cylinder leak down test

beauchemin

beauchemin

Senior member
Location
Victoria, British Columbia
I'm quite excited, but my wife thinks I'm bonkers!  I got 88/90, 89/90, and 89/90.  This is on a cold engine (at TDC), since the ignition is currently fried.

One question:  Would I expect to get better or worse readings on a warm engine?
 
Is that a Leak Down or Compression Test?

Generally a Leak Down Test is described as done when a Piston located at a Specific Degree ATDC say 15, 30 or 60 Degrees with the Crank Locked. Then say release 140 PSI into the Cylinder through the Spark Plug Hole and with both Valves Closed, TIME is MEASURED for the Pressure to leak down to say 30 lbs. This time is compared to other pistons locked in the same position. Leak Down Tests can point out specific issues: Bad Valve Seats, improperly Set Tappets, Worn Rings, Cracked Pistons/Bores/Heads and Casings, Blown Head Gaskets ...etc.

Generally you only want to hear air escaping from the Crank Case Vent during a Leak Down with the longest time possible.
 
OK that's another method where time is not taken into consideration.

You are keeping the Valve Open to the Compressor Reservoir and the method I describe leaves the Compressor out of it. Hard to say which method is more advantageous but I would imagine leaving to compressor out of the equation would give you a better diagnoses of the Compression Cycle by Measureing the Time the air leaks down between 2 Pressure Points in the Cylinder.

It will be interesting what others have to say.

I suppose both methods have an advantages over the other depending on what you're after.
 
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