rehn@rockisland.com wrote:
> I recentlty purchased a differential pressure guage to measure pressure in the
cylinders. I have read the directions and am looking for those of you experts
out ther that have experience and that might give a step by step on the use
for our rotax engines. Like pressures to set the guauge that has pressure
delivered
to via the outside pressure and what to look for in the other guage . What
noises if any when the pressre in clyn. reaches it max and what gauges are
doing etc. I guess i'm looking for a step by step.
Pressure in is 80 PSI; pressure on the other dial is your reading. If readings
good, say above 70 PSI, what and where you hear anything doesnt matter. I think
both Continental specify 60 as fail.
The trick is to get an accurate reading if really important, as you pull the
piston
up to TDC and stop it at perceived TDC. Its easy to cheat a reading, and
you can also change the seating of the rings giving a false, low reading. Never
done it on a Rotax, but working the prop (safety first in working that prop
if she should get away!) through a reduction gearbox + backlash may be
interesting.
If elusive to you, maybe you can practice on somebodys direct-drive Lycoming
or Continental. Or ask a maintenance shop when they might do this task
and just watch.
If you're working alone, I recommend you reduce regulated 80 PSI in a bunch,
before
disconnecting the tester. Theres hair-trigger pressure on that prop, more
so Id guess through a redux drive in reverse.
However, whether a reading you get, verses an experienced aircraft repairman may
get, is 72, or 78 really doesnt matter. Engine should be at least warm when
you do this, though not always mattering that much. Fly one hour off and upon
landing, repeat test and even get some other significantly different reading.
Im surprised Rotax specifies a direct compression test primarily. Ditto for my
newer Toyota Solara, rather fancy engineering. Not precise, and too much noise
going on for even a helper to detect by sound at appropriate ports a leak past
rings, intake valve, or exhaust valve. Have fun!
Fred F.
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