You find two-stroke engines in such devices as chain saws and jet skis because two-stroke engines have three important advantages over four-stroke engines:. These advantages make two-stroke engines lighter, simpler and less expensive to manufacture.
Two-stroke engines also have the potential to pack about twice the power into the same space because there are twice as many power strokes per revolution. The combination of light weight and twice the power gives two-stroke engines a great power-to-weight ratio compared to many four-stroke engine designs.
You don't normally see two-stroke engines in cars, however. That's because two-stroke engines have a couple of significant disadvantages that will make more sense once we look at how it operates. How Maglev Trains Work.
Prev NEXT. Two-stroke Basics. Two-stroke engines do not have valves, which simplifies their construction and lowers their weight. Two-stroke engines fire once every revolution, while four-stroke engines fire once every other revolution. This gives two-stroke engines a significant power boost.
Two-stroke engines can work in any orientation, which can be important in something like a chainsaw. A standard four-stroke engine may have problems with oil flow unless it is upright, and solving this problem can add complexity to the engine.One of the better improvements incorporated into the 2-stroke engine occurred during the s when power valves were introduced allowing a broader power band instead of all the power on the low end or all the power on the top end.
Power valves, also known as exhaust valves, open and close the exhaust port allowing the engine to produce steady power based on the roll of the throttle. So, whether a rider opens wide at the start or on a straight-away power valves ensure top performance at either end without taking you for an unnecessary thrill ride.
Some of those older models offered two options: no power or maximum power and nothing in between. Several scenarios result in clogged or sticky valves giving you a slight idea of what it was like to race in the 70s with a diminished power band but mostly just frustrate the heck out of you.
A sticky valve takes longer to open or close making the bike hard to ride. Clogged power valves love to eat spark plugs and you won't get much top end. If you're burning through plugs or having trouble opening wide once up to speed it's a good idea to check the valves.
It's an easy fix at least in terms of cleaning the actual valves. Unfortunately, you'll also perform a top end rebuild so you'll need a kit. Reaching the valves on most bike models depends upon removing the cylinder which means breaking the gasket seal. Don't reuse the gasket! Besides, dirty power valves usually mean a top end rebuild is in your near to immediate future anyway. Note: Some power valve designs allow for cleaning without removing the cylinder but most 2-strokes require it.
The cylinder houses the power valves which look a bit like airplane flaps see diagram. You'll need to remove the bolts to extract the valves. But check your service manual before removal. Once removed, scrape off any carbon build-up using steel wool or a stiff toothbrush then apply contact cleaner or other similar solvent brake cleaner, gasoline to finish the job.
You can leave them soaking in the cleaner while you prepare for the top end job. Reinstall the valves to spec and continue with the regular top end job. You can adjust most power valves for lower or high-end speed but not all manufacturers use the same method.
KTM uses a tensioner and spring contraption while Honda uses a cable operated system. Adjusting the valve enables you to increase power on the bottom or top end depending on your preference. Eventually, all power valves gum up when not serviced regardless of the quality of gas and oil. However, regular tune-ups and using the correct premix goes a long way towards keeping the exhaust port open, the valves working properly and you riding.
Dirt Bike. By: AndrewT November 03, Tags: Dirt Bikes dirt bike tech tips Andrew Tuttle how to.Reed valves on a two-stroke engine tend to be somewhat temperamental, as the inner workings of the assembly are very sensitive. However, reed valves are often worth the time it takes to troubleshoot, since the design cuts off backflow and makes carburetion more efficient in a two-stroke engine. Solving many of the problems with reed valves includes eliminating other issues that could cause failures.Cleaning YZ250 Stuck Powervalve
Turn on the motorcycle or scooter engine and get it running, if possible. Wait about five minutes for the engine to warm up. Pull on the throttle to see if the carburetor responds correctly and quickly. Turn the engine off. Turn the fuel supply off. Use a screwdriver to disconnect the banjo clamp holding the carburetor to the intake hose connecting to the reed valve manifold on the engine.
Pull the carburetor free and disconnect the fuel line connected to the side of it. Use a crescent wrench to disconnect the fuel line.
Hold the end of the fuel line in your hand with a shop rag and slowly turn the fuel supply on to see if fuel is flowing properly.
Turn it off when fuel begins to spill out onto the rag.
Place the carburetor and fuel line aside. Unscrew the banjo bolt holding the intake hose to the reed valve manifold. Put the hose and clamps aside. Look inside the reed valve manifold to spot any signs of damage to the internal reed petals. Use a socket wrench and sockets to remove the manifold from the engine intake. Pull the reed valve manifold apart by hand once it is loose from the engine. Take out the old reed petals and replace them with a new set. Re-bolt the reassembled manifold to the engine again with the socket wrench.
Screw on the intake hose clamp after reinstalling the hose. Reconnect the fuel line to the carburetor and reinstall the carburetor to the intake hose. Tighten the securing clamp on the hose locking the carburetor in place.
Turn the fuel flow on again. Turn the engine on again and try out the response. Take the motorcycle or scooter for a ride to test performance. This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.
