TWO STROKES

Every two stroke motorcycle I have worked on has reed valves at the cylinder intake to prevent exhaust gasses from traveling that direction. They also have at least two schrader valves.

I'm asking that is there any two stroke bike having inlet or exhaust valve instead of ports

The question was asked by myself

It appears that we need more info. Can you sketch a diagram of what you mean?

simply compare the construction with four stroke engine and tell is there any chance to keep the exhaust or inlet valve in 2's engine

The whole point of a two stroke is it's simplicity/reliability... why add valves that you don't need.

The addition of a reed valve on the inlet is sensible as it has very few moving parts and little maintenance.

My old Lambetta had no valves... but it had opened out ports, a primary compression plate, padded flywheel, modified piston skirt, skimmed head, bigger carb' extra clutch plate... and slightly bent forks where my Brother drove it into a wall

Del

I'm confused. I thought Lambetta was a type of soft creamy cheese. So you're saying it goes good with port? Served on a "compression" plate? With a handfull of carbs? Like bread and crackers? And couldn't you have eaten it with your fingers rather than trying to use bent forks?

It's a spelling mistake. Del meant 'Lambretta'.

http://en.wikipedia.org/wiki/Lambretta (other motorcycles are available).

i'm asking only whether there is a possiblity or not ? have u ever tried?

Of course it's possible...I just can't see any point, as your are effectively going to end up with the disadvantages of a two stroke plus the disadvantages of a four stroke.

It's possible to sew two extra legs onto a cat but why would you do it?

TO INCREASE THE VOLUMETRIC EFFICIENCY AND TO REDUCE POLLUTION AND EVEN TO AVOID TWO STROKE ENGINE GOING TO SCRAP

MR.CAT

I can't be bothered to write a dissertation on the two stroke cycle..

If you have a cunning valve arrangement which will 'INCREASE THE VOLUMETRIC EFFICIENCY AND TO REDUCE POLLUTION' lets see it.

I don't see how it is possible, other than the addition of a reed valve on the inlet (which is pretty standard these days) or a rotary inlet valve* (again by no means a new idea) which improves primary compression and allows better operation of the transfer ports.

* The rotary valve can give assymetric inlet opening which of course a piston controlled inlet can't (disscounting the gas momentum effect of course)

I'm sure there are plenty of good books on two stroke tuning...If you were here I could lend you one.

Del

Del

Two stroke motorcycle engines do not have exhaust valves. The main point of the two stroke engines are their simplicity, and the large amount of horsepower they can produce for their size.

When we tune two stroke engines, we usually change the port timing. That is when the exhaust and intake ports open and close with respect to each other. We do this by changing the shape and size of the ports and the shape and vertical size of the piston. Another thing that increases a two stroke engine's power is to "Stuff the Crank." This reducing the open space in the bottom of the engine, which helps increase compression.

Two stroke engines are inherently dirty only because they're designed to lubricate themselves by mixing the oil with the fuel. A very messy solution. This is why most two stroke engines are legal only if they're smaller than a limiting displacement. In most of the US, I think the largest legal two stroke bike engines are no larger than 250 cc.

http://en.wikipedia.org/wiki/2-stroke_power_valve_system

This is not a popet valve, but an adjustment for the shape of the exaust port. A power valve does make a 2-stroke more efficent & pollute less. The amount of lubricant burned is only about 2 times or less than what a GM northstar motor burns by design! Direct fuel injection would improve the emmissions some more. The reason oil is mixed with the fuel is because the crank & back side of the piston are acting as an air pump, described as case reed induction. A traditional crank & piston lubrication scheme could eliminate this need.

There are 2 stroke & 4 stroke diesels.

Two stroke engines are inherently dirty only because they're designed to lubricate themselves by mixing the oil with the fuel. A very messy solution. This is why most two stroke engines are legal only if they're smaller than a limiting displacement. In most of the US, I think the largest legal two stroke bike engines are no larger than 250 cc.

Lies, lies, and more lies!

The inherent dirtiness has very little to do with the oil burned and a great deal to do with the exhaust port timing, which only works, in any practical sense, do to inertia effects (which change with rpm) and sonic effects (which change with rpm).

For good top end power, the exhaust port must be large, and must open when the power stroke is only about half done. Therefore, loads of unburned fuel goes out the port, and a lot of the fresh charge, (coming into the cylinder through the transfer ports) goes out the pipe as well. The whole notion of the transfer ports being open at the same time as the exhaust (and, in fact, there is never a time when the transfer ports are open when the exhaust port is not also open) seems crazy as first glance. In fact, if you take the head off a two stroke engine and turn it through a few revolutions you could come away thinking that the engine should hardly work at all. A good pipe stuffs mixture back into the cylinder just before the exhaust port closes (and after the transfer ports have closed) improving efficiency, but the effect is centered around one rpm (giving highly tuned 2-strokes their famous and fun peakiness).

In a high performance two stroke, the actually exhaust timing is more strongly controlled by acoustic effects in the pipe than by the top edge of the exhaust port. Unfortunately, the speed of sound is fairly constant, but engine rpm is anything but... so this effect only works at a particular RPM. Thus, personal watercraft (Jet Skis, Waver Runners, etc.) used to put about 1/3 of the incoming fuel directly into the water, unburned. The oil is a tiny problem by comparison, with 100:1 ratios being fairly typical at light load in oil injection engines.

With a closed loop injection system and a catalytic converter, a two stroke could be made fairly clean -- and there are direct injection two strokes that will meet current emission standards without suffering a loss in power. However, these are the motorcycles and marine standards, which are less stringent than automotive standards. A 2-stroke could be made to be clean enough for automotive use, but I doubt that it could come close to current 4-stroke power levels, without employing variable port timing, which is difficult to achieve in a 2-stroke.

Way back in early 1970's, (with scarcely any emission controls) concurrent 2-strokes and 4-strokes were comparable in power, with Honda's 4-stroke grand prix bikes often beating Yamaha's 2-strokes. What the 2 strokes gained by having twice the number of power strokes was lost by the ineffectiveness of those strokes, given the early exhaust port opening.

Now, in the US, I think the only legal 2-strokes for road use are 50cc. Because the emission standards are in mass-per-mile, it is tough for anything but the smallest two strokes to meet the standards, with 50cc scooters emitting substantially more than 4000# cars.

Ragavan...

Perhaps if you read this link it will satisfy your obvious thirst for pointless agument.

Del