Reed valve allows the mixture to move in only one direction – from the carburetor to the crankcase. It prevents the mixture from moving back to the carburetor. In the effect reed valve improves reloading of the combustion chamber with fresh air-fuel mixture.
With its air cooled two-stroke engine, it also features a rotating clutch and a chain drive. As the engine increases in power, the clutch plates spin outward, opening up its drive chain.
Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. The physical inertia of reed valves means that they are not as entirely precise in action as rotary valves, a rotary valve engine may run better than a reed valve engine at a small rpm range but the reed valve engine often runs better over a wider rpm range. Once the charge has expanded and mostly left the engine, pressure inside drops again to below-atmospheric values and the reed valve allows fresh air to enter and the cycle be repeated.
Reed valves act as one-way check valves that prevent this backwash. With a lower pressure zone on the engine side, the reed petals flex open to allow fuel/air to pass, when the lower pressure switches to the intake tract side, the reed petals are forced tight against the reed block to seal off the intake tract. With each cycle, the reed petals slap against the reed block, shortening their life span.
how does a chainsaw reed valve work Related Question:
What causes a reed valve to open and close?
As the piston moves upwards in the cylinder a low pressure (vacuum) is created in the crankcase. This vacuum causes the reed valve to open and the air fuel mixture to enter.
What happens when reed valves fail?
Failing reed valves can result in reduced power at what should be cruising speeds. This can be a frustrating symptom as several other factors also can be present with reduced power as the symptom. However, failing reed valves reduces the fuel and air mixture.
How are reed valves opened and closed?
Reed valves are a type of check valve which restrict the flow of fluids to a single direction, opening and closing under changing pressure on each face. Modern versions often consist of flexible metal or composite materials (fiberglass or carbon fiber).
How often should reed valves be replaced?
Reed valve petals wear down over time and should be checked every 15 to 20 engine work hours. If the reed valve petals are chipped, frayed, or no longer create an adequate seal, they should be replaced. There is no standard timeframe to use when changing your reed valve petals.
Do reed valves affect compression?
The intake system, including reeds, does not affect compression readings. Different gauges, engine warm/cold, other plug in/out, rate of turnover while measuring, number of strokes measured all affect readings.
Should reed valves have a gap?
The petals should be seated against the cage with roughly . 015-inch air gap between the frontal edge of the petal and surface of the reed cage. The tolerance for air gap varies slightly by manufacturer, and also varies per each model.
Do all 2 strokes have reed valves?
Not all 2 stroke engines use reed valves, so it is important to know if you even have them. The reed valve is most likely to be present if it just dumps into the crankcase, like the diametrically opposite cylinder.
How many hours do reed valves last?
Always check the instruction manual for your engine before and during assembly. Generally, reed valve petals should be replaced every 100-150 hours.
Will a 2 stroke run without reeds?
No, they won’t run without reeds. As for backfiring through the carburetor, very unlikely unless there was something like a glowing piece of carbon somewhere in the cylinder to light the fuel/air charge before the piston closed the intake port. You should be able to get away with reusing the reed block gasket.
How is valve timing set?
Camshaft. In four-stroke cycle engines and some two-stroke cycle engines, the valve timing is controlled by the camshaft. It can be varied by modifying the camshaft, or it can be varied during engine operation by variable valve timing.
How does a reed block work?
The block fits between the carburetor and the engine. With a lower pressure zone on the engine side, the reed petals flex open to allow fuel/air to pass, when the lower pressure switches to the intake tract side, the reed petals are forced tight against the reed block to seal off the intake tract.
Can you flip reed valves?
Reed valves do not need to be completely closed when at rest. When you flip the prop the vacum in the case will seal it up. As long as your reeds are not frayed and the reed cage has no imperfections then your fine.
Will bad reed valves cause high idle?
Engine difficulties – damaged reed valve petals can leave less air in the cylinder, increasing the difficulty of starting the engine, as the cylinder would lack energy. There is similar difficulty to having a difficult start to rough idling; in this case, the engine may not start quickly enough.
How long should reeds last?
A good rule of thumb is you should replace your reed every 2-4 weeks, no matter how often you’re playing your instrument. You may want to replace your reeds more frequently if you’re practicing several hours each day. Some reeds also may not last as long as others, every reed plays slightly differently.
Can you flip reeds?
Yes, you can flip reeds. If that doesn’t fix the reeds not sealing, get new reeds. As for your compression, pull the head and check the bores.