Urban Myth
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Senior User
Joined: Feb 2005
Posts: 214
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From: Kalgoorlie Australia
Urban Myth
G'day guys, I read(or heard, can't remember) years ago that you could diagnose a cylinder with no compression as rinds/pistons or valves by putting a piece of paper over the exhaust. The story went that if the paper sucked back against the end of the pipe for a split second every cycle that the problem was a valve, just wanting to know what you guys think/know. I have a 351C with a dead cylinder that I have to fix so I tried the paper trick first and it sucks in, want to know if it is an engine out fix or just a heads off.
More Turbo
Joined: Nov 2003
Posts: 682
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From: Peoria, IL (more or less)
One method, if you've got access to a compression tester, is to get a baseline reading; then shoot some heavy oil into the cylinder, spin the crank a few times, & retest. If the reading now goes way up, it's the rings. If not, it's the valve(s).
Doesn't hurt to repeat this a few times to make sure you are fully coating the cylinder walls with oil. Good luck-
Doesn't hurt to repeat this a few times to make sure you are fully coating the cylinder walls with oil. Good luck-
Thread Starter
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Senior User
Joined: Feb 2005
Posts: 214
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From: Kalgoorlie Australia
To me it doesn't sound "poppy" enough to be a burnt exhaust valve but also it isn't making any engine noise so I doubt it is a lifter or holed piston, I would just like to find out before I go and pull the engine.
Mountain Pass
Joined: Dec 2005
Posts: 133
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From: Mackinaw City, MI
If you introduce compressed air into the cylinder, it should hold or it could give you 3 possible symptoms: air coming out tailpipe(burned EXH valve), air coming up thru carb(burned INT valve), or air trying to escape thru dipstick tube or oil filler cap/pcv valve( excessive blowby, cracked or stuck rings). None of the last 3 things are a good thing.
