Leak Down Test - So close to perfect! Except for cylinder 3
 

Hi Team,

Just completed a leak down test, seeing as I had the intake system completely off and am waiting for parts. Engine runs well but just wanted to see how close I am to a rebuild.

All Cylinders but cylinder 3 showed good results around 4 to 6%. Cylinder 3 is at 15% 😞

Definitely the intake valve as I could easily hear the hiss with the intake removed.

Worth checking intake valve clearance on that cylinder? Could it be carbon build up on one cylinder?

Any suggestions as to why I have one dodgy intake valve?

Thanks

Lots of possible reasons. It's worth running the car and measuring cyl 3 again to see if it improves. In case it's just carbon, that would get rid of it.

If you had the intake off, it's likely that a little piece of something is stuck between the valve and the seat. Rotate the engine around until the intake valve is open, then blow compressed air into the spark plug hole (or vice versa, blow through the intake port and let it come out through the spark plug hole), then retest.

With the valve cover off and air pressure on #3 during the leakdown test, take a plastic hammer and bip the adjustment screw on the rocker several times and see if things improve.

15% leak down alone is not worth doing a valve job. Unless, of course, you are into perfection then spend away.

I agree. Lots of the ones we test have a little carbon hanging things up. Do what’s suggested above and retest.

Hi Team,

Thanks for the input. I opened the valve and cleaned around with a soft toothbrush and also blowed compressed air through.

Leak down went from 15 to 9%. So I am guessing still a little more build up I need to remove.

Happy enough now that the engine is in good condition. Will blow a bit more today and see if I can dislodge more.

Ok, thanks everyone again, just blew it out and gave it another clean. Bang on 5% like the others! Now to rebuild the intake and get on the road!