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Posts Tagged ‘Compression’

Small Engine Repair: Husqvarna Chainsaw Compression Test With Decompression Valve Open & Closed

Written by Tools on Monday, November 7th, 2011 in Power Equipment.
Tags: Chainsaw, Closed, Compression, Decompression, Engine, Husqvarna, open, Repair, Small, Test, Valve

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**Always follow the instructions in your repair manual when doing repair or maintenance work on Outdoor Power Equipment. Manuals can be found at the manufacturers website.** In this video I show the effects a decompression valve has on the engine’s compression. The decompression valve controls whether or not a channel inside the cylinder is open or closed. The channel runs from inside the cylinder to outside the engine. When the valve is open it allows a small amount of air inside the cylinder to escape, making the engine it easier to turn the engine over and start. Once the engine starts, the high pressure created by the ignition of the air and fuel mixture closes the decompression valve and the engines compression returns to normal.

Small Engine Repair: Homelite Chainsaw Compression Test Piston Rings Cylinder Damage

Written by Tools on Tuesday, November 1st, 2011 in Power Equipment.
Tags: Chainsaw, Compression, Cylinder, Damage, Engine, homelite, Piston, Repair, Rings, Small, Test

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**Always follow the instructions in your repair manual when doing repair or maintenance work on Outdoor Power Equipment. Manuals can be found at the manufacturers website.** The Homelite Chainsaw in this video is over 30 years old. It had a carburetor problem, which caused the air fuel mixture at top speed to be lean, and this caused the chainsaw to over heat and lock up. I was able to free the piston by spraying penetrating oil into the cylinder, and now the chainsaw runs again. However, the piston, rings and cylinder have signs of damage caused from the engine over heating, but the compression ratio is still very high. The compression ratio is close to 150 psi. If you knew nothing about this saw, and performed a compression check, most mechanics would assume the top end is in good working order. This goes to show that you can’t always assume the top end is ok when the compression ratio is high. It requires a visual inspection. On small 2 stroke engines used on outdoor power equipment an easy way to see damage on the piston and rings is to remove the muffler and look at the piston and rings through the exhaust port.