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Section IV - Installation Of Engine In Airplane

1. General

a. Engine Mount

1. Before the engine is mounted in the airplane, great care must be taken to inspect the bosses on the mounting ring for flatness. They must be flat within .003 inches if the engine is bolted up solidly, whereas a maximum variation of .015 inches is permissible if wood veneer or suitable auto brake linking, approximately 1/8" thick, is used between engine and the mount.

2. Rubber mounts of proper design and manufacture, which allow no fore and aft motion at each mounting bolt and only a very limited flexibility to absorb the torque impulses in the radial direction may be considered satisfactory. Rubber motor mounts with excessive radial flexibility or giving any appreciable fore and aft motion must not be used as excessive stresses will be imposed on all engine parts from inertia and gyroscopic loads.

3. In installations where rubber bushings are provided at each mounting bolt to eliminate telegraphing of vibration to fuselage structure, great care must be taken at the periodic inspection that these bolts have not become loose. These bushings are provided to eliminate the telegraphing or noises rather than to allow appreciable movement of the engine. All bolts must be equal in tension and as tight as possible without placing undue strain on the bolts.

4. If in doubt as to the mounting, we suggest you communicate with us and we shall be glad to forward service instructions.

5. Regular 5/6" Aircraft bolts must be used for the installation of the engine to the airplane.

b.  Fuel Supply

1. The fuel line should be made of 3/8" O.D. tubing. All fuel lines should be made of seamless copper tubing which has been heated and quenched after bending.

2. A fuel strainer must be installed in the fuel line.

3. A 1/4" or 3/8" Briggs Standard pipe tap was used on early carburetors but the carburetors which are now installed on these engines will have a 1/2" Briggs standard pipe tap at the fuel inlet.

4. A 1/8" Briggs standard pipe tap is provided on the upper side of the top mounting lug for the installation of a primer.

c. Lubrication System

1. Oil Tank

(a) The oil tank should have a total capacity of approximately six gallons. In service it should be filled with five gallons of oil which allows an air space of approximately 20% of the capacity which is sufficient for the expansion of the oil. The oil tank should be located near the engine so that its lowest point is slightly above the oil pump when this airplane is standing on the ground.

(b) The oil lines between the engine and the tank should be 3/4" O.D. seamless copper tubing which has been annealed and quenched after bending to remove all stresses.

(c) A 5/8-18 tapped hole should be provided in the oil tank wall close to the bottom, or in the oil line from the tank to the engine for the oil thermometer. When placed in the oil line, the thermometer well should be made to Air Corps drawing S31B1096 as shown in volume 1 of "Handbook of Instructions for Airplane Designers". The oil thermometers used should have a range of 0 to 200 F. (or 18 to 93C.)

(d) The drain plug in the oil tank and the oil outlet from the thank must be placed at the lowest point of the tank.

(e) The filler cap should be about 2 inches in diameter and provided with a vent.

(f) When the airplane is stunted frequently, a 3/8" O.D. vent tube should lead from the top of the tank to the 1/4" pipe tapped hole provided for this in the rear wall of the induction housing.

2. Oil Pressure Gauge and Fittings

(a) The oil pressure gauge connection fits into a 1/8" Briggs standard pipe tapped hole on the top of the gearcase.

(b) The oil pressure gauge line is made from 1/4" O.D. copper tubing.


During cold weather, the engine oil in the oil gauge line may become so viscous that it would cause the oil pressure gauge to work sluggishly. Normal operation may be secured by disconnecting the line, blowing it out with air, refilling with petroleum base hydraulic brake fluid, and then reconnecting the line. Ordinarily, this treatment will suffice for a period of 60 to 90 days, after which time it can be repeated.

(c) An elbow fitting must be used at the gearcase in order to clear the tachometer shaft. All engines equipped with a generator drive adapter installed at the factory are furnished with this elbow and a right angle tachometer drive in place, as they must be installed before the generator drive adapter is mounted to the engine.

