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1. 05:23 AM - Re: Compression values (Noel Loveys)
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| Subject: | RE: Compression values |
Martin:
The standard automotive compression tester is about as useful as chewing gum
in the gas line. They lie! Actually they lie like troopers after a bad
day!
The only compression test worth looking at is a differential compression
test. This is done by flowing 80 psi of air into a cylinder at TDC and
checking how much pressure is lost in that cylinder. A perfect score would
be 80 and lesser scores would be in the seventies you will have problems in
the mid sixties. ( sounds familiar doesn't it ;-) )
The differential test is as close as you can come to testing the cylinder in
operation. It has the added abilities to accurately find where the problems
are... If you head air leaking form the engine base then you have bad rings
on that cylinder, If it comes from the intake manifold it's the intake valve
and of course if you hear hissing at the exhaust the exhaust valve will need
work.
To do the differential test you will have to remove plug from each cylinder
just as you have to do with the automotive tester. While you are doing this
it's a good time to have a nice close look at your spark plugs. Cylinders
suffering lower compression may also display a bit darker plug as the fuel
doesn't burn completely in the cylinder.
Getting a differential test done on each annual would be a good idea just
the same as cutting open oil filters and looking for large metal flakes.
Hope this helps.
Noel Loveys, RPP, AME intern
Campbellton, Newfoundland,
Canada
Kitfox Mod III-A, 582, B box, Ivo IFA
Aerocet 1100s
noelloveys@yahoo.ca
> Time: 03:28:48 PM PST US
> Subject: JabiruEngine-List: compression values
> From: "avidflyer01" <vegayacht@club.fr>
>
>
> hi folks,
> I would like to find out what are typical compression values on a
> recent 2200; could those who measured their compressions give me their
> results, together with approx engine hours and age?
>
> as I have a problem with a leaky valve in one cylinder I carried out
> some serious tests on my engine and found that on the three "good"
> cylinders I have only 122psi (8.6 bar). I've heard about one engine
> that at 300hrs had as much as 160psi (11.2bar), yet I also heard that
> my 122psi is a reasonable compression.
>
> My compressions were taken with a warm engine, one sparkplug per
> cylinder removed, throttle fully open, good battery. Engine has 100
> hrs, 2 years old (hyd lifters).
> I also did a leak down test: pressure drop on good cylinders were 9%,
> 11% and 14%; it was 35% on the bad one.
>
> thanksfor your help
>
> Martin
> Avid Flyer / Jab powered
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