Take a four-stroke bottom end, throw in a funky unconventional replacement for the cylinder head- something very similar to a two-stroke engine, and you have the six-stroke.
http://www.sixstroke.com/pageone.htm

"OK - what's it all about, Daddy Beare? "I began working 17 years ago on a stratified charge opposed-piston two-stroke design," recalls Malcolm, "but after building a couple of prototypes I realised flow control was a problem, with too many ports going everywhere. So I simplified (!) it into a six-stroke with the objective of improving efficiency and increasing performance compared to a conventional engine by overcoming the drawbacks of poppet valves, by means of a rotary valve application to four-stroke engine technology. I do have some engineering background, so I'd read widely about the various rotary valve designs aimed at overcoming the problems of poppet valves - inertia, inhibiting flow and especially the exhaust valve hot-spot in the combustion chamber. But while the Cross, Aspin and various other rotary valves were advantageous because they didn't restrict flow or absorb as much energy as poppet valves, they still had significant overheating problems of their own, with associated drawbacks in lubrication, oil and especially sealing. Of course, a two-stroke doesn't suffer such problems because it has no poppet valves - so I decided to try to resolve these drawbacks by taking the basic components of a rotary disc induction two-stroke engine, and grafting them on to a four-stroke to produce the best of both worlds. After a deal of work and experimenting since building my first six-stroke in 1990, I truly believe we've refined the concept, proved it's reliability and established it's worth, so now we have it fully patented - even in the USA - and ready for commercial use in the variety of applications it obviously lends itself to, including motorcycles, stationary engines and, because of the exceptional torque at low rpm, propeller aircraft engines."

HOW IT WORKS.

Gosh, could this bush-engineered Better Way perhaps be the mechanical equivalent of a Bimota Tesi or a Saxon Saxtrack/BMW alternative chassis concept for volume production? Well, let's see what it consists of.

Below the cylinder head gasket, everything is conventional, so one advantage is that the Beare concept can be transplanted on to existing engines without any need for redesigning or retooling the bottom end. But the cylinder head and its poppet valves gets thrown away. To replace the camshaft and valves, Beare has retained the cam drivebelt and fitted an ultra short-stroke upper crankshaft complete with piston, which the belt drives at half engine speed just as it previously drove the cam. This piston drives up and down in a sleeve, past inlet exhaust ports set into the cylinder wall, very much like on a two-stroke: these are all exposed during both inlet and exhaust strokes.

Continuing the two-stroke analogy, two 35mm Mikuni CV carbs mounted on each cylinder feed mixture into it via a reed-valve block, thus preventing exhaust gasses from escaping through the inlet. At the other end of the upper crankshaft is a two-stroke type rotary disc-valve that regulates timing, cutting off the exhaust flow at the appropriate time to stop the gasses returning into the cylinder, thus creating sub-atmospheric pressure during the inlet cycle. This being it's only function, the rotary valve is lightly loaded, reducing lubrication and sealing problems. It does need close tolerances though, which led to warping of the stainless steel disc Malcolm used on his first six-stroke, based on a Honda XL125 farm bike. Replacing the disc with a cast-iron one (on a Mk2 XT500-based version), cured this problem at the expense of extra weight. The Ducati uses hardened anodised aluminium discs, which work well.

During the compression and expansion strokes, the upper piston seals off both ports, leaving the pressure contained between the two pistons, with the lower one a conventional flat-top three-ring design, while the conical upper one (so shaped to aid gas flow during both inlet and exhaust cycles by guiding it towards the ports) has two rings - one compression, one oil. In the combustion phase, twin spark plugs provide ignition via the stock Ducati CDI and a pair of Harley coils - one per cylinder - and not only does the engine run on pure petrol (no need to add oil, because all required surfaces are positively lubricated, in spite of the application of two-stroke technology), it's also happy on low octane unleaded fuel. Obviously there are no valve seats to suffer from lack of lead, and Malcolm says the compression ratio can be increased significantly from the Ducati motor's 10.6:1 quite safely because of the lack of hotspots, without problems with detonation.

