The Engine Shop-2012/04

www.ModelAviation.com April 2012 Model Aviation 77
electrics
Greg Gimlick
THE ENGINE SHOP [email protected] Henderson
[email protected]
Engine servicing, part one: As
I write this, it is winter in the
Northeast. Time to pull some
engines apart! It is surprising to me how
reluctant people are to do this.
If an engine is still under warranty,
it’s best to call the supplier, get a return
authorization, and ship it back; however,
if the engine is old and no longer
covered, then why not “have at it?”
Digital cameras are a good aid in
this endeavor. Take as many digital
photographs as you like. It costs you
nothing to take one or even 100. My
iPhone 4 is always by my side. It is easy
to use and allows me to review photos
quickly. It is also great for blowing up
small details at the touch of a finger;
expensive 35mm developing or PC and
printer aren’t needed.
You don’t need many tools, and as a
modeler you will likely have most of
them. Some tools may seem a bit exotic
at first, but there are cheap and easy
alternatives. You will usually need some
metric Allen keys, a Phillips screwdriver,
and a foot-long piece of a 2 x 4. The
latter you will use as a hammer or a
base block. I will explain later.
At some stage, you will need heat to
remove bearings or stubborn cylinder
liners. Most of you have an oven
(convection type—not a microwave!).
If you do not have access to an oven
(some don’t understand the need to
cook a crankcase at 400° F for 30
minutes) you can use an iron-oncovering
heat gun.
In many cases, the problems with an
engine are either bearings or piston/
liner issues. Diagnosis is often best
achieved by taking the engine apart. As
an engine fanatic and columnist, I often
take engines apart (and put them back
together again). I have not forgotten
the first time and the associated
trepidations. Maybe this month’s
column can help you through those
moments.
Choose a good place to do the job,
preferably where you can leave the
pieces setting while you order new
parts. A soft
carpet under
your chair will
save a crankcase
fin or two if you
drop the engine.
Servicing Your Engine
To change bearings, you need to take
the motor completely apart. The heat
that you will apply to the crankcase can
damage parts such as carburetors.
It is a great idea to grab a few used
food containers to capture the parts
as you disassemble the engine. You
can label these containers with names
such as carburetor parts, head parts,
backplate, piston liner, etc. It is also a
good idea to take photographs as you
take the engine apart.
Before you begin, clean the motor
and remove the plug, needle, propeller,
washer, and nut. Then, take a picture.
You may need it later to guide you in
putting the head or carburetor back on
the right way.
Begin by removing the carburetor,
which is usually held on by one pinch
bolt or two screws on either side of the
crankcase. It might not seem necessary,
but you will be heating up the motor
to loosen the bearing fit and the O-ring
fuel seals will need to be protected.
Next, remove the backplate. Keep the
screws and the backplate together. The
screws are often a specific length and
should not be mixed with the rest of
RIght: Here is a “denuded” O.S. 1.60 ready for
disassembly. The external parts were removed with
two Allen wrenches and a Phillips screwdriver.
Left: You don’t need many tools to tear down a modern engine. As
a modeler you will likely have most of them. Taking photos along
the way can make reassembly easier.
PLUS:
> Vintage engine
photo answer
78 Model Aviation April 2012 www.ModelAviation.com
THE ENGINE SHOP
of the cylinder. For a six-bolt head,
the formula is to tighten diagonally
opposite. The head may still be a bit
tight, so a light tap with the 2 x 4 will
do the trick. Caution: Avoid hitting
the cooling fins.
Many engines have a propeller
driver that pulls off easily. There
might be a Woodruff key that stops
the propeller driver from rotating.
Look for it and for a washer that is
found between the propeller driver
and the front bearing. It is important
that this washer goes back there later.
is all shiny and new looking in there,
then the bearings and crankshaft are
probably okay.
It is time to loosen the head bolts
roughly a half turn all the way
around. This prevents warping of the
aluminum cylinder head because of
uneven bolt-tension removal. With
five head-bolts or more, you should
loosen each one in an opposite
pattern.
Each time you loosen a bolt, move
the wrench over the glow-plug
hole to the bolt on the other side
the screws. In most cases, you will find
a gasket on the backplate cover. Keep
this gasket in one piece.
It is a good practice to fit new ones,
but you can save the old one with a
razor blade slid and worked between
the mating faces. (Note which way up
the backplate is fitted. There is usually
a cutaway to clear the piston skirt.)
