BOTTLEDZ28

iTrader: (9)

Im gonna do a leakdown test on my engine this weekend to try and trace down my blowby. I just need some tips from those that have done it. I did a few searches on the net and some say to remove all the plugs while others say to only remove 1 at a time. Whats the best way? Also, the directions I have read seem simple enough but is this basically just injecting forced air into the clyinder and waiting to see if it leaks out anywhere. What do you do, just connect all the lines and gauges and then turn the valve on to allow the air to enter the engine?

oh is there anytime in an engine where 2 cylinders are both at tdc at the same time? I ask because then it would a little quicker to do this test.

Dialed_In

iTrader: (3)

Pull the spark plugs out. It'll make it easier to turn the motor over. Start with no. 1 cylinder and bring it to TDC on the compression stroke so you know the valves are shut. Try to stop in a couple degrees before TDC otherwise the presure is going to try to push the piston back down. Thread the hose into the plug hole then hook up the air line. Turn the dial until you have 100psi reading on the first gauge. Then read the second gauge. If you have 100psi going in and 98 going out then you have 2% leakage. Repeat for every cylinder. Rotate it by hand. Thats why having the plugs out makes it easier.

BOTTLEDZ28

iTrader: (9)

thanks. is there any tricks to doing 2 cylinders or something and not rotating the engine. Is there any pistons in the engine are are both at TDC at the same exact time?

CrazyHawaiian

Well you should want to rotate it because you want to watch the psi readings as the piston moves and intake/exhaust valves open and close. This is why the leakdown test is so much more precise than a regular compression test. Instead of just 1 reading you're getting readings while the piston is moving and stuff, you get a better idea of whats going on.

Dialed_In

iTrader: (3)

not to mention the opposing cylinder is going to have an open valve.

BOTTLEDZ28

iTrader: (9)

I just bought a dual gauge Proform Leakdown tester and will be doing htis test on Sunday. Hope everything does well. I will post results here.

ZZ28ZZ

You're not supposed to try turning the eng over while a cyl is pressurized. Once the crank/rod angle gets to certian a point (not very far from stright-up), the eng will rotate rapidly on it's own due to the compression. It's a good way to get your fingers mangled.

Many years ago, I was doing a blow-by compression test on a small aircraft. We didn't have the crank at just the right spot. A few seconds after the air was introduced into a cyl, the prop swung around and hit my buddy in the back of the head. He couldn't stand up for hours after that.

You will never have 2 cyls at tdc on the compression stroke at the same time. Follow the firing order from one cyl to the next. This will save you a lot of manual eng turning.

BOTTLEDZ28

iTrader: (9)

thanks. the only part of this job thats gonna slow me down is the simple part of finding TDC on the CS. I can remember which blaancer I installed and I hope it has marks all over it. I read soemewhere that this help pin point TDC when moving to the next cylinder or soemething. Im still reading directions on it now though.