What you are looking for is the delta between the two gauges. Setting the first
gauge at 100 psi allows you to simply read the second gauge as a percent.
Example, If the first gauge reads 100 # and the second gauge reads 96 #, then
the leakdown is 4 %. If you only have say 80 lbs. of air from your compressor,
you will have to do some math to arrive at a percentage of loss. I have found
that a motor with gap-less rings will show 0 to 1 % leakdown if in good working
order. 4 to 6 % is not too bad. The motor needs work if you see over that. I
have tested motors with the piston in various postions in the bore looking for
scarring or bore scratches. I have had a fuel motor on more than one occasion
show good on the leakdown but the piston was melted down around the rings.
joe
V4GR@aol.com wrote:
> Keith; I don't know why but when I was going to A&P school we learned to set
> the gages at 80 lbs. Then we compared the reading on the downstream gage
> after opening the air valve. I seem to remember 20% for a worn cylinder cold
> was acceptable. More than that was not. Race motors should be much tighter.
> After the first few years at the airline we put away our leakdown testers.
> Couldn't get them to read correctly on a JT3. Rich
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