To submit your questions or ideas, or to simply learn more about It Still Runs, contact us. Step 1 Turn on the motorcycle or scooter engine and get it running, if possible. Step 2 Use a screwdriver to disconnect the banjo clamp holding the carburetor to the intake hose connecting to the reed valve manifold on the engine. Step 3 Hold the end of the fuel line in your hand with a shop rag and slowly turn the fuel supply on to see if fuel is flowing properly.
Step 4 Place the carburetor and fuel line aside.The two-stroke power valve system is an improvement to a conventional two-stroke engine that gives a high power output over a wider RPM range. A stroke is the action of a piston travelling the full length of its cylinder.
In a two-stroke engine, one of the two strokes combines the intake stroke and the compression strokewhile the other stroke combines the combustion stroke and the exhaust stroke.
As the piston travels upward in the cylinder, it creates low pressure area in the crankcase ; this draws fresh air and atomized fuel from the carburetor through a hole in the cylinder wall or directly into the crankcase. As the piston continues travelling upward, transfer ports and the exhaust ports are closed off, thus trapping the combustible mixture in the combustion chamber. As the piston reaches the top of the cylinder, the mixture in the cylinder is compressed to the point of ignition.
The second stroke begins once ignition has taken place. The power stroke begins after the air-fuel mixture is ignited.
The burnt fuel creates pressure in the cylinder above the piston and forces it downward. As the piston passes the midpoint of the downstroke, the exhaust port to the side of the cylinder is uncovered and initiates the flow of burned fuel out into the expansion chamber or muffler through the manifold. The piston then moves downward, where the air-fuel mixture remains from the previous intake-compression stroke. Shortly after the exhaust port is uncovered by the downward travel of the piston, the transfer ports begin to be uncovered.
The transfer ports act as a passage through which the air-fuel mixture moves from the crankcase into the cylinder above the piston. Once the piston reaches the bottom of the stroke, the second stroke is completed and the process is repeated.
Beta 2-stroke Power Valve Spring Kit
The only moving parts inside simple two-stroke engines are the crankshaft, the connecting rod, and the piston. It is the same simplicity in design, however, that causes a two-stroke engine to be less fuel-efficient and produce high specific levels of undesirable exhaust gas emissions. At the bottom of the power stroke, the transfer ports, which deliver fresh fuel-air mixture, are open at the same time as the exhaust port. This can allow a significant amount of fresh fuel to run straight through the engine without being burned in the process of power production.
Properly designed exhaust systems help minimize the amount of raw fuel loss in the exhaust process, but a carbureted two-stroke engine will always waste some fuel modern direct injected engines avoid this. Many producers of two-stroke performance bikes fit them with the exhaust power valve systems. These valves act to vary the height and width of the exhaust port thereby broadening power delivery over a wider rev range.
Exhaust ports with fixed dimensions only produce usable power in a narrow rev range, which also affects fuel consumption and emissions. In a race bike, this is not a problem as the engine will be operating at high RPM almost all the time. To provide more low RPM power, as well as enable the engine to produce a lot of high RPM power, a power valve system is used. All power valve systems vary the duration of the exhaust port open time, which gives the engine usable low end power combined with excellent top end power.
Manufacturers have also included sub exhaust chambers that extend the 'tuned length' of the expansion chamber. Power valve actuation can be by mechanical RPM dependent or electric servo motor means increasingly with electronic control. Electronic control offers a greater degree of accuracy as well as being able to vary the opening of the valve and be tuned to conditions.
With the AETC system, the power-valve systems are normally partially closed at low RPM; when closed, it enables the engine to make more power.
Changing the power of 2-stroke engine
Up to a certain point, however, power drops off as the engine is unable to expel enough gases out of the exhaust. When the power-valve is opened, it allows more gases to flow out of the exhaust port.
This system is recognizable by a small box above the exhaust outlet; the power-valves are situated in this box. Depending on the valve, they may be made of two older version or three newer version separate blades.
YPVS Yamaha engines, Yamaha Power Valve System: Yamaha engineers realized that by altering the height of the exhaust port they could effectively change the engine power delivery thereby having optimal power and torque across the entire rev range, so it was that the YPVS was born.COM Enter keywords or a search phrase below: Search.
What Tires Should You Use? American Snowmobiler Gear. American Snowmobiler Back Issues. American Snowmobiler Calendar. Login or Register Customer Service. By Olav Aaen November 7, Our 2-stroke sleds are incredibly high-tech compared with just a few years ago. History and operation The name powervalve comes from its original use in racing, and it first appeared on Yamaha moto-cross bikes. Motocross engines need to have long and torquey power bands to be consistently fast on twisty circuits mixed in with short fast straights that require maximum power for quick acceleration.
As power increased at higher rpm levels, so did the height of the exhaust port. With taller ports and the use of more powerful expansion chamber exhaust systems, bottom end torque suffered. Fortunately, this downfall was improved somewhat by the use of reed valve inlets instead of the long popular and simple piston port intake.
This tuning frequency is in part determined by the exhaust port opening time. If the exhaust opening time could be varied with the engine speed, a steadier power curve with more torque at lower engine speed could be achieved transitioning smoothly into the higher top end power as the engine speed increased.
