Un d e r t h e C o w l
the owner won't allow you to pay for an internal inspection,
consider walking away.
"If the engine looks rough or is badly out of tune—you
may see exhaust system cracks and chafing, worn engine
mounts—it's probably been a shaker and won't be in good
shape internally, either. Ask the owner how he syncs his
carbs. 'Visual' isn't a substitute for 'vacuum.'"
Okay, You've Seen the Logs
You've seen the logs and checked for AD compliance and
made an overall external inspection. So far, everything looks
good. What now?
Have the owner start it. Is there water in the gascolator?
(Water, if it gets into the paper element of a fuel filter, can
create mush that can plug the carburetor jets.) Watch to see
that he checks the oil and that he "burps" the oil tank. What
is the idle rpm? If it's below 1,400, you can expect shortened
gearbox life; 1,800 or higher is okay. Brakes are cheaper
than gearboxes.
A proper compression check comes only with a warm
engine. Immobilize the prop with the piston at top
dead center (TDC) on compression and introduce air
at 80 pounds per square inch (psi). More than 25
percent leakdown demands a closer look. A simple
cranking pump test should give you 130 to 174 psi
(depending on model), with less than 30 psi difference
among cylinders.
Certain items are life-limited by hours. In the experimental
world, that's "on condition," but don't ignore anything.
Once wear starts, it can progress rapidly, and a failing part
can do a lot of expensive damage to "innocent bystander"
parts inside that engine.
Even when you get a good engine, treat its first run after
installation exactly as a new engine. Change the fluids and
use the right ones. Use unadulterated premium auto fuel,
and don't let it sit in your tank and carb bowl too long. Fly
it, for Pete's sake!
Mounting components too close to one another can cause interference and
damage in fight.
Absolutely, positively pay attention to www.Rotax-Owner.com.
Once you register, you'll get free e-mail notification of
all factory service bulletins and airworthiness directives
that might be released on it. The site's detailed videos
show how to perform many important maintenance and
tuning tasks.
Most importantly, as in flight, follow Cowan's maxim: Never
let a known problem continue. If you know something is
wrong, fix it.
For more information, register at www.Rotax-Owner.com. A
broad expanse of knowledge is there. The Rotax Line Manual
is available here.
Find ethanol-free gas (by state): www.Pure-Gas.org;
www.BuyRealGas.com.
A common failure happens when this temperature sensor melts or gets
crushed. It's easy to check.
36
Vol.2 N o.4 / A pril 2013
Tim Kern is a private pilot and has written for
more than 40 different aviation magazines. He
was a key builder on two aircraft projects and has
earned the title of certified aviation manager from
the NBAA.