Elaborating along this previous question, could you please invalidate this ICE design with solid authoritative arguments explaining all the flaws?

Starting hypothesis:

Whatever the purpose, one single large coaxial valve is better at effortlessly filling or emptying one cylinder, compared to 2, 3, 4, or 5 valves per cylinder's head.

For a four stroke cycle ICE to work it requires a system that involves (or replicates the behavior of*) at least two valves, intake and exhaust.

If maximum cylinder head's surface is occupied by one (exhaust) valve**, the other (intake) valve could be embedded in the piston.

Maybe a better filling/emptying performance can outbalance a complex internal valve design.


Conceptual animation, please imagine a gear train of five smaller gears instead of three, in sandwich between bipartite connecting rod, so that they don't collide with anything.

Notice the natural variable opening and closing speed of the intake valve due to combined motion of the whole system around crankshaft's pin. (closes faster than it opens, (cam rotates contrarotative to crankshaft)

Intake valve does not need a counterweight to balance itself as it is meant to be either locked closed, or its opening/closing is helped by inertia, still the whole piston-valve-connecting rod system has to be balanced with a crankshaft counterweight. (all of this missing in the animated gif below)




*ports at the bottom of the sleeve / sleeve valve (bristol-like)

**spark plug somewhere

  • 1
    $\begingroup$ Issues of balancing the reciprocating mass. $\endgroup$
    – Solar Mike
    Oct 16, 2022 at 19:37
  • 1
    $\begingroup$ Gears magically penetrating the cylinder walls. $\endgroup$
    – DKNguyen
    Oct 16, 2022 at 19:40
  • 1
    $\begingroup$ Wouldn't all the oil spraying and driping around above the sump get drawn into the combustion chamber? Would positive pressure be required in the sump? Would that force fuel-air mix up through the oilways? $\endgroup$
    – Transistor
    Oct 16, 2022 at 20:26
  • $\begingroup$ @Transistor those are good points I have no clue about, designing this I was thinking about oil mixed with fuel, like for 2 stroke gasoline engines or glow plug methanol $\endgroup$
    – user12750
    Oct 16, 2022 at 20:35
  • $\begingroup$ Instead of lifting the valve, rotate it so that ports open. The gear train can be fixed that way. It's called a rotary sleeve engine, and it eventually was proven to be heavier and had no real compensating advantages. enginehistory.org/members/articles/Sleeve.pdf $\endgroup$
    – Phil Sweet
    Oct 16, 2022 at 20:55

1 Answer 1


Your initial starting hypothesis is wrong. One large valve has high inertia and is thus unsuitable for high speed reciprocal action. High engine speed is how we get high power. This is why twin cam 4-valve cylinders are a thing. There are solutions already in place for slow-moving engines, they are the large 2-stroke marine engines. Judging from the size of your valves, you recognize that the limitation for a spark-ignition engine is getting air into it. The problem is you won't be able to cycle all that mass fast enough for it to matter. A small valve works fine for slow speeds.

Next, your valve-in-a-piston thing seems needlessly complex, especially given your error in hypothesis 1. And you have added more reciprocting mass. And you'll have to lubricate all those extra journals you created for your new gears.

You haven't done anything to improve filling performance. Engines already have variable valve timing. If your speed-based solution makes sense, go apply it to a regular valve train.

Last is passing everything through the crankcase is terrible. No way to get good tuned inlet passages when air is everywhere in the crankcase. And you're adding fuel to the crankcase? Oh the carnage of those new journals! Plus don't expect emissions approval from an oil-burner.

  • $\begingroup$ that makes sense, all of your points, mostly for the wrong hypothesis about cylinder filling greater performance of one vs. 2,3,4 valvaes. what I had in mind was something along 10cc displacement with very long stroke. tyvm $\endgroup$
    – user12750
    Oct 18, 2022 at 8:08

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