Compression tester

[Hawk]

I found a s38 cheap in a wrecked car. I want to do a compression and leakdown test. I got a compression guage to check it. I just want to know the proper method for using it. Do you just put it in and crank? ot use Tq wrench to take each piston to TDC? Any help would be appreciated!

[rs4pro3]

remove all spark plugs, and disable the fuel system, then crack the throttle fully open, thread the tester into the #1 plug hole, and crank it over. Then do the same for the next cylinder and so on.

[StereoInstaller1]

Exactly as described above.

Leakdown is a far better test for ring issues, but requires compressed air and a different set of guages.

If you find low compression, squirt about a teaspoon of regular motor oil in the cylinder then re-test. This will show bad valves or not.

Luke

[FredK]

When you are testing compression, you need to crank the engine over 3-4 times for each cylinder, so you need a pretty healthy battery to complete all of the testing. If you have low compression on a few cylinders and you have to test a second time after dripping in a teaspoon of oil into the cylinder, you will almost guaranteed drain the battery. Have a battery charger handy too.

Make a note of how quickly the engine builds compression. It should do it quickly, ~75-90 psi on first crank.

[91Saleen#15]

When you are testing compression, you need to crank the engine over 3-4 times for each cylinder, so you need a pretty healthy battery to complete all of the testing. If you have low compression on a few cylinders and you have to test a second time after dripping in a teaspoon of oil into the cylinder, you will almost guaranteed drain the battery. Have a battery charger handy too.

Make a note of how quickly the engine builds compression. It should do it quickly, ~75-90 psi on first crank.

It's important to use the battery charger the whole time. If the battery loses power and turns over at a slightly slower rate on the last cylinder tests, the readings will be lower. I try to minimize variance the battery voltage during the test by using a battery charger that can supply starting amperage (i.e. not a trickle charger)

[Axel]

also dont forget that you are only allowed a maximum of 10 psi. varience between all your cylinders.
if you have more, then have the engine checked out. you could be looking at needing to do a rebuild or a machine job.

[StereoInstaller1]

Not 10psi, but 10% variance.

Luke

[Axel]

Thats true i had just went back through the book and caught myself on that.
keep that in mind Hawk, other wise you will end up with a situation I went thrugh just recently! NO FUN- let me tell you!