What is Compression Testing?

[The_Handier_Man1]

From: The_Pharaoh_Rulz_  (Original Message)
Sent: 12/8/2005 10:28 AM

What tools and gauges are needed?

How do you do a compression Test?

If the compression is low, what could be the problems causing it and what are the remedies?

- Sob



From: DampDude007
Sent: 12/8/2005 11:12 AM

All you need is a compression gauge,they run from $20 to $50 at NAPA,it has all the instuctions on the back of the package. You need to find out what the normal compression is for the motor,all cylinders should be close in psi,if you have a cylinder that is way low,it could be:
1.hole in piston
2.wore out rings
3.bent valve or cracked guides or wore out seats.
4.wore out cylinder wall,like some thing got in there and scratched it.
5. blown head gasket.

If all cylinders are unusually low ,it is just time for a rebuild,you can try puting in oil treaments all you want,those are just temporary fixes or they just mask the real problem.
Do you think you have a compression problem?
Dude



From: Im-still-Lefty
Sent: 12/8/2005 11:30 AM

A compression test, is a test of how well the cyl. are sealing. To perform the test, you will need a compression tester (available @ any parts store for around $30 bucks) First, remove all the spark plugs, then screw the special adapter that comes with the tester in the first hole & attach the gauge. Now, hold the gas pedel to the floor & turn the engine over a few revolutions. Take note of the peak reading on the gauge. Next, go to the next hole, & repeat until you have a reading for all 8 cyl. There shouldnt be any more than a 10% difference between any two adjacent cyl. nor, a 20% difference between the highest cyl. & the lowest, regardles of position. Now, after your first reading, go back & add 1 tablespoon of motor oil to each cyl., then do the test on each cyl. again. the reason for this is, if you have a cyl. read low, then add oil & get a higher reading, it pinpoints the problem to the rings not sealing, if the cyl. is low, and oil doesnt help, then it is either the gasket, or valves not sealing. there is also a similar test called a "Cylinder Leak-down Test" that is done much the same way, but it pressurizes the cyl. to a set psi. (usually 100psi) then you measure how long it takes the pressure to drop to 80psi in seconds, the longer it takes, the tighter the engine is. As an added benifit, you can use an automotive stethescope to listen at the rad. neck, intake manifold, exhaust pipe, and in each valve cover for the sound of escaping air, that way you know exactly where the problem is. A good repair shop can perform this test for around $80 bucks. It is the only "proof-positive" way to verify a blown head gasket or cracked head, or chipped/burnt valves without tearing the engine down.



From: lorielorief
Sent: 12/8/2005 12:47 PM

I would like to know the answer to this as well, because I'm looking to buy.

Lorie



From: denison
Sent: 12/8/2005 10:10 PM

I have done a compression test on my engine when it had been sitting for several months. I got some low readings when I checked it, after just moving it around in the driveway. After driving it for a couple of hours on the highway I did the compression test again. All of the readings on the low cylinders were nicely higher.
Therefore I wont assume its a big problem if I have low compression (like 80 psi versus the preferred 130 to 145 psi, on an engine that has not been run much recently.



From: cooneytunes
Sent: 12/11/2005 7:56 PM

Compression Testing is the process of how many Posts we can post on the wrong message boards, before SOB sends an e-mail....

Timmy



From: Enigma960080
Sent: 12/11/2005 8:07 PM

Thats  more  like a  leak-down test...   to see  how  much pressure he can  bleed off  before  he  goes  ballistic!