I am going to be doing a leak down test to find out the health of my motor and I am a little confused about getting each cylinder at TDC.. I think I have a good understanding about how to get #1 at TDC since there are marks on the gears. Rotate crank (clockwise) untill the marks line up, but how much do I turn the crank to get the remaining cylinders? To what I understand I would rotate (clockwise) it another 180 degrees to get #3 TDC, then 90 to get #4 and then another to get back to #2.. But that is what I read in another thread. I am also under the impression that the cam lobes must be at 11 and 1 oclock to ensure that cylinder is at TDC. If some one could confirm this or give any advice that would be great.

thanks guys,

--------chad-------------

 

umm.. not to say that you're not capable of this, but shouldn't a leak down test be performed at a qualified mechanic (not Canadian Tire hehe ))?

as for advice on the leakdown, i have no idea what a TDC is without googling it

 

I am sure I am more than qualified. If I installed my entire turbo kit with no problems, I am sure I am capable of this. Do you mean, what is TDC?(Top dead centre)? The only part I need help with is getting the cylinders at top dead centre. Other than than that it is pretty much the same as a compression test except you are pressurizing the system to see where the leakage is coming from.

PS: I wouldn't even trust CT to change my oil anymore

 

If you don't know what TDC is, then maybe you shouldn't be giving out car advice.

 

anyone??

 

Wait till turboslug or Kstokes logs on. They did the leakdown test on turboslug's S before he bought the car so they both should know how to do it.

As for me, I've never done a leakdown test before, so I would be talking out of my ass if I tried to give you advice.

 

Cool thanks man, any word from ur buddy BTW???

 

You rang?

When doing a leakdown test, being exactly at bottom dead-center really doesn't matter. You're really just looking to see if there is any valve leakage or gross piston ring leakage. As long as the intake and exhaust valves are both closed, the position of the cylinder in the bore doesn't mean much. It's wise to error on the "the piston is moving down" side of things as opposed to "the piston is moving up", to keep the engine from spinning backwards as you apply air pressure (sometimes it'll turn a few degrees.)

Just hook up the test rig, apply as much air pressure as your compressor can provide (100psi is a good number, and makes the percentage of leak very easy to figure out...), check the difference between both sides.

You can easily expect to see 3-4-5% leakage, that's pretty normal. If you're seeing >10%, something's wrong. Moreso, look for any gross variance between individual cylinders. If you see 3%, 4%, 3%, 5%, all is well. If you see 3%, 4%, 3%, 16%, be sure you don't have a valve part-way open. If they're closed, you've got a problem on your hands....

 

When you say both sides, do u mean I can check 2 cyinders at a time or what???

thanks

 

You can find the TDC by looking into the spark plug bore as you turn the crank or by sticking a long screwdriver in there and watching the handle movement. You can easily tell whether you're in the right stroke or not when you're doing the test, and once you got #1 figured out you can follow the firing order to speed up the entire process.