Engine Break-In

How and why should we break-in our new helicopter engines? That is the most common question asked by everyone who buys a new engine. The responses to both of those questions are somewhat controversial, and everybody has their own method and reasoning for how and why. Just a few weeks ago, I had a hot and intense debate with a fellow RC heli pilot who happens to build full-size car engines for a living about this very topic. The conclusion that both of us came to was that a new engine needs the piston and ring to seal properly, and therefore you need to break in an engine. If you do not break in a new engine properly, you reduce its power and life.

What do I mean by sealing the piston and ring? Well, when you look at an engine sleeve with the naked eye, you see a smooth shiny surface. You see the same thing in the ring and piston, but if you ever look at these three components under a microscope you will see something completely different. You will see valleys, peaks, grooves and imperfections on the ring, piston, and sleeve. During the break-in process, oil will get in these grooves and valleys to allow the ring to glide over these areas as the piston and ring go up and down in the sleeve. While this is happening, the peaks and imperfections are being smoothed out in all three components. This is the goal of breaking in an engine: to create the largest possible surface area of contact between the ring and sleeve. So why do you say this is necessary? Well, the answer is simple. A properly sealed engine will produce maximum power with the least amount of fuel consumption. When the piston and ring have properly seated, they do not allow combustion gases to escape from the combustion chamber into the crankcase where that energy ends up going to waste. In addition to the previous statement, an improperly seated ring will allow too much fuel to get into the cylinder and the excess oil and fuel will be pushed out of the exhaust port, causing the engine to run improperly due to the fuel not burning completely. This, in my opinion, is one of the reasons why people have tuning issues with their engines.


The Basics
To break in an engine I usually fire up the heli and let it idle for one tank's worth of fuel. I keep it as rich as possible to allow for extra lubrication. The reason for this is while the ring grinds away any imperfections, I want the metal debris to be ejected into the exhaust port easily so that I do not have any unnecessary scarring of the sleeve which could reduce compression. The extra oil will also help the engine cool while it's sitting on the ground idling. Once the first tank is almost empty, I shut off the engine and let it cool. During the cooling phase I make sure the piston is at the bottom of the sleeve. This way when the ring cools, it can go back to its normal shape as there is less compression at the bottom of the sleeve compared to the top section. Tanks two through four are just hovered with the engine still running rich. After every tank I make sure the piston is at the bottom of the sleeve during cool off. During break-in, I also check the temp of the engine to make sure it isn't running abnormally hot. For tanks five and six, I lean out the engine just a bit and do some casual forward flying. Once this has been completed, I tune the engine to my liking and consider the engine to be properly broken in.


Step-By-Step Engine Break-In
Step 1: Install a new glow plug in the engine.


Step 2: Fuel the heli with your pump, but make sure to close the end of the fuel tubing leading to the engine with some fuel line clippers. You do this to keep the engine from flooding during the fueling process.


Step 3: As a general rule, you can start with these settings. Close all needle valves and open them back up by turning the high end needle counter clockwise by two full turns, and open the low end by 1 3/4 turns. If your engine features a mid-range needle, it should also be two turns out. This should be a good starting point, but make sure to consult the manual that comes with your engine for specifics. You will adjust this as needed later.


Step 4: Turn on the radio and heli, and make sure that the carb is in the fully closed position while the throttle stick is in the down position.


Step 5: Prime the engine by unclipping the fuel line clipper and turning the engine over briefly without the glow igniter plugged in.


Step 6: Hold the heli by the rotor
blades and put a foot on the skids. Connect the glow plug igniter and start the heli using your starter.


Step 7: Once it has been started, make sure the engine will idle on its own when the igniter is removed. Let it idle like this and use your temp gauge to monitor the temp of the engine. With the settings above, the engine should be relatively cold.


Strep 8: When the first tank is 90% empty, shut off the engine by pinching the fuel line leading to the carb and let the engine cool down. Make sure the piston is sitting towards the bottom of the sleeve during cool down.


Step 9: For the next 3 tanks I start the heli using the above procedures and I begin to hover the heli. If the heli dies when idling, I lean out the low end needle by turning it 1/8 of a turn clockwise.


Step 10: On the 5th tank I am ready to lean out the engine. I turn my low end needle in 1/8 of a turn at a time until I can pinch the fuel line for at least 7 seconds before the engine dies. On the high end, I lean it out enough so that I still see a nice smoke trail during hover.


Step 11: After the 6th tank, lean out the high end a bit more but keep the smoke trail visible. And then have fun!

Note: Some engine run hotter than others, some run best below 200�F while still others may get up to 260�F or more before they make power. Consult you manual for specifics.

CONCLUSION
I do this to all my engines. I have an O.S. 50 that I've had for almost 3 years; it was originally bought for my Hirobo Evo but now resides in my Raptor. It gets about 6 flights per weekend and the engine still runs great. I opened it up this past weekend just to look it over and all seems good. So if you take the time to break in your engine properly over the course of the first few tanks, it should give you long lasting flying enjoyment for years to come.