How do I break-in my four stroke engine?

Important Before attempting to operate your Magnum XL 80 or 91 RFS, please read through these instructions to familiarize yourself with the controls and other features of the engine. Also, pay careful attention to the Safety Instructions and Warnings in these instructions.

For the more experienced modeler, as you read through these instructions, some of the information may seen elementary and unessential, please understand that the finer details are for the benefit of the modeler who has little to no knowledge of model engines, as well as for the modeler who wants to learn more about the engine.

Notice Read and follow these Safety Instructions and Warnings before attempting to operate this engine!

Safety Instructions and Warnings

The model engine will give you dependable performance and it will be a source of satisfaction and pleasure if you follow these instructions as to its proper and safe use. Do not let pleasure turn into injury and/or tragedy! You alone are responsible for the safe operation of your engine, so act sensibly and with care at all times. This engine is a precision built machine whose power is capable of causing harm to you and others if abused, misused, or if you fail to observe proper safety precautions.

At All Times...

• Keep spectators, especially small children, who can be hurt when the engine is running at least 20 feet away from the operating engine.
• Mount engine properly and securely in the test stand, or on a proper engine mount in the airplane. Follow the mounting recommendations on the airplane's plan and/or instruction manual, or in the test stand manufacturer's instructions. DO NOT clamp this engine into a vise!
• Use the correct size and pitch of propeller for your engine. See the Propeller Specification Chart in these instructions; consult your model's plans and instructions, and always follow the instructions of the propeller manufacturer. NOTE: We recommend using wooden propellers when possible. Nylon and other non-wooden propellers require extra special care and handling.
• Install the propeller with the curved side facing outward. Tighten the propeller nut securely against the washer and the propeller. Use a propeller wrench to tighten or loosen the nut. Do not use pliers!
• Inspect your propeller regularly. If propeller has any nicks, scratches, cracks, or any other sign of wear, discard it! Never alter, repair, bend, or shave a propeller, as this will weaken it.
• Inspect the propeller nut between each run and tighten if necessary. Normal engine vibration can cause loosening.
• To stop engine, adjust throttle linkage to close and cut off air supply. An alternative method to this, is to cut off the fuel supply by pinching the fuel line or disconnecting the fuel line from the carburetor. NEVER us hands, fingers, or any part of your body to stop the propeller. NEVER throw anything into a running engine to stop it!
• Stand behind the engine while performing any adjustments. Keep your face, body, and any objects away from the path of the propeller while starting and running your engine.
• Never lean your face over the engine while you are starting or running the engine.
• If you carry your model while the engine is running, be very cautious. Be aware of the propeller and keep it away from you and all others.
• Do not have tight fitting cowlings or oversized spinners, as they will impede airflow to engine, causing the damage to the engine due to overheating.
• Do not fly your model under of near high tension electrical wires.

Installation

When installing either the XL 80 or 91 RFS, use strong engine mounting beams. Use mounting beams that would support a 2-stroke engine of 15cc or greater displacement. Ensure that these beams are firmly integrated with the airframe, reinforcing the internal surrounding structure as necessary to absorb vibration. Installation should be made in such a way as to allow easy access to basic maintenance of your motor, including the checking and adjustment of valve clearances.

Silencer Assembly

Screw the exhaust header pipe into the exhaust port until it "bottoms out," then, unscrew it to the necessary exhaust outlet angle. Secure the pipe in this position by tightening the locknut firmly against the cylinder head.

Carburetor

The needle valve and throttle lever locations are interchangeable by reversing the carburetor. To reverse the carburetor, do the following:

1. Remove the carburetor by carefully unscrewing the two screws which secure both the carburetor and the choke valve. The carburetor will revolve around. If the carburetor is difficult to remove, loosen the two screws which secure the intake pipe to the cylinder head.
2. After reversing the carburetor, re-fit the carb to the intake pipe gently, being careful not to damage the O-ring in the carburetor.

Choke Valve

The Magnum XL 80 & 91 Ringed Four Stroke Cycle Engines are equipped with a spring loaded choke valve. The choke valve operating lever can be located right or left by reversing the hexagon nut and cap screw.

