How to "run in" an OS50/OS55 Engine

New engines are not ready to be thrashed in Idle Up or Stunt mode
(Also applies to old engines with a new ring/piston/liner)
A new engine needs to be put through a short and simple "run in" procedure
(The American's call this procedure "Break In" but I dislike the term "Break")
The "run in" procedure introduces new metal engine parts to each other and allows them to "mate" nicely
OS engines require minimal "run in" time - you can complete the process in 3 flights

Generally new engines come with oil over the engine internals
If your engine has been sitting unused for a long period of time and is rather "dry"
a nice thing to do is put a few drops of fuel into the engine via the glow plug or exhaust.
This provides lubrication during cranking and starting...

The OS55 has two needles and a screw
The needle above the fuel inlet hose is the main needle (also called the high speed needle)
The other needle is the mid range neddle

The idle mixture is a screw (which drives an elipical cam)
The idle mixture should almost always be left at the stock setting
which is the slot in the screw is in line with the bolt holding the brass plate
(There are times when it's advantageous to have the idle mixture a tad rich)

The main needle controls total fuel flow into the carburator
You mainly tune this needle based on the engine needs and performance in idle up (stunt mode)
This is why it's also called the high speed needle
At lower engine rpm/speed the fuel mixture is better controlled by the mid/idle settings
But you have to get the main needle right first
Changing the main needle setting alters the fuel delivered to the mid & idle circuits
If you don't follow a process you can end up changing needles forever and getting frustrated
Get the main right, then fine tune the mid - seldom need to mess with the idle

The carburator settings for initial run in are the default settings in the manual
For the OS55 this is 2 turns out from fully screwed in - on both the mid and high needles
(This is likely to be excessively rich - 1.5 turns on the mid may be better)

Gently screw the needles in by hand until they are closed
Do not use force, that will damage the needle tip and alter tuning and performance
Then rotate the outer keeper until it's in line with the slot in the needle
This is used as your tuning reference point
Now turn the needles out, with every half turn, the needle slot will align with the keeper
This makes it easy to spot 1/4 and 1/2 turn needle positions

When running in an engine you do not want the engine to be "slobbering rich" (like Bill Gates)
This will prevent the engine of getting up to a useful operating temperature
and make operating the engine/model very difficult
The general rule of thumb is to run the main needle either 1/4 or 1/2 turn richer than normal

Running in an engine requires the engine operating at a nice temperature
This temperature will be lower than normal but not excessively cool
The lower temperature is achieved via slower RPM and lower workload
Running in an engine requires a mild and varying workload (varying RPM also helps)
Making the engine do work puts pressure on the ring against the bore
This encourages the new metal parts to mate and get used to doing useful work
We do not want to subject the engine to full throttle during run in
We do not want to run the engine at excessive RPM (stay under 2000 rpm headspeed)

The run in process is also about putting the engine through heat cycles
Don't immediately refuel and fly again, let the engine cool down

I like to do the very first flight on a TX throttle curve rather than a governor
This enables more RPM variation to be used (the governor will run a constant RPM)
When running in an OS50 or OS55 I tend to use the following throttle curve: 0 28 38 48 100
After the run in process when you've leaned the engine out this should be reduced to 0 25 35 45 100

So, you're ready to start your new or rebuilt engine
(Make sure you have a new OS8 or Enya3 glow plug)
If you have a pumped or regulated engine it may be helpful to
use full throttle with the glow plug OFF and crank the engine over
This will build up pressure in the tank and bring the fuel up to the carb
(This is where we need that internal lubrication!)
Then close the throttle, turn the glow plug on, crank and start the engine

Most likely the engine will start and then die immediately
due to being new and rich and the idle trim not being right
Increase the idle trim and restart the engine

The next most likely problem
is the engine dying as soon as the glow plug power turns off
That's due to the engine being very rich and snuffing out the glow plug
Increasing the idle trim should help
alternatively close the main needle by 1/8 or 1/4 of a turn

Your next problem is spooling up
With a rich setting this adversely effects the low speed performance
and makes spooling up difficult, the engine may cut
Just restart and spool up slowly,
once you get past the ~20% stick position it should spoolup fine

Take off into a hover and let the engine and carb warm up for 20 to 30 seconds
If the heli is wobbling or nodding that means the headspeed is too low
Raise your throttle curve a little to address this
There should be plenty of exhaust smoke
(unless you are using thick oil like CoolPower Green)

Next go into forward flight and do simple figure 8 circuits
You can gently build up quick forward speed and use a significant banking angle
Don't use full collective however, ~80% should be your maximum
Mild stall turns are also useful for putting pressure on the ring
Mild climbouts are also useful (do not bog the engine)
Just fly around putting mild and varying load on the engine

At the end of the first flight let the engine cool down
If your fuel tank is exhaust pressurised always refuel immediately
This pushes the hot and toxic exhaust gas out of the tank and makes the clunk line last longer

When you start the engine for the 2nd time you will notice that it starts easier and is more willing to idle
This is a clear indication that the run in procedure is working correctly
You will notice a further improvement in flight 3

In the 2nd flight you do more of the same, perhaps applying a little more load this time
Again, after the flight, let the engine cool down.

In the 3rd flight you can go into a idle 1 (stunt 1) with a reduced headspeed setting
Something in the 1800 rpm to 1900 rpm range would be good
Again, fly around making the engine do useful work with a varying workload
At this stage you can certainly do extended climb outs (longer/higher)
but don't use full collective (perhaps ~90% now)
Again, after the flight, let the engine cool down.

Once these three flights have been completed you can return to normal operations
You will re-tune the engine for normal operations (see how to tune article - coming)
You will lower your normal mode throttle curve
(because the engine will rev harder when you lean out)
You can use idle up (stunt mode) and go 3D

Enjoy...