(d) The oil pressure gauge should have a range from 0 to 150 pounds per square inch.

d. Ignition System

1. Both battery and magneto ignition are available on the Super Scarab and Scarab engines.

2. Care must be taken to install the proper switch for the different ignition systems used. A switch closing the circuit is required for cutting off magneto ignition by means of grounding, whereas a switch opening the circuit is required for cutting off battery ignition.

e. Cowling

1. Two 5/16-24 tapped holes are provided on the front side of each rocker arm housing, for attaching the cowling to the engine.

2. If an additional attaching point is desired, and no air starter is used, the air starter boss on the cylinder head can be furnished taped 5/16-24 upon special request, and a bracket may be used.


At no time should the cowling rest upon the springs of the rocker arm housing cover.

3. On all installations equipped with N.A.C.A. cowlings, a cylinder head temperature indicator must be installed to take a reading at the rear spark plug for test purposes.

4. When cylinder head temperature indicators and thermo-couples are installed, care must be taken that the thermo-couple under the spark plug is fitted tightly against the bronze spark plug insert. There must be no distortion of the thermo-couple gasket which will allow possible leakage.

5. An Army-Navy type thermo-couple gasket should be used and the tab should be placed in the recess provided at No. 1 cylinder rear spark plug boss. If the recess is not provided one should be carefully chiseled for the tab to lay flat to prevent distortion of the gasket and possible leakage. Leakage at this point will cause erroneous readings.

f. Exhaust Manifolds

1. Exhaust manifolds should be so designed that there will be no more than eight inches of water back pressure.

2. Exhaust manifolds should have flexible joints between the exhaust ring and exhaust pipes leading from the exhaust ports into the collector ring.

g. Propeller Mounting

1. The propeller should be designed and set to allow the engine to turn up at least the rated speed in full throttle level flight. The advantages of the proper propeller installation are:  best all-around performance of the plane, best fuel economy, and the minimum amount of stress upon the engine.

2. Quite often a very pronounced roughness will be experienced even with new propellers, due to a static or dynamic unbalance or due to differences in the shape of the two blades. It will be found that roughness will be most pronounced at certain speeds due to the fact that at these speeds there is a synchronization between the impulses and the natural period of the structure. All engines are very carefully and uniformly balanced before passing inspection in the factory, and if roughness is experienced in the airplane it is advisable to determine the origin of the roughness and to change propellers before trying to remedy it by making adjustments on the engine.

3. Another source of roughness may be due to a loose fit between the propeller hub and the crankshaft.

4. For proper operation, a propeller should track within 1/16" at the tip, and when an adjustable propeller is used, the adjustment between the two blades must be alike within 1/4. All surfaces and edges of the propeller blades must be smooth and any pitting should be smoothed down with a fine file and emery cloth, and finished with crocus cloth. The propeller must be rebalanced if an appreciable amount of material has been removed. In this connection, it is well to remember that removing only 1/4 ounce from the tip of one blade of a 7-1/2' propeller results in an unbalanced radial force of 84 pounds at 2050 R.P.M.

2. Installation of Engine In Airplane

a. General

1. Since the installation and removal of Super Scarab engines varies in different airplane models, the following outline may serve as a general guide for the typical job.

2. At least two men are required for this operation, and procedure will follow the steps indicated below, with variations permitted when the particular installation so requires.

3. Improper use of the engine hoisting equipment may result in serious damage to the engine. The hoisting equipment must be attached to the engine lifting eyes only. The equipment must not be used for lifting an airplane or the engine when it is attached to the engine mount.

b. Attaching Engine To the Airplane Mounting Ring

1. Attach lifting sling to the engine lifting eyes, take weight of engine on hoist, and remove bolts holding engine to assembly stand.

2. Raise the engine to the level of the airplane mounting ring.

3. Carefully guide the rear section of the engine through the mounting ring being careful to avoid striking any part or the engine or its projecting parts.