So now the claimed advantages of all this start to come to light - allowing a higher compression while still happy with low octane unleaded makes this an efficient and cleaner engine. There are no poppet valves to float or bend (OK, OK - I know this was once a Desmo, but this is a much more cost-effective way of achieving this than expensively machining a set of closing rockers for all the valves in a cylinder head, quite apart from the unwanted inertia such a system still entails) In turn, this implies a far higher safe rev limit for the six-stroke - 28,000rpm in theory, given the half-engine speed operation of the upper crankshaft, and the fact that GP reed-valve two-strokes peak at 14,000rpm. But Malcolm Beare says the rev limit, as on such two-strokes, depends only on what the main (conventional) crankshaft is able to bear, and he's arbitrarily limited the Ducati-based 6S-V2 to 9,000rpm for that reason, at which point he says (according to computer predictions) 86bhp is delivered at the rear wheel - there aren't too many dynojet rigs out in the Australian outback! Comparisons are hard to make, because of the difficulty of determining the exact cubic capacity of the 6S-V2's six-stroke engine: what began as an elderly Pantah V-twin now has a total 744cc's of compression/expansion volume, and 602cc of inlet/exhaust volume, and instead of absorbing about 10% of engine power in driving the camshafts, the cambelts now deliver about 9% net power to the main crankshaft after combustion via the upper, conical porting piston (see, desmo power!). But if you figure that a '97 model Ducati 900SS delivers 73bhp at the rear wheel in stock form, that's quite an impressive claimed power increase.

But there are other, much more significant apparent spin-off benefits from the Beare design. First of these is fuel economy: Malcolm Beare claims his engine is 35% more economical at low revs/throttle openings than an equivalent conventional engine and 13% less thirsty at high rpm/full throttle, in spite of the doubled-up carbs. That should mean fewer hydrocarbon and CO2 emissions, because you're using less fuel to achieve the same performance. Next there's improved torque at lower revs - on both his Yamaha and Ducati-based prototypes Beare discovered the six-stroke version produced the same torque as a four-stroke 1,000rpm lower down the scale, as well as producing exponentially more torque as revs rose. But in a commercial application, perhaps the most attractive benefit is the reduced number of moving parts, compared to a four-stroke design, so the six should be cheaper to make. Not as few as a two-stroke, but what you appear to be getting here is improved performance and torque, coupled with the inherent advantages of a four-stroke, on the cheap. Finally, as the upper two-stroke piston is driven at half engine speed, it should have twice the life of the lower four-stroke one. Sounds promising... "

 

sound file- I think he's constantly revving it because it sounds like it drops to a lower idle between revs, but I don't know for sure.
http://www.sixstroke.com/download/bike.wav

http://www.sixstroke.com/download/sixstroke.avi
Bigger verson of animation

 

that sounds wicked! I think that is the idle though...just MO..

 

I think it's a neat idea- not really an entirely different type of engine like a rotary, but looks like a viable alternative to a traditional cylinder head that uses an unusual approach. I wonder if we'll see this enter the mainstream- the one thing I wasn't sure about after reading the article was just how emissions-friendly this engine would be- it incorporates elements from the two-stroke engine, and those aren't the cleanest engines ever.

 

it'd be much easier to read, had the writer realized he's not writing a college thesis full of useless information, and he doesnt need to throw in random banter to fill space.

 

yeah i kinda lost interest or focus at least half way throuh it.

 

So, why is this better than 4-stroke?

I just don't get it...

-MR

 

Fewer moving parts, for one thing. Less loss because there's less to physically move around in the valvetrain. Supports very high revs. I'm not absolutely certain (because yeah, I kinda skimmed the last part of it too), but I think the top piston actually puts out about 9 percent of the power the engine makes, so it's a difference between a loss and a gain.

 

I understand the fewer moving parts thing.

All in all though, how much would all this cost when the classic 4-stroke or even a two-stroke or rotary would work great.

I'm all for new things, but to me this seems like just trying to re-package existing technology.

-MR