At 2:07 AM 12/11/96, Christopher M. Smith wrote:
>What is meant by a "leak down test" ?

don't know if your mechanic is using the correct vocabulary and is just
talking compression test or if he's actually talking about a true leak down
test.  leakdown testing is pretty rare among auto mechanics but is a
standard scheduled inspection procedure on recip aircraft engines.  Some
active A&P out there like Fred Dyen can correct me on the details -- it's
been a while i've been in the 100hr/annual insp loop.

the idea is to apply a given pressure in a regulated volume to a cylinder
and see how much of the pressure it maintains (ring and valve leakdown).
It's a great test. you can move the piston up and down in the cylinder and
see how well the rings are sealing along the stroke, not just at TDC.  it's
a lot more discriminating test than a simple compression test.

takes a 2 gauge setup (input pressure and cylinder pressure).  regulated
input air pressure is applied thru a calibrated orifice.  recollect it's
100psi applied thru inline .040" restriction and a good cylinder should
hold >~80psi of that.  same attention to cylinder to cylinder variation
applies.

toodles,
dwight

85GL
100K last week
1.9 heads/studs died @ 75K
2.1 swap
fire rebuild @ 90K