How do you check compression on a motor thats out of the car

[83Rabbit]

Im getting a 50k mile 2.5RS motor and its already outta the car, came from a running 2.5 with no problems, hes doing an sti swap. So how do I check the compression? Its without the tranny, so cranking the starter is out.

[CaptainHenreh]

Im getting a 50k mile 2.5RS motor and its already outta the car, came from a running 2.5 with no problems, hes doing an sti swap. So how do I check the compression? Its without the tranny, so cranking the starter is out.

leakdown tester, maybe?

[NTIman]

leakdown is the best,not only can you tell if there is any problem,but where it may be.

[JohnC]

You can always just attach the starter, and jump it.

[.RJ]

turn the crank by hand....

[white_2kgt]

You can always just attach the starter, and jump it.

that's what I did when I bought my cobra engine. I took a starter and a battery with me and hooked the batt directly to the starter, turning by hand won't give you consistant enough reading

[83Rabbit]

ok, so when I go pick up the motor, how can I take a portable leakdown system with me? Whats involved? What do I need? Thanks!

[NTIman]

for a leakdown test you need
-a leakdown tester (available through summit, snapon,etc...)
-at least a 100 psi air pressure source.
-a ratchet with socket to fit crank bolt
-a ratchet to remove plugs

the process is very simple
1. place number one piston at exactly TDC (middle of TDC dwell,where the rod centerline is parallel to the cylinder wall) If the piston is not there,the engine will turn over
2.hook up tester to the air hose with at least 100 psi
3. put hose in plug hole,and the other end in tester
4. Dial pressure up to 100 psi on first gauge
5. take reading on second gauge,which should always be lower
5. Rotate the engine so the second piston(in firing order) is exactly at TDC and repeat process for each cylinder

Listen to the intake to check for intake valve leakage
Listen to exhaust to check for exhaust valve leakage,
Listen to cooling system hookups for leaking headgaskets and/or cracked block or head
Take off the oil cap and listen there for excessive leakage in case rings suck

There will always be leakage past the rings,but should not be much.
To get percent of leakage subtract the number from the lower gauge from the higher reading.
Great condition 5-10%
Good condition 10-20%
Bad condition anything over 30%

Those numbers are just a basic idea for what to look for.

Most importantly, Always take the ratchet off the crank bolt before hooking tester to engine. Its never good to be nut checked while working on an engine.