities like the Gobron-Brille and some piston gas generator engines. Uniflow is the crucial factor here.


 * There may be weight advantages, but usually there aren't. For every Deltic, there's a Jumo 205.


 * Port timing asymmetry is valuable, but it's available (and more common) by using an exhaust valve as well as cylinder-ported inlets (or even sleeve valves). You don't need opposed pistons.


 * Thermal efficiency is a red herring. This is based on heat losses into the cylinder head being far more significant (in any piston engine) than losses into the cylinder walls. However an opposed piston doesn't avoid having a head, it merely uses another piston as one. This gives the same losses, and it loses that heat into a piston where it's difficult to dispose of it (c.f. the Deltic's many piston problems). Andy Dingley (talk) 12:27, 27 January 2010 (UTC)


 * Agree except large id uniflow engines have been made .One double acting with smaller secondary pistons and one crankshaft(B&W 1930ths)Wdl1961 (talk) 13:58, 27 January 2010 (UTC)


 * You mean that uniflow engines have been built that aren't opposed piston? Of course. That doesn't mean that opposed piston engines that aren't uniflows have been built recently. If you have an example, I'd be interested to know. Even the pretty early Junkers 2HK65 (a vertical with the upper pistons driven by a long yoke from the same crankshaft - 3 crankpins per cylinder!  ) was a uniflow. Andy Dingley (talk) 14:10, 27 January 2010 (UTC)


 * You found the Junkers ref i have been looking for ! Some opposed piston engines had larger id cylinders but i do not have english refs.Wdl1961 (talk) 15:02, 27 January 2010 (UTC)


 * Is the Junkers the one you meant? (the 1st photo, and engine, belong to an acquaintance) The pistons in that (and I would argue, any "opposed piston" engine) run in the same cylinder, thus are the same diameter.


 * The gas generator engines were both stepped piston and opposed, but those are really four pistons in two concentric cylinders. For a "pumping cylinder" two-stroke (illus.) the pump cylinders are bigger, but these aren't opposed. Andy Dingley (talk) 15:23, 27 January 2010 (UTC)

Interesting the junkers diameter was the same (except air pump) but the upper piston stroke was shorter than the bottom piston. Wdl1961 (talk) 15:46, 27 January 2010 (UTC)


 * It's a bit early (and slow) for them to be assuming Kadenacy effect, so I guess they were also failing to appreciate the importance of the scavenging airflow exceeding the swept volume. They might have been hoping that the extra air pump piston would have done some compression, but that seems optimistic. Andy Dingley (talk) 16:12, 27 January 2010 (UTC)

Nevertheless, an Advantages section is needed
Aside from one word ("efficiency") in the caption to a photo, there is no direct indication of the advantages and disadvantages of an opposed-piston design. The article would definitely benefit from such a section. — Preceding unsigned comment added by 98.231.177.64 (talk) 13:51, 8 October 2011 (UTC)
 * If I can piggy-back on this comment eight years later, why are/were they mainly used in large industrial applications? Why is it that apparently noone is making or using  them now?  Seems like the kind of thing that should be in the entry.  For example, the advantage of the wankel is it is small, light, makes a lot of power for its weight; the disadvantage it is inefficient in terms of fuel consumption, doesn't make power at low rpms, and tends to leak. There should at least be something like that for the opposed piston. 141.156.187.235 (talk) 03:48, 30 December 2019 (UTC)

External links modified
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What about boxer engines?
Should boxer engines be mentioned? Is a boxer engine the same as a horizontally arranged opposed-piston engine? If not, what is the difference? Joreberg (talk) 16:58, 2 June 2022 (UTC)


 * A boxer engine is a type of flat engine. See the animation at the top of that page, and compare it with the one at the top of this article. You should be able to see the difference. If that doesn't help, let me know, and I'll try to explain it. BilCat (talk) 05:28, 3 June 2022 (UTC)