Interesting engine designs

Here is an interesting engine design that I havn’t seen before.


I want to see how they bore a curved cylinder. I can’t figure it out.


Imagine a rotating boring head in a vertical mill. Then the block is rotated, upward, on the same pivot shaft that the curved piston arm will rotate on.


I’m trying to visualize it Rindert, but the bottom back edge of the cutter hits first and then the front face of the cutter contacts the bore and the hole seems to come out oval.


But the piston will follow exactly the same path that the cutter did, so the piston rings will see a circles, not an ovals. This is why the piston rings are canted to each other. Each piston ring can then see it’s own circular bore.
P.S. I can’t quite imagine the honing process yet, though I’m sure there’s a way.


Rindert, Yes, you got it. A thin washer-shaped cutting tool that follows the exact path of the piston. A hone would look about the same with grinding compound instead of a cutter. the information about the inventor talked about production of precision compressors used for medical / scientific gasses built with the pendulum piston that were able to use Teflon piston rings because the motion is so stable. This is a neat concept, that seems to be under-studied. I can see potential problems with high RPM operation, but maybe not if the moving parts are kept very light. :cowboy_hat_face:


Strength to density ratio dictates that aluminum pistons are used. This will hold true for pendulum engines also. The max theoretical speed for reciprocating engines is ~20,000 rpm. A few very small model engines approach this.


Thanks for the drawing Rindert. I can see it now. I was thinking of a different kind of cutter head.


AS far as i know it is RPM is limited by the piston speed that is why we went to short stroke engines .so the piston has to travel less distance , This engine would still be governed by that as it is the starting and stopping at the end of each stroke that creates the stresses


I’m looking for any advantages to this complicated to make engine. Other than piston side thrust management I’m not seeing any. As for how to hone the cylinder - I presume a ball or “flex-hone” hone was used.

another interesting design


The Commer Knocker had good power to weight ratio. Perhaps good for aircraft.

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Thanks for the Taurozzi engine link DonM. One I had never seen before.

Here are my contributions to “better-IC-engines”.
My working engines repair, restoration and maintenances experiences says, the simpler, the better. And the better manufactured is the best of all. Here is a new running loaded comparison of these principles:

All four the same best contemporary workhouse design. WHO manufactures them; deciding what materials, what manufacturing tolerances make determines as much the success, or premature failure as the Idealism of a base design.

And a design can only rise to wide usages if it has good collaboration work at the design level. With the wiliness to do 180-degree turnarounds, yet still have follow through problems endurances. And then a partnership with $$$$$$$$$ backers:

Honda has been working quite long now a on small single cylinder true Atkinson multi-link piston to crankshaft engine for use in their stationary small powerplant applications. They promote the longer power expansion cycle as the prime benefit. They have yet in extended testing to get the same service life out of all of those lower crankcase pivots and bearings as a conventional design.

My last Dealership job as their Used car Tech I worked first on a 1st Generation Honda Passport (a rebranded Isuzu) with noisy valve train and leaking V-6 cam covers. O.K. Teardown to reseal the cast valve covers. Single overhead camshafts valve design, hemi-head. Isuzu used an offset of center camshaft. And thru a set of shaft mounted rocker arms actuated one set of valves. Straightforward. But get this . . . the other valves were operated by two shaft mounted transfer rocker arms; one to the other, to get the distance over. So . . . every rocker arm end pad, and center shaft pivot had rubbing wear. No adjustments. No fix for the Clickety. Clackety. Clickety.
Then the same reseal cams covers job on a three years newer Honda (Izuzu) Passport. They had simplified to a central mounted single camshaft with single side rocker arms and adding the mini oil-hydraulic lash adjusters. Only clickety, clickety when cold warming up, untill getting enough oil to the lash adjusters. Both were 150k-plus miles vehicle with obvious good oil changes.

Nothing simpler that a crankcase pressurizing, piston-port 2-stroke. Being killed off not just by measured exhaust emissions but the make illegal to manufacture or sell ANY intentional oil-loss engine into civilized areas of the world.
Almost as simple is an Otto four-stroke valves-in-block engine. Easy, easy to manufacture. Easy to internally oil all wearing points. But terrible combustion characteristics. PITA to service those valves too.
Overhead camshafts designs are very oil pressure and flow dependent. Then a lot of design to keep all of that needed upper end pumped up and drain back oil from drowning the valve stems. Become smoker engines with valve seals wear.
All in all the overhead valves actuated by an in-block cam with pushrods and rocker arms is imho the best compromise between too-simple, and too-bragging-complex.

Already preparing the Wife who just will not quit for her next new; travel-too, in-home Nursemobile vehicle.
It will either be a Mazda with a Skyactive-G or X, Miller cycle.
Or a Hyundia electric motorized camshaft emulated Atkinson cycle.
Reward those production manufacturers still developing and making IC piston engines.
(Ha! Three times now in 25 years I’ve struck out getting her to go Toyota . . . not going to spit into that wind again.)

The War Against the Carbons Polluting, IC Piston Engines still has some kicks and bites, and purchase votes left.
Steve Unruh


Steve, you are good at bringing back memories. One of my grandpa’s favorite sayings was:

As you go through life, two rules never bend
Never whittle towards yourself, or pee against the wind

Garry C


And then sometimes the next-gen step-forward engine is just adding more cylinders:


I’ve seen compressors with that design and no issues very low maintenance

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