After mounting the engine in the model, determine the correct length of the L-shaped choke rod. If the supplied rod is too long, reduce it to the required length. If the required rod length is longer than 1 ½", be sure to support the outer end to avoid unnecessary vibration. When necessary length is achieved, secure the L-shaped choke rod by tightening the set screw.

Fuel Tank

The suggested fuel tank size is 320 cc or 12 oz. This will allow approximately 12 minutes of running time of normal operation. Locate the fuel tank so that the center line of the tank is 10 to 15 mm below the center line of the needle valve.

Fuel

The Magnum XL 80 & 91 Ringed Four Stroke Cycle Engines run on standard commercially available model glow plug engine fuel. Because these engines are Ringed, it is especially important to fuel with castor oil, with a recommended 18%. Additionally, a fuel containing 5-15% nitro-methane is recommended.

Glow Plug

A Thunderbolt 4 Cycle Glow Plug is recommended for the Magnum XL 80 & 91 Ringed Four Stroke Cycle Engines. With a 4 stroke engine, ignition of the fuel charge takes place at every 4th stroke of the piston instead of every second stroke. Because of this, some conventional 2 stroke glow plugs will not suit this engine. For general use, the Thunderbolt 4 Cycle Glow Plug is recommended.

IMPORTANT Use well balanced propellers and spinners only. An unbalanced propeller or spinner will cause vibration and loss of power.

Propeller

The choice of propeller depends on the design and weight of the model and on the type of flying demanded. Determine the best size and type after practical experiment. Remember, choose the propeller that will enable the engine to best fly the airplane. As starting points, suggested propellers are:

Note Slightly smaller or larger props than those listed above can be used. However, it should be noted that propeller noise will increase as RPMs are raised. For safety, keep your face and other parts of the body well away from the propeller when starting the engine or adjusting the needle valve while engine is running. Be very careful and realize the size of propeller being used, as these larger sized propellers turn through a wide arc.

WARNING There is always a danger, especially with nylon propellers (and other variables such as engine speed and the weather conditions), of the propeller fracturing and a blade flying off. This could very easily cause a serious injury. Therefore, never bend-over the engine when it is running and keep all onlookers a safe distance behind the model. If a spinner is being used, make sure that the spinner notches are large enough to clear the propeller blades and do not cut into and weaken the blade roots when the propeller nut is tightened. There is also a risk, particularly with 4 stroke engines, of the propeller loosening and flying off if the propeller nut loosens due to detonation or "knocking" when the engine is run too lean or under too heavy a load. This problem is very dangerous. To deter this danger, we have developed the special Propeller Locknut. This prevents the propeller from flying off, even if the propeller itself should slip or loosen.

1. Ream the propeller center hole to 8mm diameter, making sure that the propeller is properly balanced.
2. Fit the propeller to the engine shaft, followed by the retaining washer and propeller nut, and tighten firmly with wrench.
3. Fit the propeller locknut. Tighten the locknut firmly using wrench.

Important Regardless of the type of propeller securing used, always check the tightness of the propeller before starting engine. It is important to remember, especially with wooden propellers that there is a tendency for the propeller material to shrink, or for it to be reduced by the serrated face of the drive hub.

Starting

It is always preferable (for safety reasons) to use a heavy duty electric starter, although hand starting is also possible, and will be explained later.

1. Fit a spinner so that an electric starter can be used.
2. Open the throttle so that the throttle arm is a ¼ of its full throw.
   1. If a silencer pressurized fuel system is employed, set the needle valve 2 to 2 ½ turns open from the fully closed position.
   2. If a silencer pressurized fuel system is not employed, set the needle valve 3 to 4 turns open from the fully closed position.
3. Ignite the glow plug and apply the electric starter (Be sure that your battery starter is in good condition and fully charged) after making sure that the battery leads are properly connected for counter clockwise rotation. If the power of your starter is insufficient to immediately rotate the engine freely, turn the propeller clockwise until compression is felt, then, with the propeller in this position, apply the starter again. This will allow the kinetic energy of the rotating propeller to assist in bringing the engine through the compression stroke.
4. When the engine starts, keep it running by steadily moving the throttle to the fully open position. If the engine slows down because the mixture is excessively rich, close the needle valve slowly until the engine runs smoothly. Once this is achieved, disconnect the battery from the glow plug and close the needle valve slowly so that the RPMs increase. Be careful to adjust the needle valve gradually, as abrupt adjustments of the needle valve may cause engine to stop.

