The Novarossi R57HR 3D engine is ready to be pulled out of the author’s
Synergy N5c.
An oven mitt, heat gun, and zip tie are tools
crucial to removing a stubborn piston sleeve.
There are still plenty of us who enjoy flying nitro-powered helicopters. Yes, electric power is
clean, has more instant torque, etc., but
there is just something about the scream
of a nitro engine and the smoke. When
night falls, it gets even better.
Nitro engines in helicopters can have a
hard life, especially in 3-D machines that
run full throttle for most of the flight.
The only other part of the hobby I’m
involved in that similarly runs engines at
full power for the entire flight is Quarter
Midget Pylon Racing. These aircraft
often only run for slightly more than a
minute! We’re flying our helis for several
minutes at a time, which can definitely
be hard on the engines.
My Synergy N5c went through a
couple of Thunder Tiger . 56 engines (I
blew them both up) before I found a
good deal on a Novarossi R57HR 3D
helicopter engine at the Helis Over
Tidewater event in Newport News,
Virginia, in 2012. After my second
Thunder Tiger . 56 broke while at that
event, I bought the Novarossi, swapped
it with the Thunder Tiger, and haven’t
looked back.
I’ve flown my N5c hard throughout
the years, and the engine has never
skipped a beat. After flying it this past
summer, it started to feel like it didn’t
have the power that it used to, so I
decided to take it apart and inspect the
inside.
Disclaimer: I am not, and do not claim
to be, a nitro engine expert. What follows
is based on my own experiences through
the years. If you manufacture nitro engines,
or are a qualified expert on the subject, I
would love to hear from you.
The first step was to take the engine
out of the helicopter. Fortunately, the
Synergy N5c makes this an easy process,
and it wasn’t long before the engine
was sitting on my workbench. This
30% helicopter
fuel exclusively.
I checked the
compression and
the engine still seemed tight.
If you’re not sure how to check the
compression without the use of a gauge,
rotate the crankshaft (with the cooling
fan still attached to make it easy) and
feel how tight it gets as the piston
reaches top dead center (TDC) with the
glow plug still in. As you turn through
the TDC, the pressure will suddenly
release. If you can turn the crankshaft
freely without any or little resistance,
this is a good indication that there is
something wrong. If it’s smooth and
tight, you’re in good shape.
I removed the muffler, the backplate
on the crankcase, and the cooling head.
Helicopter engines are the ring-and-sleeve type. This means that the piston
has an additional ring around it. When
against the piston sleeve wall. It’s a
tight fit and is crucial to a good-running
engine.
Varying from engine to engine, you
should be able to pop your piston sleeve
straight up. If you are having difficulty
removing it, you can insert a plastic zip
tie into one of the exhaust ports. As you
rotate the crank, the piston will drive up
and pop the piston sleeve loose. If you
have an older, well-used engine such as
mine, you will need to apply some heat
to the crankcase.
Donning my wife’s best oven mitt,
I used my heat gun to heat up the
crankcase, moving the gun around it as it
was heating up. When it was sufficiently
hot, I gingerly did the zip tie trick and
the sleeve popped right up.
With the sleeve out, I was able to
97 Model Aviation APRIL 2017 www.ModelAviation.com
Engine checkup
Chris Mulcahy
cspaced@gmail.com
