Leak down testing
02-06-2003, 02:21 PM
#1
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Leak down testing
Taking this topic from another listing regarding piston ring gap clearance.
What is the general procedure for performing a leakdown test... considerations,steps..etc.
Is it outlined in the workshop manuals??
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
What is the general procedure for performing a leakdown test... considerations,steps..etc.
Is it outlined in the workshop manuals??
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
02-06-2003, 10:32 PM
#2
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Tony,
A leak down test will pin point a host of problems. You are going to need a leak down gauge, and air compressor. Bring the piston being tested to TDC on the compression stroke this will ensures the valves are closed Install the gauge , pump air into the cylinder, the gauge instructions will tell how much air to pump. A 0 (zero) reading is a perfect cylinder ;( zero leak down) but we know nothing is perfect. Less than 10% is good, 20% is fair and 30% is poor. If the test indicates a leak of more than 20%, then listen for air leaking at different locations. crankcase leakage , PVC, oil dip stick = worn or broken rings worn or broken pistons. Air from the throttle body or air cleaner = leaking intake valves, air from the exhaust = leaking exhaust valves, bubbles from the radiator holding tank = head gasket, cracked head or block
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
A leak down test will pin point a host of problems. You are going to need a leak down gauge, and air compressor. Bring the piston being tested to TDC on the compression stroke this will ensures the valves are closed Install the gauge , pump air into the cylinder, the gauge instructions will tell how much air to pump. A 0 (zero) reading is a perfect cylinder ;( zero leak down) but we know nothing is perfect. Less than 10% is good, 20% is fair and 30% is poor. If the test indicates a leak of more than 20%, then listen for air leaking at different locations. crankcase leakage , PVC, oil dip stick = worn or broken rings worn or broken pistons. Air from the throttle body or air cleaner = leaking intake valves, air from the exhaust = leaking exhaust valves, bubbles from the radiator holding tank = head gasket, cracked head or block
<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
02-07-2003, 10:17 AM
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Tony,
A little theory on the gauge: Actually there are two gauges, one on each side of a fixed orifice, (~.040", ~1" long. Compressed air is fed into the first gauge and then through the oriface to the second gauge and then into the cylinder. The leakage of the cylinder makes the second gauge read less pressure. The difference is the leakdown rate. FYI, My '88 (now Jim Morehouse's) had a leakdown of ~2%, at 90K miles which is considered excellent for a racing engine.
A little theory on the gauge: Actually there are two gauges, one on each side of a fixed orifice, (~.040", ~1" long. Compressed air is fed into the first gauge and then through the oriface to the second gauge and then into the cylinder. The leakage of the cylinder makes the second gauge read less pressure. The difference is the leakdown rate. FYI, My '88 (now Jim Morehouse's) had a leakdown of ~2%, at 90K miles which is considered excellent for a racing engine.
02-07-2003, 10:42 PM
#4
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1-3% you will retain 99% power
4-8 you are down around 5% power
over 10%, your engine is lucky to make 80% rated power
Just my experience with leakdowns and dyno pulls!
Marc
devek
4-8 you are down around 5% power
over 10%, your engine is lucky to make 80% rated power
Just my experience with leakdowns and dyno pulls!
Marc
devek