low compression
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Joined: May 2008
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From: Mount Holly, NC
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Cruiser
Joined: Jun 2009
Posts: 172
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Low Compression
Be sure to run the compression test more than once to confirm the results.
If you get the same thing, then try adding a tablespoon of motor oil to the cylinder and test it again. If the compression goes way up, like doubles, then the problem is the rings or cylinder. If the compression doesn't change, then the problem can be a valve or leaking head gasket or a cracked head. (If it were a hole in the piston, you'd have a great deal of smoke.)
The easiest way to locate the compression leak is to use low pressure air in the cylinder with the piston at TDC on the compression stroke. By low pressure, I mean 30-40 psi. If it is a leaking intake valve, you'll hear the leak at the carburetor. If it is a leaking exhaust valve, you'll hear it at the exhaust pipe. If it is a leaking cylinder head gasket, you'll hear it at the joint between the head and the cylinder.
Good luck.
If you get the same thing, then try adding a tablespoon of motor oil to the cylinder and test it again. If the compression goes way up, like doubles, then the problem is the rings or cylinder. If the compression doesn't change, then the problem can be a valve or leaking head gasket or a cracked head. (If it were a hole in the piston, you'd have a great deal of smoke.)
The easiest way to locate the compression leak is to use low pressure air in the cylinder with the piston at TDC on the compression stroke. By low pressure, I mean 30-40 psi. If it is a leaking intake valve, you'll hear the leak at the carburetor. If it is a leaking exhaust valve, you'll hear it at the exhaust pipe. If it is a leaking cylinder head gasket, you'll hear it at the joint between the head and the cylinder.
Good luck.
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Road Master
Joined: Jun 2006
Posts: 933
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If it bleeds off the compression gauge is leaking.They have a valve in the end of the hose to keep the pressure in.The valve needs to be removed to air check a cylinder by the way.
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