Compression Test, Leakdown Test. Someone explain it to me?
Compression Test, Leakdown Test. Someone explain it to me? I really dont know much about this. Would someone please explain to me how it is done, what to look for? An overall explaination. What tools are needed. Links to this info, anything!
Thanks.
Thanks.
Compression test:
Compression guage needed. Line from comp. guage to any given cylinder via spark plug hole. *DISABLE THE FUEL PUMP/INJECTOR/IGNITION SYSTEMS, by pulling those fuses before cranking over the motor. Remove the spark plugs. Block the throttle to WOT position. Crank over engine at least 7 compression strokes, and watch the guage. Low comp. on the first stroke, followed by graduall increasing pressure on successive strokes indicates worn rings. Low comp. on the 1st stroke, which doesn't build up during successive strokes indicates leakin valves or a blown head gasket. Record the highest guage reading obtained for that cylinder.
Repeat this procedure for all other cylinders.
Cylinder compression pressure should not be below 100 psi on a stock piston/head setup. Max. variation should not be more than 30% between cylinders.
If readings are are below normal, add about 3 squirts of oil to the cylider and repeat procedure. If comp. rises after oil is added to cylinder, rings are bad. If the comp. doesn't go up, the prob. is at the valves or head gasket.
If 2 adjacent cylinders are showing an equally low reading, odds are it's a blown head gasket. If you see the compression is way down or varies greatly between cylinders....do the leak down.
Leak down test:
This test will show condition of upper end components (ie): guides, seals, seats(bent valves), rings, or head gasket, and pinpoint where the problem lies. Motor "should" be as close to operating temps. as possible.
Leak down guage/compressed air needed. Line from compressor to guage, line from guage to any given cylinder via spark plug hole. With piston at TDC(compression stroke), apply air (I usually do 100 psi). Guage will show % of leak down for that cylinder.
Compression guage needed. Line from comp. guage to any given cylinder via spark plug hole. *DISABLE THE FUEL PUMP/INJECTOR/IGNITION SYSTEMS, by pulling those fuses before cranking over the motor. Remove the spark plugs. Block the throttle to WOT position. Crank over engine at least 7 compression strokes, and watch the guage. Low comp. on the first stroke, followed by graduall increasing pressure on successive strokes indicates worn rings. Low comp. on the 1st stroke, which doesn't build up during successive strokes indicates leakin valves or a blown head gasket. Record the highest guage reading obtained for that cylinder.
Repeat this procedure for all other cylinders.
Cylinder compression pressure should not be below 100 psi on a stock piston/head setup. Max. variation should not be more than 30% between cylinders.
If readings are are below normal, add about 3 squirts of oil to the cylider and repeat procedure. If comp. rises after oil is added to cylinder, rings are bad. If the comp. doesn't go up, the prob. is at the valves or head gasket.
If 2 adjacent cylinders are showing an equally low reading, odds are it's a blown head gasket. If you see the compression is way down or varies greatly between cylinders....do the leak down.
Leak down test:
This test will show condition of upper end components (ie): guides, seals, seats(bent valves), rings, or head gasket, and pinpoint where the problem lies. Motor "should" be as close to operating temps. as possible.
Leak down guage/compressed air needed. Line from compressor to guage, line from guage to any given cylinder via spark plug hole. With piston at TDC(compression stroke), apply air (I usually do 100 psi). Guage will show % of leak down for that cylinder.
TECH Veteran
Joined: Aug 2002
Posts: 4,055
Likes: 1
From: Hartsdale, NY
...i just bought a compression guage set ($79) and leak down guage ($69) from JC Wittney...
..they have some decent tools for cheap... www.jcw.com
...unfortunately, they are not a sponsor, however..
..they have some decent tools for cheap... www.jcw.com
...unfortunately, they are not a sponsor, however..
"All Motor 9 Second club member"
iTrader: (60)
Joined: Nov 2001
Posts: 3,235
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From: On the Bumper!
BLKWS6- I just did a compression test on my H/C set up and got on average 225 psi. The highest was 228 and lowest was 215. the rest stayed close to 225 psi. I know several cars with non-shaved heads and fly cut pistons that are around 165-190 psi. I hope that helps out. Keep us posted on the results.
James
James