Caution Never apply an electric starter with the choke closed, as this will cause an excess quantity of fuel to be drawn into the cylinder and may result in a hydraulic lock that may damage the engine.

Hand Starting

The Magnum XL 80 & 91 Ringed Four Stroke Cycle Engines can be safely hand started – except when using a lightweight wooden propeller. For safety, always be sure to use a "chicken stick". To hand start your engine, follow the procedures below:

1. The propeller should be fixed in such a way that it is positioned horizontally as compression is first felt when turning the propeller counter clockwise.
2. Adjust the needle valve:
   1. If a silencer pressurized fuel system is employed, set the needle valve 2 to 2 ½ turns open from the fully closed position.
   2. If a silencer pressurized fuel system is not employed, set the needle valve 3 to 4 turns open from the fully closed position.
3. Open the throttle fully. Glow plug ignitor MUST NOT be connected at this time.
4. Prime the engine by closing the choke valve and turning the propeller through 4 - 5 revolutions (depending upon the length of the fuel line) to draw fuel from the tank to carburetor.
5. Reopen the choke valve and close the throttle to its starting setting.
6. Turn the propeller counter clockwise several times to draw fuel/air mixture well into the cylinder.
7. Gradually turn the propeller counter clockwise until compression is felt.
8. Connect the glow plug igniter. Place the chicken stick at the center of the right blade, and swing the propeller clockwise from the set position (where compression is felt). The engine will then bounce in the counter clockwise direction to the point where ignition and expansion of the charge takes place. If the engine stops, make sure that fuel is reaching the carburetor from the fuel tank, then repeat Steps 3 through 7. Remember, correct priming is the key to easy hand starting.
10. When the engine starts, keep it running by steadily moving the throttle to the fully open position. If the engine slows down because the mixture is excessively rich, close the needle valve slowly until the engine runs smoothly. Once this is achieved, disconnect the battery from the glow plug and close the needle valve slowly so that the RPMs increase. Be careful to adjust the needle valve gradually, as abrupt adjustments of the needle valve may cause engine to stop.
11. To restart the engine when it is hot after a run, make sure that the throttle is in the idling position, and that the glow plug is charged, and Flip the propeller. If the engine does not restart, Disconnect the glow plug igniter, and then prime the engine by closing the choke valve while rotating the propeller once or twice until the cylinder becomes cool enough for restarting.

Note It is possible that excess fuel in the carburetor may drip into the engine compartment when the choke valve is reopened. Therefore, it is suggested to drill a drain hole in the bottom of the engine bay or cowling and to apply fuel proof paint to the surrounding surfaces to prevent fuel from penetrating the airframe structure.

Engine Break-in

All internal combustion engines benefit, to some extent, from extra care when they are run for the first few times – known as break in. This is because the working parts of a new engine take a little time to seat after being subjected to high temperatures and stress. However, because Magnum Engines are made with the aid of the finest technology, and from the best and most suitable materials, only a very short and simple running procedure is required and can be completed with the engine installed in the model.

To complete the break in, use the same sized propeller to be used to fly your model, and follow the instructions below:

1. Start the engine and run it for about 5 seconds at around maximum RPM, then open the needle valve ½ turn to produce a rich mixture for cooler, slower running. Run the engine for 20 seconds at this setting.
2. Keep the throttle fully open, using only the needle valve to reduce the speed.
3. Repeat Steps 1 & 2, alternately running the engine fast and slow with the needle valve, while gradually lengthening the time of the maximum speed running until 2 full tanks of fuel are used up.

Note Take care to avoid dirty, dusty, and sandy locations to prevent foreign matter to be drawn into the engine, and seriously damaging its working parts.

After completing the initial break in on the ground, the engine should be given a period of moderately rich running in the air. For the first flights, set the needle valve rich, consistent with adequate take-off power and steady level flight. If necessary, readjust the throttle trim on the transmitter so that the engine does not stop when the throttle is fully closed.

