Engine Break-In/Installation Tips


The instructions that are supplied with a new engine should be read thoroughly and followed for breaking in and maintaining the engine. If the instructions are not available, these instructions can be used for standard 2 - cycle engines.


Although engine manufacturers have excellent Quality Control systems, there is always a chance that a new engine has small metal filings that can permanently damage an engine if not removed. Prior to being broken in, an engine should be inspected and cleaned to assure that all metal filings and dust are removed. This is done by simply removing the backplate and flushing with new, clean fuel. Any further attempts to disassemble could result in the warranty being voided. At this point, the owner has done as much as can be expected to reduce the chances of damage and any other damage will be covered as a warranty defect.


Modern 2 - cycle engines can produce a surprising amount of thrust. Regardless of whether the engine is mounted on a stand or the model, the mount must be secure so that the engine cannot lurch forward when it is initially started. Disregarding this safety warning can result in serious, permanent injury.


The fuel tank should be located as close to the engine as possible with of the tank level with the carburetor needle valve assembly. The fuel tank system must sealed to eliminate the possibility of fuel or air leakage. If the muffler has a pressure tap, it should be connected to the pressure inlet of the fuel tank. The tank should be mounted on high quality foam rubber to reduce fuel foaming during the break-in operation. Fuel foaming can adversely affect the operation of the engine resulting in improper break-in.


A good quality, commercially available fuel containing between 5% and 10% nitromethane and 20% castor oil is recommended for breaking in a new engine. A fuel with a castor/synthetic lubricant blend may be used but may less effective if the engine should suddenly run lean as the last of the fuel is used. If the oil content is less than 20%, medical grade castor oil can be purchased at a drug store and added to bring the oil level to the appropriate level.


The size of the propeller used for the break-in period is not nearly as important as that used for actual operation. The size chosen should allow the engine to turn at optimum revolutions per minute without stressing the engine or allowing it to overheat. A prop chart recommends a good starting point. Although it might not be the ideal prop, it will be adequate for breaking in the engine.


It is extremely important to check the balance of a propeller before attaching it to an engine. An unbalanced propeller can cause substantial damage to an engine.


The type and quality of glow plug used in the engine varies from one type engine to another. If no plug is recommended, it is best to start with a very high quality R/C long-type plug such as Thunder Tiger, K&B 1L, or O.S. No. 8. Fox plugs have a colder heat range and may work on some of the cooler running engines but can cause frustration in attempting to break-in some of the modern ABC engines. It the engine slows down excessively or dies when the glow plug driver is removed, this might indicate that the heat range of the glow plug is too low.


Most engines produced today do not require a prolonged break-in period. Refer to a prop chart to determine the proper propeller size for break-in. With the propeller installed securely to the engine, the glow plug installed, the fuel lines connected, and the tank filled with fuel, the break-in operations can begin. The idle mixture screw and/or idle stop screw should not be adjusted during the initial break-in period. This will only serve to complicate the process. All adjustments during break-in will be made to the needle valve. The initial setting is made by turning the needle valve clockwise until resistance is felt. This is the fully closed position. Forcing the needle valve beyond this point can damage the carburetor. The needle valve is then turned counter-clockwise about 2 - 2 1/2 turns to open the port to good starting point.

Using the transmitter or throttle pushrod, the throttle is opened to 1/2 to 3/4. Without the glow plug battery connected, a finger is placed over the carburetor opening and the propeller is rotated counter-clockwise 2 - 3 turns or until fuel flows through the fuel line into the carburetor. A 1.5 volt ignition battery or power panel is connected to the glow plug. The throttle opening is then reduced to 1/4 - 1/2 open. The propeller is the flipped counter-clockwise using a "chicken stick" or electric starter. The engine should fire after a few seconds. After the engine starts, leave the glow plug battery connected and advance the throttle to full open. At this point, the engine should be running very rich, i.e. dense smoke and/or heavy oil residue coming from the exhaust.

After the engine runs for a minute or two, the needle valve is closed 1/4 turn clockwise and the glow plug clip is disconnected. The engine should be allowed to consume the entire tank of fuel at this needle setting, making sure the engine remains rich. After the first tank of fuel is depleted, the engine should be allowed to cool for a few minutes. During the second tank of fuel, the engine is run at alternate throttle settings, 1/2 throttle for 30 seconds, full throttle for 30 seconds, and back to 1/2 throttle, until about half the fuel is consumed. At this point, the throttle is slowly advanced to full and the needle valve is closed slowly, about 1/8 turn at a time, until maximum revolutions are reached. Finally, the needle setting is turned about 1/8 turn counter-clockwise to avoid an overly lean running condition and the balance is consumed. The engine is allowed to cool again and the tank is refilled. Without resetting the needle valve, a third tank of fuel is run through the engine while alternating the throttle position ever 30 seconds to 1 minute between 1/4, 1/2, 3/4 and full throttle. At this point, the engine is ready for the first flight. The engine is not broken in completely at this point so care must be taken to avoid running the engine overly lean.