This could be done without suffering the sudden burst of power that made machines sometimes difficult to control when the pipe came on. Yamaha was the first manufacturer to offer powervalves on their motocross racing bikes, and other competitors quickly followed with their own design. The 3-D mapping determines their operation. Team blue filed for patents on their system as early as Their power valve was a pure racing application until when Yamaha introduced their liquid-cooled twin road bike with the designation YPVS Yamaha Power Valve System.
In the first powervalves appeared on a snowmobile race sled.Changing the power of 2-stroke engine is really very simple when you know the basic techniques of 2-stroke engines.
Most of the errors is to choose a less appropriate combination of engine components so that the engine actually ran worse than standartever experienced? Since modifying the 2-stroke engines require not only a big budget in funding but also modification strategies.
But the simple craftsmanship, careful, and postpone for later extreme modification could be the key performance 2-stroke engine. Although invisible to the machine 2 is more simple than 4 stroke engines, with very few components, only the piston within the cylinder, but actually not very complex machine 2 in the calculation: The main use of motion dynamics in a gas engine to generate power.
There are different phases that are very influential in the crankcase and cylinder block in at the same time, so the second machine was unable to work more efficiently just enough degree crankshaft rotation, compared with degrees of crankshaft rotation by engine 4 stroke is what caused the explosion 2-stroke engine power than the 4 stroke stung.
Secret 2-stroke engine power is the primary and secondary compression settings in the machine. This is why we often suggest the rat rider if you want to send the machine to work on all engines or motors should be packaged and gentlemen, because not enough just to modify the block or head only. Let us examine how 2-stroke engines work in the gas dynamics:. The driving force of the piston is pressed into the crankcase gases to cause the petals open. Compression on a crutch is important to create a suction force on the reed valve, moreover assisted membrane such as V-Force reed valve with a lot of compression so that even low fresh gas mixture is able to easily enter.
At 90 degrees crankshaft angle, and the piston is in the maximum negative acceleration, exhaust ported open as a sign of the end of the business step. The hot gas will be wasted by itself out to the exhaust. Compression on a crutch began to weaken during the transfer port begins to open. The pressure in the cylinder must be reduced lower than the pressure in the crankcase with the aim that unburned gas can out of the transfer ports during the flushing.
Flushing begins. That is fresh out of the ported gas transfer and fused to form a cycle. The gas will move upward toward the rear cylinder and spins continue rinsing residual combustion gases from the power stroke.
It is important that the rest of the combustion gases must be removed completely, to open up room for the mixture of fresh air into the combustion chamber. That is the key to making big power on a two-stroke engine.
Now the fresh gas also wasted until the headers on the exhaust. But this fresh gas will not get away with it because it has a compression pressure wave reflection from the end of the exhaust pipe design is good, to bring the package back into the fresh gas cylinder before the piston closes the port hole.
This shows how important it is 2 stroke exhaust design, calculations done to reduce the trial n error is needed. Being able to see the difference? Can make a picture of how to design a 4 stroke engine to be able to fight the 2-stroke motorcycle engine? Compression waves which bounce off the exhaust pipe carrying fresh gas back through the exhaust port now also serve as the inlet port is not it? As the piston closes the port then the compression begins.
In the crutch, the pressure becomes lower than atmospheric pressure, causing a vacuum and this will open the suction valve reed and put fresh gas into the crankcase. And the cycle will continue over and over. Learn how to process basic 2-stroke engine works. When porting begin to open and closed in crankshaft degrees duration, we will undoubtedly be modifications on the right path.
Porting the cylinder designed by engineers to create energy in a certain RPM range resulting in engine character of its own. For example, riding a RM on rocky mountain setting that staff need more shows on lap down — because the middle of the valley and climb the mountain air humidity. How are we able to modify a machine? Previously we have to get as much data and information about the characteristics of standard machine manufacturer.
Ported area size and duration associated with engine capacity and RPM similar duration Noken not? Ease of us understand the 4 stroke engine will take us to a deeper understanding of the dynamics of 2-stroke engines.The power valve is a movable flap located on the cylinder exhaust port of a two-stroke engine — where burnt gasses are flushed out of the cylinder.
At low RPM, the flap is held partially closed to make the exhaust port smaller. This helps the engine generate torque at low speeds. As revs build, the flap gradually opens, expanding the size of the exhaust outlet for greater top-end power. The ability to vary the size of the exhaust port gives your two-stroke engine broad, usable power. The power delivery characteristics of the engine are affected by the timing and speed at which the power valve opens. The ideal power delivery isn't necessarily the same for all riders or riding conditions, so many riders find it beneficial to alter power delivery characteristics to suit the available traction and their personal preferences.
This adjustment determines when the exhaust flap starts to open. This is what the PowerDial helps you adjust. Your KTM came with green, yellow, and red auxiliary springs. Dynamometer runs depicting the effect of power valve preload settings. Test conducted with yellow auxially spring. Power Valve Tuning. What is a power valve? Why adjust it?
How do I adjust it?