With each successive flight, close the needle valve slightly, until, at the end of 10 flights, the needle valve is set for maximum power. It is now time to adjust the carburetor for optimum throttle performance. See Adjusting the Carburetor Section below:

Note While the engine is being broken in and the needle valve has been set on the rich side, the carburetor cannot be expected to show its best response. Therefore, avoid abrupt throttle operation at this stage.

Adjusting the Carburetor

The carburetor of your Magnum 4 Stroke Engine has been factory set for the approximate best results, but the settings may vary. If the desired throttle response is not obtained after the completion of the break in period, the carburetor should be adjusted as follows.

• Needle Valve: Used to adjust the mixture strength when the throttle is fully open.
• Mixture Control Screw: For adjusting the mixture strength at part throttle and idling speeds. Allows engine to obtain steady idling and smooth acceleration to medium speeds.
• Throttle Stop Screw: For establishing the minimum idling speed.

Note All final adjustments to the carburetor must be made with the glow plug lead disconnected.

1. Set the throttle lever ¼ open from the fully closed position and start the engine in the usual way. It is favorable to have the throttle only slightly open, to avoid needless high revolutions when the engine is started.
2. Open the throttle fully and gradually close the needle valve until the engine is running at its optimum RPM in the air. To achieve this, if your engine is installed in the airplane, hold the airplane nose up and then adjust engine for maximum RPM on the ground. Then "richen" until a definite audible RPM drop is heard. As 4 Stroke Engines may be difficult to hear an audible drop, a tachometer may be helpful. Normally, this would occur at 1/8-1/4 turn. This adjustment will be the maximum RPM in the air.
   
   Note Make sure that the engine is fully "broken in" before operating it continuously at full power. (See Break in section)
3. After setting the needle valve as described in 1 & 2, close the throttle and run the engine at idling speed for about 5 seconds, then steadily move the throttle to the fully open position by means of the throttle servo.
   1. If, at this point, the engine hesitates before gaining RPM, with a low pitched exhaust note and an excess of exhaust smoke, it is probable that the idling mixture is too rich. In the scenario, turn the mixture control screw clockwise about 45 degrees.
   2. If, on the other hand, the engine hesitates or even appears to cease firing for an instant before increasing RPM, it is probable that the idling mixture is too lean. In this case, turn the mixture control screw counter clockwise about 90 degrees, then turn it clockwise 45 degrees.
   3. Begin Step 3 again.
   
   
   Caution: For safety considerations, it is advisable to top the engine while changing the mixture control screw settings. Turn the mixture control screw 30 - 45 degrees at a time in the early stages. When the response improves, turn the mixture control screw 10 - 15 degrees at a time. Make adjustments gradually and patiently, being conscious of the symptoms of rich and lean running, explained above, until the engine performs quickly and positively to the throttle.
4. The throttle stop screw is for adjusting the minimum idling speed. If, after adjusting the mixture, the idling speed is found to be too high, the throttle stop screw should be turned counter clockwise until the desired idling speed is obtained.
   
   Note Once the correct carburetor settings have been set, it should be unnecessary to make changes. Slight needle valve readjustments as may be required to counter variations in weather or other conditions will not normally affect the other 2 controls. Minor adjustments may be necessary for top performance if different types of fuel, glow plugs or propellers are used. In these cases, begin flying the model with the needle valve about 1/8-1/4 turn from maximum RPM as a safety measure, then adjust as necessary to gain top performance, remembering that the engine will always lean out in the air, increasing the performance.

Carburetor Cleanliness

1. It is very important to ensure that the fuel entering your engine is clean. For this reason, it is suggested to install a filter between your fueling container and the tank. Additionally, it is also recommended that an in-line filter be installed between the tank and the carburetor.
2. If you have chosen to install these filters, be sure to clean the filters to remove the collected dirt and other foreign matter. Finally, it is suggested to occasionally remove the needle valve holder from the carburetor, and extract any matter lodged in this area.

