Engine Break-In
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Question: How do I break in my Jett?
Answer: There are more ways than one, but it is important to remember one thing: With an ABC or AAC engine you don’t really have to worry about breaking in the piston and liner as that will take care of itself. The rod and crankshaft journal pin fit is the object of the break in.
Jetts are tight coming from the factory. It has always been a source of annoyance for me to buy a new engine and find that it is already too loose, even before it has been cranked up! ABC and AAC engines run better and produce more power when they are tight, and by the time there is no "pinch" left (bump at top dead center) the engine is starting to lose some of its power. So if your engine is "too tight" coming from the factory, be happy that you are getting your money’s worth in life and power. More of this is in the "my engine locks up" FAQ.
Breaking in your Jett: Put your engine on a test stand!!!. You pay a lot of money for your engines and airplanes. You must spend a bit more time and money to get the engine operating well before you fly. Read you instructions to determine what propeller is recommended for your application. E.G., 10x6. Then for break-in choose a propeller that has the same pitch, but one inch (25.4mm) less diameter, i.e., 9x6. This will allow you to reach peak operating RPM without running the engine hard and lean.
Make sure you have good fuel. See our FAQ on fuel. Use the fuel you intend to fly with. It never hurts to add about 4-6 oz. of oil to a gallon for the first few tanks. Either castor or synthetic is fine. Make sure you have a good tank installation. Any air in the fuel line during running can cause major problems. Even on a test stand you have to be careful - wrap your tank in foam, keep it clean and free of leaks.
Open the high-speed needle about two more turns than factory setting. If you have moved the needle valve, then this is about 5 turns from closed. Six for the 120. Do not touch the low speed needle. (see our tech sheet on setting an R/C carb) Start the engine at full or part throttle, but not at idle. As quickly as possible, move behind the engine (never stand in front of a running engine - see the safety instructions) and advance the throttle to full.
The engine should be rich. Leave the battery on the glow plug for a while and let the engine run. After about one minute you my start to lean in the high speed needle and remove the glow plug battery. (I use a piece of tubing with a hole in the end as a remote needle so I don’t have to get my hand near the propeller - see the safety instructions) The instructions and engine specifications will tell you what the normal engine RPM is for your engine. This is where you should run it. For example, if your engine normally should turn a 10x6 APC at 17000, then you will run the engine during break-in at 17000 on a 9x6 propeller --- RICH. If the engine will not reach this rpm rich, then something is wrong and you should immediately stop and read the instructions, or call us.
The object is to run the engine for at least 30 minutes rich, and at its proper RPM before it goes into the airplane. This will give you a chance to check out the throttle characteristics and get used to the engine. After the 30-min. test, then switch to your flying propeller and see if it operates properly. It is much easier to trouble shoot your engine on a test stand, than out at the flying field installed in your airplane—with everybody watching!!!
