Some Thoughts on Bench Running A New Engine
by Jerry Kelly
Safety: The worst injuries I have seen with model engines involved bench running. Make sure that the bench is sturdy, the mount cannot come loose, and the floor area is clear (so you can run if something starts to come loose). This will sound silly, but do not grab for the motor if it starts to move or fall. It is unlikely that the motor could hurt itself if it came off the mount.
Propeller: Use a propeller that is a little smaller than the prop that you intend to use while flying. For instance – – how about an 11/6 or 10/6 on a .60 or a 9/6 on a .35 or .45? This is O.K. – – the smaller prop will let the engine run in the normal RPM range of the engine while it is still slightly rich. Don’t worry about the smaller prop letting the engine run at too high an RPM: if the engine comes apart blame the engine, not the prop.
Carburetor: If your engine has a R/C carb you should arrange a method of keeping the carb set for maximum speed or, said another way, wide open. I do not mean the needle valve, but the barrel of the carb which is controlled by the servo when installed in the airplane. Continued running of a new engine at other than this setting can cause a build up of varnish that can do permanent harm to the engine. On some engines, the main needle valve will not effect the mixture unless he carb is wide open. So make sure that the carburetor is open.
Start the Motor: Wear ear protectors or put some cotton in your ears and take the motor some place where it will not disturb anybody and crank it up. Now, some people have a knack for starting motors and others don’t , but if you don’t have it going within five or ten minutes stop, re-read the instructions, check the plug, battery, leads, tank, tubing and tighten the prop. If it is flooded, disconnect the fuel line and flip the engine backwards. DO NOT keep flipping it for hours and then complain. It’s a 100 to 1 bet that you are doing something wrong, so get some help if you can’t find the trouble yourself.
It’s Running: Screw the needle valve in so that the engine is running near its peak power. Then immediately unscrew the needle valve until there is a good loss of speed and you can see a cloud of exhaust coming from the engine. Disconnect the glow plug and run the engine like this for about ten minutes.
Second Stage: get safely behind the engine on the side opposite the exhaust and squeeze the fuel tubing until the motor revs up and release the tubing immediately. If you hang on it will kill the motor, so restart and continue this pinch-release method until you have run the motor another 10 minutes.
Enter Third Stage: for the next ten minutes try to run the motor at high RPM by squeezing the fuel line evenly for about five or ten seconds, then releasing for four or five seconds and letting it cool off. Repeat this until the 10 minutes are up.
Final Check: Lean the motor out using the needle valve so that the motor is running about 500 RPMs under the maximum and see if it will run through a whole fuel tank without leaning out dangerously. If it won’t, repeat the third stage until it will.