You are probably asking, “What
should I be seeing?” Most of the
engine information you need will be
inside the crankcase. If you see much
rust, the bearings are likely shot. If it
“Mommy, look what I did!” It only took 6 minutes to take the “bare”
engine apart for this photo.
Right: Most good engines will have a phosphor bronze
bearing pressed into the connecting rod. This bearing will
usually have a forward-facing chamfer on the edge.
You can remove the
cylinder liner with
your thumb inside the
liner to get some grip
on the exhaust port
and the cylinder walls.
If the propeller driver does not pull
off by hand, then you need to employ
a “puller.” Inexpensive ones can be
found at any automotive store. They
are used to remove corroded battery
terminals. Do not get too enthusiastic
and whack the propeller shaft with
your 2 x 4! You need to remove the
piston assembly first.
Remove the cylinder liner. This will
give you the “play” so that you can
take out the piston and connecting
rod. Put your thumb inside the liner
to get some grip on the cylinder walls
and slide out the liner.
If it refuses to budge, warming
the casing with a covering heat gun
will give quick results after you have
removed your thumb. (Please note
the word “covering” before heat gun.
Do not be tempted to use the paintstripper/
remover heat guns available.
They get too hot, will burn you, and
will distort the crankcase.)
Remove the piston and connectingrod
assembly by taking them out as
one piece. Usually, there is no need to
disassemble the piston and connecting
rod. The end of the connecting rod in
the piston should slide to the rear of
the piston on the wrist pin, aka small
end. If the connecting rod will not
move back, thread some dental floss
around the piston wrist pin to clean it.
With the connecting rod moved
back, it should come off the
crankshaft pin, aka the big end.
Sometimes you have to jiggle it a little
and twist the crankshaft a few degrees
either way. The piston may have a
ring. You don’t need to remove it yet.
Many engines have a phosphor
bronze bearing pressed into the
connecting rod. This bearing will
often have a chamfer on the side that
faces forward to meet the flywheel
portion of the crankcase.
Now you can finally tap out the
crankshaft with the 2 x 4. This 1-foot
piece of wood has the right mass to
move the shaft without damaging the
threads. Do not put the crankcase
down on a hard or metal surface to
do this because you could damage the
backplate mating surface. You can also
now use the 2 x 4 hammer method to
loosen the drive washer if it is stuck.
At this stage you have removed
everything except the bearings. Taking
a picture of the bearings before
and after removal can help with
identification and orientation later
on. The numbers that you will see
identify all bearings and are necessary
to order new ones. You can always
order from the original manufacturer.
I always order from Boca Bearings
and replace the front and rear every
time—even in new engines—with
stainless steel versions.
Heat up the crankcase to make it
easy to remove the bearings. Heat the
engine for roughly 20 minutes in an
oven at 350° to 400° F. You can use a
covering iron heat gun, but you must
evenly distribute the heat to avoid
distorting the casting. I have even put
the crankcase on the back wire cage
of a barbecue grill for 10 minutes to
do a bearing change at the AMA Nats!
(This is not recommended. It will
draw a lot of abuse from the queue
you jumped, and also several requests
for “one of those with ketchup!”)
With crankcase preheated, the
easiest way to remove the rear
bearing is to tap the back of the
whole casing firmly on your favorite
wooden block. You will need some
oven gloves—preferably not ones
you intend to return to the kitchen.
The main bearing will fall out. If the
bearing does not move at all, heat
the casing again for another 10
minutes.
The aluminum casting expands
much more than the steel outer ring
of the bearings. The bearing will fall
out or move with the gentle tapping
or poke of a wooden dowel.
Now you have taken your engine
apart. In part two, I will address
carburetors, the secrets of what
to look for regarding damage and
problems, and how to successfully
put it all together.
Photo Question
Thanks to everyone who wrote to
me about the vintage engine photo
question. I received 39 emails—an
outstanding response from you old
engine lovers. The first correct answer
was from James Larkin, who saw
a Super Cyclone, Ohlsson 60, OK
Herkimer 60, and a Foster 99. All of
you clearly have a passion for these
lovely pieces of engineering from the
past.
It was suggested that I make the
question harder and rarer. I wonder
if I will ever feel this way about my
OPSs, Rossis, Enyas, EDs, Mercos,
O.S.s, YSs, and Mokis, to name a few.
Happy New Year to all you motor heads
from [email protected].