Valve Clearance Adjustment

Valve clearances are correctly set before any Magnum Four Stroke Engine leaves the factory and, in normal use, will seldom require adjustment. However, if after a considerable amount of running time has been accumulated, a loss of power is detected, or if the engine has been disassembled or repaired due to a crash, valve clearances should be checked and adjusted as necessary. Valve clearances must be checked and re-set only when the engine is cold! For checking and adjusting the valve clearances:

1. Remove the rocker cover by unscrewing the two allen screws from the rocker box on top of the cylinder head.
2. Turn the propeller until compression is felt, then turn it ¼ turn and stop. Both valves should now be closed.
3. The required valve clearance is between 0.04 mm and 0.10 mm, measured between the valve stem and the rocker arm. Use a 0.04 mm and 0.10 feeler gauges to check clearance. The 0.04mm feeler should pass through the gap, while the 0.10 mm feeler should not.
4. If the gap is found to be less than 0.04mm or more than 0.10mm, carefully slacken the locknut on the rocker arm with a 5mm wrench, and turn adjusting screw with screw driver to open or close the gap, then retighten locknut.
5. Check gap again and adjust if necessary.

NOTE Incorrect valve clearances may cause difficult starting (due to valve not closing properly) or loss of power (due to valve not opening sufficiently).

Needle Valve Extension

The supplied needle valve with this engine is designed to incorporate an extension so that, when the engine is enclosed within the fuselage, the needle valve may be adjusted from the outside. An L-shaped rod, of 1.6 - 1.8 mm in diameter, and of necessary length for intended purpose, should be inserted into the needle's center hole and secured by tightening the set screw in the needle valve knob with the included small allen wrench.

Care and Maintenance

To ensure that you obtain long life and peak performance from your engine, observe the following:

• Avoid running the engine under dusty conditions. If necessary, play a sheet of plywood in front and under the nose of the model when starting your engine.
• Dirt and other matter in the fuel may cause the carburetor jet to become clogged. To prevent this:
  • Before installing fuel tank, rinse with methanol or fuel.
  • Install a fuel filter in the fuel tubing between carburetor and fuel tank.
  • Install a fuel filter between the fuel tank and the fuel pump.
  • Clean filters periodically.
  • Do not leave your fuel container open needlessly.
• Do not leave raw fuel in the engine at the conclusion of a flying session as it may cause corrosion. It is important to drain the fuel from the engine after a flying session. One method is to disconnect the fuel tubing from the carburetor while the engine is running and allow the engine to burn all remaining fuel. Additionally, pump all fuel from tank.
• Once engine has run dry, add After-Run Oil into the crankcase via the glow plug hole, into the crankcase breather hole, and into the carburetor. Once the oil has been added, rotate the crankshaft to distribute the oil to the bearings, etc. Failure to properly lubricate the engine with an after run oil may cause internal rusting, resulting in engine malfunction and voiding the warranty.
• Clean the exterior of the engine with a clean cotton cloth, removing oil and dirt from the crankcase. If this is not done, oil and dirt will burn into the outside of the engine every time it is run and eventually the crankcase will become blackened.
• If the engine is not to be used for an extended time, more than 45 days, remove the glow plug and rinse out the interior with kerosene, (not gasoline) and rotate the crankshaft. Shake out any residual kerosene, then complete Step 4 to properly lubricate the engine with after-run oil. Additionally, it is recommended to remove the valve cover and lubricate the pushrods, rockers, and valve stems. Replace valve cover.
• Do not take engine apart as this will void all warranty.

First Flight Tips

When your plane is in the air, the environment changes slightly for the engine. The propeller load is reduced and air blows faster over the carburetor. When the airplane dives, the opposite happens. The final adjustment of the needle valve is a matter of trial and error. Start your engine and hold the aircraft with the nose up about a 45 degree angle. Then enrichen the fuel (open valve) until there a noticeable drop in RPM. Try a flight at this position. If you see a light vapor trail from the aircraft, you have attained the optimum setting, allowing for great performance and proper engine cooling. If the engine does not run smoothly or stops during a dive, the needle valve may be too rich. If the engine runs smoothly at full power but flames out during acceleration, you may have to make the idle mixture slightly richer. A series of short flights should be enough to get the proper setting. Remember, it is always better to err on the rich side.

Frequently Asked Questions