4. Install, tighten, and safety main engine mounting bolts. Remove engine sling and hoist.


Do not install mounting bolts without a flat steel washer between the bolt heads and the aluminum induction housing mounting bosses. Draw up evenly on all bolts to assure proper alignment of the engine and mounting ring.

c. Connecting Controls and Installing Accessories

1. Connect battery ground wires.

2. Connect oil pressure gauge lines to oil pressure gauge connection on gearcase housing.

3. Attach tachometer cable to tachometer drive.

4. Connect oil tank overflow to the induction housing.

5. Connect both magneto ground wires.

6. Install thermometer bulb in the oil inlet line.

7. Install generator and starter, if provided, making all electrical connections necessary.

8. Connect the control rod to the advance-retard lever on the rear of the magnetos, and test for full action in both directions when operated from pilot's cockpit.

9. Connect mixture and throttle controls to carburetor and test the controls to ascertain minimum and maximum operation of control levers when operated from the pilot's cockpit.

10. Install gasoline supply line to the carburetor.

11. Connect the carburetor air scoop, and the heat control valve to carburetor control, if the airplane is so equipped.

12. Connect "Oil in" and "Oil out" lines to oil pump.

13. Install exhaust stacks or exhaust collector ring.

14. Carefully inspect all installation connections and their safetying. Any loose electrical wires, tachometer cables, or lines of any kind must be securely taped down to prevent chafing or breaking during service.

15. Install necessary cowling.

d. Installing Propeller

1. General

(a) Before installing a propeller or hub, all parts will be examined for defects and damage, and checked for proper fitting.

(b) All raised portions of nicks, burrs, galls, scores, etc. on joining surfaces will be carefully dressed off and thoroughly cleaned before the propeller or hub is assembled on the crankshaft. All external surfaces, except the thread portion of the hub of the hub retaining nut, the rear cone, and the rear cone seat (which is to be installed dry) will be coated with clean engine oil to provide lubrication and prevent corrosion.

2. Installation On Splined Shaft

(a) In the order given, assemble the rear cone spacer (if used), rear cone, propeller hub, front cone, and propeller hub retaining nut on the crankshaft.

(b) Screw in retaining nut.

(c) Install snap ring.

(d) Secure the retaining nut by installing and securing the clevis pin. A washer will be placed under the cotter pin on all propeller hub nuts having elongated locking pin holes.

3. Installation On Tapered Crankshaft

(a) Dress off all raised portions of nicks, galls, scores, etc. on the tapered surfaces, and thoroughly clean the shaft and hub.

(b) Cover the crankshaft taper with a thin coat of Prussian blue. Press hub on crankshaft as tightly as possible without turning it. Then rotate hub about 45 degrees. Remove the hub and examine its tapered surfaces as well as that on the crankshaft. If the parts have the required bearing contact and clearance, the bearing surface at the large end of the hub taper will be evenly coated with a thin film of blue transferred from the crankshaft and the small end will have little or none. Furthermore, the blue on the crankshaft will be light on the hub bearing section at the large end and dark on the small end section where the clearance is required. After completing the check, thoroughly remove the blue from all parts.

(c) If improper fit is indicated, the taper may be trued up by lapping.

(d) When the parts are properly fitted, cleaned, and lubricated, installation is accomplished as follows: Press the hub onto the crankshaft end by hand and, in the order given, screw in and firmly tighten the retaining nut and lock nuts. Use the proper wrenches with no additional leverage. Secure the lock nut with the lock ring.

(e) Before starting engine, all oil, moisture, or fuel accumulated should be drawn from the cylinders as outlined in the section on storage of engines.


Specific operating instructions and preflight instructions outlined in other sections of this publication must be complied with before engine is placed in service.

3. Removing Engine From Airplane

a. The removal of the engine approximately reverses the procedure outlined in the preceding paragraphs. As the removal of the engines may vary slightly in different airplanes, the following guide may serve as a general guide for the typical job. This operation requires two men, and whenever possible should be accomplished indoors where a suitable hoist, parts bench, and other necessary facilities are available.

b. Removal of Propeller

1. Removal From Splined Crankshafts

(a) Remove the clevis pin securing the propeller hub retaining nut.

(b) Unscrew the propeller hub retaining nut. This should draw off the propeller hub.

(c) If the above fails, then additional force must be used. First remove the snap ring, nut and cone. Then thoroughly clean the threaded portions of the nut and shaft. Lubricate the cone, nut, and shaft with clean engine oil, reassemble and apply sufficient force to loosen the hub from the rear cone. Unscrew the propeller hub retaining nut.

