Compression Test results?
12-29-2005, 08:40 AM
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Compression Test #'s? I am getting ready to do a compression and leakdown test tonight. I have been searching all over the place but have not found numbers to compair my results to. For example.. what would be bad, avg, good compression readings?
How is a leak down read? How many lbs of air do i put into a cylinder at TDC? Once i have air in there how do you measure leak %? Is is calculated over a period of time? Is a 98% leakdown good/bad 5%good/bad.
And from what i understand the following cylinders will be at TDC at the same time. 1&6, 8&5, 7&4, 3&2. Once you find 1&6 mark the 12oclock position on the crank pulley then rotate 90* gives you 8&5 at TDC, and so on...correct?
Thanks!
How is a leak down read? How many lbs of air do i put into a cylinder at TDC? Once i have air in there how do you measure leak %? Is is calculated over a period of time? Is a 98% leakdown good/bad 5%good/bad.
And from what i understand the following cylinders will be at TDC at the same time. 1&6, 8&5, 7&4, 3&2. Once you find 1&6 mark the 12oclock position on the crank pulley then rotate 90* gives you 8&5 at TDC, and so on...correct?
Thanks!
12-30-2005, 10:14 AM
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Originally Posted by Vertigo
I am getting ready to do a compression and leakdown test tonight. I have been searching all over the place but have not found numbers to compair my results to. For example.. what would be bad, avg, good compression readings?
How is a leak down read? How many lbs of air do i put into a cylinder at TDC? Once i have air in there how do you measure leak %? Is is calculated over a period of time? Is a 98% leakdown good/bad 5%good/bad.
And from what i understand the following cylinders will be at TDC at the same time. 1&6, 8&5, 7&4, 3&2. Once you find 1&6 mark the 12oclock position on the crank pulley then rotate 90* gives you 8&5 at TDC, and so on...correct?
Thanks!
How is a leak down read? How many lbs of air do i put into a cylinder at TDC? Once i have air in there how do you measure leak %? Is is calculated over a period of time? Is a 98% leakdown good/bad 5%good/bad.
And from what i understand the following cylinders will be at TDC at the same time. 1&6, 8&5, 7&4, 3&2. Once you find 1&6 mark the 12oclock position on the crank pulley then rotate 90* gives you 8&5 at TDC, and so on...correct?
Thanks!
if you're turning the crank 90* between each test make sure that you're testing the cylinders in the correct firing order (1-8-7-2-6-5-4-3). also, if you do not have the cylinder perfectly at TDC the compressed air will force the piston down. what we did at the school i went to was to put a long drinking straw in the spark plug hole and you see the straw stop moving at TDC. but remember that you'll be able to turn the crank shaft for a little bit before the piston will start traveling the opposite direction.
12-31-2005, 09:49 AM
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Originally Posted by 2000TransAmWS6
you're right, those cylinders are companion cylinders and will be at TDC (of their respective stroke) at the same time, but you have got to make sure that you're doing the test for each cylinder on TDC of the compression stroke, for the leakdown test.
if you're turning the crank 90* between each test make sure that you're testing the cylinders in the correct firing order (1-8-7-2-6-5-4-3). also, if you do not have the cylinder perfectly at TDC the compressed air will force the piston down. what we did at the school i went to was to put a long drinking straw in the spark plug hole and you see the straw stop moving at TDC. but remember that you'll be able to turn the crank shaft for a little bit before the piston will start traveling the opposite direction.
if you're turning the crank 90* between each test make sure that you're testing the cylinders in the correct firing order (1-8-7-2-6-5-4-3). also, if you do not have the cylinder perfectly at TDC the compressed air will force the piston down. what we did at the school i went to was to put a long drinking straw in the spark plug hole and you see the straw stop moving at TDC. but remember that you'll be able to turn the crank shaft for a little bit before the piston will start traveling the opposite direction.
