Mr.Chumchal

Alright guys I have a few questions on performing a leak down test and would like to get them cleared up before I attempt to perform one.

1.) What is the easiest way of getting each piston to TDC when I am doing a leak down test?
I was thinking once the spark plugs are out put a screw driver through spark hole, then crank over motor until screw driver is farthest out. If you know a better way please explain to me.

2.) What is a good amount of psi to pump into the cylinder?

3.) For a leak down test do I need to have the motor warm?

4.) Are these the correct steps: Make sure piston is at TDC. Pump air into cylinder. Listen for air leakage through oil cap, dipstick, throttle body, exhaust?

Exahust= Exhaust valves
Throttle body= Intake valves
Dipstick= Rings
Oil cap=?

Are these assumptions correct? (Oil cap= rings???)

Also anything else I am missing please let me know, thanks.

-Nick

Mr.Chumchal

Also does motor have to be at operating temps.?

Mr.Chumchal

One more question, does anyone know a easy and good way of locking down the motor once I get the piston to TDC?

peow130

Put the engine in gear, with the parking brake on..

not sure about the operating temp stuff
a leak down test just tests the PSI, and if the PSI is constant and doesnt change quickly then there are no leaks..

betelnut

Screwdriver is a good method, but when you say 'crank' I hope you mean by hand, not with the starter!

You need to make sure that it's at the end of the compression stroke/beginning of the power stroke; just TDC isn't good enough. You'll be close when the dizzy's pointing to the cylinder in question.

Oil cap and dipstick are really the same: you're listening inside the crank case, and yeah, that's where leakage past the rings would go.

Some other brainy fella here pointed out that you can open up the radiator and check there too if you suspect your head gasket.

betelnut

Yeah, I don't know about the other questions, just experiment. Don't think it needs to be hot, don't think it's sensitive to pressure.

Doubt 100 PSI are enough to turn the engine when the piston's at TDC.

Mr.Chumchal

"You'll be close when the dizzy's pointing to the cylinder in question."

^Can you explain this better I am a little confused? And yes when I say "crank", I mean with a hand socket.

betelnut

4 cycle engines, the crank turns 2x for every 1x camshaft revolution, so in a complete cycle you hit TDC twice, right? The "right" TDC is at the beginning of the power stroke, which is when the spark plug fires. Therefore the dizzy is an indicator of where you're at.

Pop the cap off the dizzy and see which cylinder the rotor's pointing at. Go to that cylinder and get it to TDC with your wrench & driver, do your leakdown. Turn the crank 1/3 revolution, lather, rinse, repeat. For hi-sheen hair with strength of hold, use LayRite Pomade.

Mr.Chumchal

This motor is the 3.0 V6, but I get what your saying kind of.

betelnut

Mr. Chumchal, methinks you need to do a little reading up on Internal Combustion Engines 101. Principles apply to all 4 cycle engines, no matter whether 6 cylinders (the one I described, hence 1/3 turn on crankshaft) or 4 cylinders. Good luck

Mr.Chumchal

7m4x4dude

a proper leakage tester will have two gauges on it and will hook up to a air compressor, you will need to regulate the air so you zero/max out the other gauge so you can tell how much air is leaking.


once the crank and piston are at tdc the air pressure shouldn't move the piston, but if the piston isn't standing on end or the rod it will sping over quick as . lol at least a 1/4 or 1/2 turn atleast .

betelnut

You funny, Gnarly4X

This reminds me of when I was about 17 doing the wheel bearings on the Datsun in my sig, pulled the rotor and couldn't get the outer race out.

Well, I didn't have a hydraulic press, so I took it to a machine shop and gave it to the old guy working there. He said, "my 3 year old grandson could do this!" He grabbed a big socket and the 3 lb sledge, and bam! bam! bam! it was out. I slunk outta there humbled like my mama had just scolded me.

Anyway, what's the best test for a pee-pee tuneup?

1stgen4gunner

Holy crap can I quote this!!