anyone how much PSI should be found in each cylinder during a leak down test?

Z4-VILLA · 11-28-2010, 07:30 AM

Just helping a friend so any thoughts would be most welcomed....

krnnerdboy · 11-28-2010, 09:50 AM

Quote:

Originally Posted by Z4-Villalona

Just helping a friend so any thoughts would be most welcomed....

I'm not sure what the psi should be but from my experience they ranged from 175-190, but what's more important is the deviation from each cylinder

Z4-VILLA · 11-28-2010, 05:58 PM

my friend is running 160 across the board after his motor ate itself by way of a timing chain being eaten by the entire valave train....bmw is giving him the standard " go away" attitude. just trying to pick up som info....thanks

JPWEraser · 11-28-2010, 10:57 PM

I presume you mean compression test? If he is doing a leakdown test, there should be less than 10% leakage.

Z4-VILLA · 11-28-2010, 11:05 PM

leakdown

JPWEraser · 11-28-2010, 11:20 PM

A compression test is done by replacing the spark plug in a given cylinder and cranking the engine over without starting it. The maximum pressure recorded from the compression created by cranking the engine is your compression test result. Compression tests are useful for diagnosing faulty piston rings, blown head gaskets, bent valves, or bad valve seals.

A leakdown test is done by placing the cam shafts at top dead center for a given cylinder to effectively "seal" the combustion chamber by closing both intake and exhaust valves and bringing the piston to it's highest stroke point, introducing pressurized air from an air compressor, and recording the percentage of air pressure loss that occurs. If the loss is higher than 10% or so, there are is likely valve damage, piston ring, or head gasket damage. One can also listen to the intake and exhaust tract for rushing air sounds to determine if a leaky valve is on the intake or exhaust valve train of the cylinder that is being tested or if no sound can be heard but air is moving into the crank case, then piston rings are the problem.

Compression tests use less sophisticated tools and can be helpful in initial engine problem diagnosis. Leakdown tests help identify more specific problem areas to track down the actual culprit. Which type of test is your friend doing? I ask this because the results of a leakdown test are not given in PSI but rather a percentage of air pressurization loss.

Also, compression test results will vary depending on the temperature of the engine. A cold engine will produce lower compression numbers than a warm one. As stated above, since there are many variables in the process, the actual number is not the most vital piece of information in the test, but rather the variation between cylinders.

11-28-2010, 07:30 AM	#1
Z4-VILLA Banned 111 Rep 2,460 Posts Drives: Z4M Hardtop Roadster Join Date: Feb 2009 Location: Classified iTrader: (0)	anyone how much PSI should be found in each cylinder during a leak down test? Just helping a friend so any thoughts would be most welcomed....
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11-28-2010, 05:58 PM	#3
Z4-VILLA Banned 111 Rep 2,460 Posts Drives: Z4M Hardtop Roadster Join Date: Feb 2009 Location: Classified iTrader: (0)	my friend is running 160 across the board after his motor ate itself by way of a timing chain being eaten by the entire valave train....bmw is giving him the standard " go away" attitude. just trying to pick up som info....thanks
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11-28-2010, 10:57 PM	#4
JPWEraser Lieutenant 265 Rep 527 Posts Drives: 2016 Corvette Z06/Z07 Join Date: Jul 2010 Location: Union, KY iTrader: (8)	I presume you mean compression test? If he is doing a leakdown test, there should be less than 10% leakage.
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11-28-2010, 11:05 PM	#5
Z4-VILLA Banned 111 Rep 2,460 Posts Drives: Z4M Hardtop Roadster Join Date: Feb 2009 Location: Classified iTrader: (0)	leakdown
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11-28-2010, 11:20 PM	#6
JPWEraser Lieutenant 265 Rep 527 Posts Drives: 2016 Corvette Z06/Z07 Join Date: Jul 2010 Location: Union, KY iTrader: (8)	A compression test is done by replacing the spark plug in a given cylinder and cranking the engine over without starting it. The maximum pressure recorded from the compression created by cranking the engine is your compression test result. Compression tests are useful for diagnosing faulty piston rings, blown head gaskets, bent valves, or bad valve seals. A leakdown test is done by placing the cam shafts at top dead center for a given cylinder to effectively "seal" the combustion chamber by closing both intake and exhaust valves and bringing the piston to it's highest stroke point, introducing pressurized air from an air compressor, and recording the percentage of air pressure loss that occurs. If the loss is higher than 10% or so, there are is likely valve damage, piston ring, or head gasket damage. One can also listen to the intake and exhaust tract for rushing air sounds to determine if a leaky valve is on the intake or exhaust valve train of the cylinder that is being tested or if no sound can be heard but air is moving into the crank case, then piston rings are the problem. Compression tests use less sophisticated tools and can be helpful in initial engine problem diagnosis. Leakdown tests help identify more specific problem areas to track down the actual culprit. Which type of test is your friend doing? I ask this because the results of a leakdown test are not given in PSI but rather a percentage of air pressurization loss. Also, compression test results will vary depending on the temperature of the engine. A cold engine will produce lower compression numbers than a warm one. As stated above, since there are many variables in the process, the actual number is not the most vital piece of information in the test, but rather the variation between cylinders. Last edited by JPWEraser; 11-28-2010 at 11:29 PM..
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