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Cylinder compression leak-down test. Procedure?
Thank you in advance.
Joe
Thank you in advance.
Joe
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Re: Just For The Halibut
once you have the gauge you need to keep the piston at TDC before putting in the air pressure or the engine will spin over and you will not get a reading. with the engine in the car get the cly you are checking to TDC and have someone put the trans in gear and hold the brake. on a engine stand you need a flywheel lock. if you are lucky you can get the piston at exactly TDC and it will stay there when you apply the air pressure but that is a crap shoot. they sell a "whistle" that you put into the spark plug hole and as you come up on compression you hear the whistle and when it stops you have reached TDC -
Re: Just For The Halibut
Clem:
I haven't been able to find anything on leak down testing. How much pressure must I apply to the cylinder? Is it supposed to hold pressure for a certain length of time? Is there a special gauge(s) needed? Must I maintain a flow of air into the test cylinder? The only specific info that I have found (on the web), is that I must listen for air escaping thru the carb, exhaust, or crankcase--how much release is considered normal?
Thanks in advance.
JoeComment
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Re: Just For The Halibut
you need a "leak down tester" and cost about $70. they take 80/100# of air pressure and you read the leakage directly off of the gauge in percent. if you have a high percentage of leakdown,25% or more the engine has a problem. air coming up thru the carb could mean leaking intake valve,out the exhaust could mean a leaking exhaust valve or could mean some carbon under the vale seat and you can test this by hitting that valve tip with a deadblow hammer to loosen up any carbon by letting the valve slam shut. if the rings are leaking you will hear air rushing into the oil pan.Comment
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Thanks Clem *NM*
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Re: Thanks Clem
goto google and type in "leakdown tester" and you will find all kinds of info even how to build your own and where to buy.Comment
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Re: Thanks Clem
Clem and Joe-----
I tried building my own once-upon-a-time and I found that purchasing all the pieces was just about the same cost as purchasing a moderately priced set-up. Plus, the one I made never worked very well (much to my disappointment and chagrin).
I recommend only the "dual gauge" type units. Tavia makes one of these that works very well and sells for about $75 from sources like Summit Racing. It comes with complete instructions, too.In Appreciation of John HinckleyComment
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Re: Thanks Clem
You can buy the Tavia online here for $69...I think the key to a good unit is the orifice restriction that gives the reading between the two guages since this is an air flow comparator. This link is from the famous Google search!...Craig
Tavia Leak Down TesterComment
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Thx Joe
Joe - I have all the parts laying around, but never got around to assembling. Based on your input and experience, I just ordered the Tavia from the website I posted. Last thing I need is false indications....thx!....CraigComment
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Re: Just For The Halibut
If your taking a compression test to determine PSI. I check each cylinder first, then add a quirt of oil into the cylinder and check again. If PSI is the same (high)Carbon. If the PSI is the same (low) valve leak. If the PSI goes up rings leaking.I'm just cheep and so is a little oil.Comment
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Compression Update:Thanks All
Pulled all the plugs and did a conventional compression test on a cold engine (4 cranks/cyl, WOT, no oil squirt was needed). All cylinders registered 195 psi, plus or minus 5psi, which is slightly higher than it was when I first assembled the engine (the rings took a good set). To my mind, this made a further leak down test unnecessary, but I have learned much from those who contributed to this thread, and I thank you all.
The reason for this exercise was a wet #2 plug after a road test where the engine broke up @ 5500 RPM. Valve seals on the #2 cyl are intact, and compression showed 197psi. I cleaned and reinstalled #2 plug, and took another road test, this time with shift points at a more sedate 4000 rpm- the engine ran normally, with no breakup. Returned home to find #2 plug DRY. This leads me to agree with Duke, that points bounce is the likely suspect, and that this caused #2 to misfire, fouling the plug. The thing I am not sure of, is that the liquid on the plug was viscous, like oil. Could it be that the unburned gas became thick (much the same as a reduction in cooking) when the lighter components flashed off but did not ignite during the period of misfire.
JoeComment
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