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Compression Testing

 

A compression tester is a useful diagnostic tool, and readily available from Sears or auto parts stores. Buy the threaded type and make sure the kit comes with an adapter that matches the spark plug threads of your engine. Performing a compression test is simple. Start by removing the spark plug, thread in the adapter, and hold the throttle wide open and the kill button on. This will prevent any spark and enable the engine to draw in maximum airflow. Then kick-start the engine several times until the needle on the pressure gauge peaks. The pressure reading depends on two main factors; the compression ratio and the altitude at which the engine is being tested. The compression ratio will also depend on if the engine is equipped with exhaust valves and their condition. When the exhaust valves are in the closed position the compression ratio will be greater than if the valves are carbon-seized in the open position. The difference may yield a pressure reading 25 psi. The quality of compression testers varies greatly. The main thing that a compression tester can identify is a change in condition. Whenever you rebuild the top end, take a compression pressure reading and mark it down. When the pressure changes 20% check the condition of the piston and rings. Pistons usually last twice as long as rings.

 

P.S: Buy the tool for removing the sparkplug.

 

If something isn't clear, tell.

 

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155

A fresh stock banshee motor should be more like 125, not 155. Anything under 100 PSI, or more than a 10% difference in pressure between the two cylinders means you are ready for a rebuild (on a stock motor). Also, two strokes do not have exhaust valves. I don't think thats what he was saying, but just to clear up any confusion for a new 2stroke owner...

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  • 2 weeks later...

Alrighty.. so i leave the other spark plug in correct? And then i put the other plug back in and test the other cylinder?

 

Doesn't matter, you can leave one plug in and test the other side. Your going to do both jugs anyway, might as well take them both out for comp test, they are separate cyl's. Just makes it a little easier to kick over with them both out.

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