Quatrefoil epicyclic engine mechanism.

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
Dec 26, 2021
Reaction score
Kawerau, New Zealand
This motion is sort of like a 4-leaf clover.

I think it is a Celtic quatrefoil shape, which crosses in the centre.
A standard quatrefoil does not cross.

It would be suitable for an engine block that rotates, with the pistons moving in and out, but with a scotch linkage style motion.
This is similar to the X4 mechanism, in that separate piston rods are not used.
The motion can be generated as a 1:2 internal epitrochoid, only the outer ring rotates at half speed as well.
This makes a 4 stroke cycle similar to to a Wankel.
The downside is that the working cylinder volume is smaller than the outer chamber sweep volume.
I am trying to work out what type of connection there should be between the inner tooth ring gear and the centre orbiting gear, and the fixed block.
The inner tooth ring gear turns relative to the outer block, but does not orbit.
The smaller inner gear does orbit, so it can be on a half-stroke-length crank.
The outer ring gear is fixed to the inner rotating block.
I think the crank and the outer ring and the outer block need to be geared together so that any motion in one part will drive the other, relative to the outer block.
possibly a stepped gear with a bearing in the outer block, teeth on the outside of the outer ring gear, and a gear on the crank.
the outer ring has to go half the speed of the crank, so there is a gap to be filled by an idler.
The gear on the crankshaft should be half the diameter of the input gear, and rotate in the same direction.
thus the transfer shaft needs the same sized gear on each end.

If you want two pistons in the same bore, with opposite motion, would a secondary crank tied to the inner orbital gear, give the correct motion?
This would be a quatrefoil orbit 180 degrees out.
A forked piston bearing arrangement will balance the thrust forces on the pistons.
1) can the gear arrangement be simplified? there are 5 tooth sets at present.
2) is the cylinder swept volume worthwhile?
I would think that spring-loading the cylinders against the outer ring would give enough seal, with a curved shoe sector.
you would want inner and outer cylinders, where the outer cylinders act as guides, rather like a sleeve engine, but oil consumption can be less, as positive oil scraping can be used around each shoe.

I will add some diagrams.

The rotating piston linkage is a little difficult to make out, but I am fairly sure this is the correct epicyclic arrangement.

The big question with all these engine arrangements is: do any benefits outweigh any added complexity?
this looks like a workable scheme for peripheral porting, but I am adding extra gears.
Some of these gears would have to be specially made.
Would they need to be hardened and ground?- most likely- rather like gearbox gears.

The outer cranks would need to be overhung, and possibly geared together to keep them aligned.
A similar mechanism could use double-ended pistons, stacked in rows, eliminating the centre mini-cranks.
however, you then want a different valving system to feed the double-ended pistons.
A system using a single piston per bore and crossing the bores at right angles would work.
and possible the centre crank could be continuous.
You want a very light spinning centre block, though, to avoid excessive flywheel effect.

The barrel engine is better in that respect, with a high working volume to total spinning volume ratio.
Water cooling linkup to the stationary casing could be an issue. Maybe oil cooling is better in that case, with a common
wobble-plate sump.


  • Celtic Quatrefoil shape  18-02-22.jpg
    Celtic Quatrefoil shape 18-02-22.jpg
    236.5 KB · Views: 84
  • rotating piston linkage 18-02-22.jpg
    rotating piston linkage 18-02-22.jpg
    333.9 KB · Views: 70
  • celtic-heraldic-knot-bowen-symbol-true-lovers-knot-.jpg
    41 KB · Views: 72
Last edited:
1) the simple extra crank would not work to synchronise the 4 pistons.
2) I saw another mechanism somewhere that had 4 rods alongside the pistons, and 2 pistons in the same barrel, in a similar
I am not sure where that was, or how to find it again.
3) I wonder if the simple scotch linkage, short crank system out of the cross-four could be used.
I think this needs a gear to positively synchronise the pistons- does anyone know?
The mechanism I was thinking of is the Coaxial
Here are some images:
the Ma-250 also has an interesting mechanism.


  • coaxial 2.jpg
    coaxial 2.jpg
    44.6 KB · Views: 87
  • coaxial 3.jpg
    coaxial 3.jpg
    126.4 KB · Views: 91
  • Coaxial 4-rod mechanism engine.jpg
    Coaxial 4-rod mechanism engine.jpg
    32.1 KB · Views: 96
  • ma-250 engine 1.jpg
    ma-250 engine 1.jpg
    29.7 KB · Views: 96
  • ma-250 rotary valves.jpg
    ma-250 rotary valves.jpg
    47.8 KB · Views: 95
Fascinating - - - you might want to look into the quasi-turbine as another 'interesting' idea.
I prefer 4-stroke and round cylinders, thanks.
Something I might have a chance at building in a home workshop, out of conventional engine materials.
I think split-cycle cyclic engines are theoretically rather lossy.

That kind of thing is best done as a compressor-turbine layout, with a continuous burn.
This would be difficult to make reliable in a home workshop setting, and smaller ones are very inefficient.