2. Removal From Tapered Crankshaft

(a) Remove the safe tying lock wire or cotter pin.

(b) Remove, clean, and thoroughly lubricate the threads of the lock nut and retaining nut.

(c) Thoroughly lubricate the threads of the-hub and crankshaft.

(d) Reinstall and tighten both nuts. Then back out the lock nut one turn and back out the retaining nut until it seats lightly against the lock nut.

(e) Place the proper wrenches on each nut and holding the outer nut stationary turn out the inner nut until the hub loosens from the crankshaft.

(f) After the hub is loosened the nuts and remaining parts can be removed.

(g) If the above method fails to loosen the nub, then additional force must be used. Tap the end of the nut with a soft hammer while force is applied on the nut by the wrench. Two or three applications should loosen the nut after which it may be removed.


Under no circumstances should a flame or any kind be used to heat the propeller hub in an attempt to expand it.

c. Remove cowling as required to permit the disconnecting of all engine attaching controls, lines, and mounting bolts.

d. Drain the oil out of the bottom of the tank by disconnecting the "oil in" connection at the oil sump.

e. Remove exhaust stacks or exhaust collector ring.

f. Removing Accessories and Disconnecting Accessories

(1) Disconnect "oil out" lines to oil pump.

(2) Take off the carburetor air scoop, and the heat control valve to the carburetor control, if the airplane is so equipped.

(3) Disconnect gasoline line from carburetor.

(4) Detach mixture and throttle controls from the carburetor.

(5) Disconnect the control rod from the advance-retard lever on the rear of the magnetos.

(6) Remove generator and starter if installed.

(7) Remove thermometer bulb from the oil inlet line.

(8) Disconnect ground wires from both magnetos.

(9) Remove oil tank overflow line.

(10) Detach tachometer cable from tachometer drive.

(11) Disconnect oil pressure gauge line.

g. Removing Engine

(1) From overhead hoist, attach engine sling to engine lifting eyes that are located on the rear half of the crankcase between the No. 1 and No. 7 cylinders on the left and the No. 1 and No. 2 cylinders on the right. Operate the hoist until the weight of the engine is removed from the airplane but does not lift the airplane.

(2) Remove the engine mounting bolts, leaving the two bolts at the rear or number one cylinder until last.

(3) Slowly separate engine from engine mount, carefully guiding rear or engine past the mounting ring. Lower the engine and attach it to assembly stand with at least four 5/16 inch bolts.

4. Ground Test Prior To Flight

After installation of engine in airplane has been completed and checked, the following steps are necessary for preparing the engine for flight tests:

a. PREPARATION. Remove rocker arm housing covers, and front spark plug substituting plastic plugs. Remove oil screen, wash thoroughly and replace.

b. CLEANING. Thoroughly clean the corrosion preventive compound from the rocker arm housings by spraying the valve stems, springs and housing with mineral spirits. Blow off excess spirits with compressed air and spray valves, valve stems carefully with SAE 40 or 50 lubricating oil, and grease rocker arms while turning the engine crankshaft to work the oil into the valve guides and to inspect for valve sticking. Replace the rocker arm housing covers and install the spark plugs, using thread lubricant.

c. LUBRICATING OIL. Fill the oil tank with proper lubricating oil, the grade of which will be governed by seasonal conditions.

d. TESTING. Start the engine observing that proper oil pressure is maintained. Warm the engine gradually and run at 1000 to 1200 RPM for 15 minutes. A full throttle magneto check should then be conducted to determine proper functioning of the engine. Any malfunctioning of the engine during this test may be caused by spark plug fouling due to the residual corrosion compound in the cylinders. Remove and clean the spark plugs and re-run the magneto check. The amount of corrosion compound in the engine is very small and it will not be necessary to change the oil in the tank at the conclusion of the ground test. It will be necessary to change the oil only at regular oil change periods.

e. INSPECTION. Before the flight test is conducted, inspect the installation very thoroughly to ascertain that no leaks exist in the fuel and oil systems, and that the installation has been properly conducted. Install all cowling and conduct the flight test.

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