Leak Down Test?
Thread Starter
On The Tree
Joined: Nov 2001
Posts: 120
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From: Washington, D.C.
Leak Down Test? About to do a "leak down" test on my 98 SS>
346 stock bottom end.
Never done this before, but as I understand it, you pump air into the cylinder thru spark plug port and monitor how long it takes the air to leak out....this is supposed to indicate any problems with the rings. Has anyone done this before? What kind of numbers should I be looking for?
Thanks for your help!
Chuck
346 stock bottom end.
Never done this before, but as I understand it, you pump air into the cylinder thru spark plug port and monitor how long it takes the air to leak out....this is supposed to indicate any problems with the rings. Has anyone done this before? What kind of numbers should I be looking for?
Thanks for your help!
Chuck
Re: Leak Down Test? Another tip from Cartek's webpage...
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">It is extremely helpful to use a leak down tool in finding out if your motor is in poor condition. A helpful hint -- if a cylinder is showing high leak down numbers and you want to know what is leaking in the cylinder, blow smoke into the cylinder through the tool air hose, then connect the shop air into it and look for the smoke. If the smoke comes out of the tail pipe, then the exhaust valve may be bad. If smoke comes out of the throttle body (blades open) then the intake valve may be bad. If the smoke comes out of the breathers or dipstick tube, it's going past the rings. If it comes out of the radiator cap opening or an adjacent cylinder's spark plug hole, then the head gasket may be bad.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">It is extremely helpful to use a leak down tool in finding out if your motor is in poor condition. A helpful hint -- if a cylinder is showing high leak down numbers and you want to know what is leaking in the cylinder, blow smoke into the cylinder through the tool air hose, then connect the shop air into it and look for the smoke. If the smoke comes out of the tail pipe, then the exhaust valve may be bad. If smoke comes out of the throttle body (blades open) then the intake valve may be bad. If the smoke comes out of the breathers or dipstick tube, it's going past the rings. If it comes out of the radiator cap opening or an adjacent cylinder's spark plug hole, then the head gasket may be bad.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
Thread Starter
On The Tree
Joined: Nov 2001
Posts: 120
Likes: 0
From: Washington, D.C.
Re: Leak Down Test? WOW! Thanks for the responses. Went thru the painful process of the leak down test today ( the hard part is making sure the cylinder is at TDC)... everything was within acceptable %'s. Learned alot of tricks from your replies that I wish I had known before starting the process. Oh well, will only be easier the next time. This testing started because someone thought that they saw smoke after a 150 shot nitrous run...the car is running really rich on the nitrous runs, so maybe that was what they saw. nevertheless..I'm too close to the 9's on a stock bottom end to give up now, so I'm gonna go for it! Wish me luck. either a first or Kaboom!
Chuck
Chuck
Re: Leak Down Test? Chuck,
Its really very easy. You need a regulated source of air. I like to set the regulator to 100psi since this makes the %leak calculation easier.
First, get the cylinder you are going to check to TDC on the compression stroke (both valves closed.) Second, thread the tester into the spark plug hole for that cylinder and connect the regulated 100psi air source. Third, read the gauge on the tester.
If you are using 100psi and the tester reads 100psi, then you have 0% leakdown. 90psi would mean 10% leakdown, etc. Basically the equation is 100%-leakdown pressure/incoming pressure.
I would look for numbers in the range of 8%-10% as good.
Hope this helps.
Shane
Its really very easy. You need a regulated source of air. I like to set the regulator to 100psi since this makes the %leak calculation easier.
First, get the cylinder you are going to check to TDC on the compression stroke (both valves closed.) Second, thread the tester into the spark plug hole for that cylinder and connect the regulated 100psi air source. Third, read the gauge on the tester.
If you are using 100psi and the tester reads 100psi, then you have 0% leakdown. 90psi would mean 10% leakdown, etc. Basically the equation is 100%-leakdown pressure/incoming pressure.
I would look for numbers in the range of 8%-10% as good.
Hope this helps.
Shane
Re: Leak Down Test? Also you should make sure that you somehow lock the motor also. Otherwise it may spin the motor slightly and change the test results.
Also check for air coming out of the radiator also. If your concerned about your head gasket at all.
Also check for air coming out of the radiator also. If your concerned about your head gasket at all.
Re: Leak Down Test? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by chasgiv3:
<strong>Also you should make sure that you somehow lock the motor also. Otherwise it may spin the motor slightly and change the test results.
Also check for air coming out of the radiator also. If your concerned about your head gasket at all.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Ooops, sorry I forgot that part... and yes this is a great way to check for blown head gasket or cracked head...
<strong>Also you should make sure that you somehow lock the motor also. Otherwise it may spin the motor slightly and change the test results.
Also check for air coming out of the radiator also. If your concerned about your head gasket at all.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Ooops, sorry I forgot that part... and yes this is a great way to check for blown head gasket or cracked head...
