General Description

Section II - General Description

1.  General

The engine is a static, seven cylinder, radial, air-cooled four cycle engine with a piston displacement of 499 cubic inches.  The cylinder bore is 4.625 inches and the stroke is 4.250 inches.

2.  Cylinders

a. Construction and General Features

1.  The cylinders are built up by shrinking cast aluminum alloy heads on forged chrome-molybdenum steel barrels.  The heads are secured to the barrel by means of staked nuts and should under no circumstances be removed except by Warner Aircraft at the factory.  A copper washer is installed between the cylinder head and barrel.

2.  Each cylinder head is provided with one inlet and one exhaust valve.  The inlet valve seats on an aluminum bronze valve seat insert.  The exhaust valve seat is Austenetic steel.  Both of these valve seat inserts are shrunk into the head.

b. Principal Details of Parts

1.  Cylinder Head.  The exhaust port boss faces toward the side of the cylinder head and is provided with two studs for securing the exhaust stacks.  The intake port boss is on the opposite side of the cylinder head.  A gasket is used between the intake pipe flange and cylinder head.  The valve guides and valve seat inserts are shrunk into the head.  Bronze spark plug inserts are screwed and pinned in the front and rear of each cylinder head.  The two integrally cast rocker boxes are each provided with a rivet and each end to hold the quick-adjustable spring fastener on the rocker box cover in place.

2.  Cylinder Barrel.  The cylinder with integral cooling fins, bolting flange, and flange to secure the head is machined from an alloy steel forging.

3.  Valves.  The valves are inclined to the center line of the cylinder at an angle of 32 degrees, permitting an hemispherical combustion chamber.  The exhaust valves are austenetic steel which permits the use of ethylized fuels.  The intake valves are made of low tungsten steel.  The valves have solid stems.  The valves face the air stream for better cooling of the valve seats.  The valves have a face angle of 45 degrees.

4.  Valve Seat Inserts.  The intake valve seat insert is machined from extruded aluminum bronze alloy.  The exhaust valve seat insert is made of austenetic steel.  Both valve seat inserts are faced at an angle of 45 degrees.

3.  Valve Operating Mechanism

a. Construction and General Features

1.  The cam, cam drive gear, and cam follower guides are located in the rear section of the crankcase.

2.  The push rods and push rod tubes are located behind the cylinders.

3.  Push rods, rocker arm bearings, rocker arms, and valve springs are totally enclosed.

4.  The push rods and cam followers are lubricated automatically by oil spray from the crankcase.  The rocker arm bearings and push rod sockets are lubricated by means of alemite fittings on the end of the rocker arm shaft.

b. Principal Details of Parts

1.  The operation of the valves is accomplished through a cam ring which is located in the crankcase rear section, and consists of a hardened alloy steel ring with two sets of four cam lobes each on its outside diameter.  The cam rotates at 1/8 crankshaft speed and in the same direction as the crankshaft.  The cam is supported on a floating type bronze bushing which serves as a bearing surface between the cam ring and the outer surface of the rear main ball bearing cage.  The driving gear is integral with the cam ring, and is driven from the auxiliary shaft by means of a simple spur gear train through an idler shaft.

2.  Cam followers take their bearing in aluminum cam follower guides which are chill cast in permanent mold.  The cam follower guides are supported in reamed bosses throughout their entire length, positively preventing all side motion.  The cam followers make contact with the cam by means of rollers, and have at the opposite end a spherical socket for the push rod.

3.  The push rods are made from steel tubing with hardened and polished ball ends pressed on each end.  The upper ball end fits into an adjustable socket in the rear of the rocker arm.

4.  The rocker arms are supported by replaceable ball bearings.  The rocker arms are made from alloy steel forgings.  The adjustable rocker arm socket is located on the push rod end of the rocker arm while the roller which contacts the valve stem is located on the other end.

5.  Both intake and exhaust valves employ an inner and an outer valve spring.  The springs have dampener coils which face the seat and both springs are wound in the same direction in order to induce rotation to equalize the wear.

4.  Crankshaft

a. Construction and General Features

1.  The single throw crankshaft is made in one piece from an alloy steel drop forging, carefully heat-treated for the highest physical properties, and finish-machined all over to close tolerances.  The crankpin is ground and lapped to exact dimensions.  Counterweights are straddle-mounted to the crank cheeks and bolted to them by steel bolts set in reamed holes, thus providing utmost safety in absorbing torque reactions and centrifugal force.

2.  The crankshaft is bored throughout for lightness and oil passages.

3.  The rear end of the crankshaft is connected with the accessory drive shaft by means of a tongued coupling.  This accessory drive shaft drives the magnetos, the oil pump, and the cam gear; and it also has splines on the end as provision for installing a starter and generator combination drive assembly.

b. Principal Details of Parts

1.  The crankshaft is supported in the crankcase by three ball bearings.  There are two main ball bearings and one thrust ball bearing.  The front main ball bearing is directly forward of the front crank cheek while the rear main ball bearing is directly behind the rear crank cheek.  The thrust bearing is forward of the front main bearing and is separated from it by a bearing spacer.

2.  The front main and rear main bearings are chamfered on the inner races to clear the generous fillets on the crankshaft.

5.  Connecting Rods

a. Construction and General Features

1.  The master and link rods are machined all over from alloy steel forgings, heat-treated for high strength.

2.  The connecting rod assembly consists of one master rod and six link rods which are assembled to the master rod by means of wrist pins locked to the link rods and take their bearing in bronze bushings, which are pressed into the master rod after drilling to provide full force feed lubrication.  Bronze bushings are also pressed into the piston end of all rods for the floating type of piston pins.

b. Principal Details of Parts

1.  The master rod is of a split type, for bolt design, which a replaceable cadmium silver steel-backed bearing shell at the crankpin end.

2.  The wrist pins are made of alloy steel with a very hard ground surface on the outside diameter.  A flat is machined at the mid-point of the wrist pin to provide a recess for the bolt in the link rod which secures the wrist pin.

6.  Pistons and Piston Pins

a. Construction and General Features

1.  The pistons are made from heat-treated aluminum castings, and are so designed as to combine lightness with greatest strength.

2.  The piston pins are made from heat-treated alloy steel with a very hard surface.  They are ground smooth inside and the external surface is lapped to secure a smooth finish.

b. Principal Details of Parts

1.  The earlier engines were equipped with three-ring pistons employing two compression rings and one combination oil control ring.  All of the rings are located above the piston pin bore.

Later engines are equipped with four-ring pistons employing two compression rings and two oil control rings.  The two compression and one oil control ring are located above the piston pin bore while the other oil control ring is located below the piston pin bore on the skirt.

2.  Aluminum alloy plugs are pressed in each end of the floating type piston pin in order to prevent scoring or scuffing of the cylinder walls.

7.  Crankcase

a. Construction and General Features

1.  The crankcase is made up of two heavily ribbed halves which are machined from heat-treated aluminum alloy castings.  The front and rear halves are joined together on one locating stud and six bolts and machined as an assembly and neither the front nor the rear section can be replaced separately for this reason.  This type construction facilitates the assembling of the crankshaft and connecting rod assembly as a unit.

b. Principal Details of Parts

1.  Each section carries one main bearing.  The front section, in addition, supports the thrust bearing.  The crankcase houses the crankshaft, the cam ring, the front part of the accessory drive shaft, the front and rear main bearing sleeves, and the thrust bearing sleeve.  The cam follower guides are held in reamed bosses in the rear section of the crankcase by means of forked crabs.

2.  When specified for use with a pusher propeller, a push type thrust bearing sleeve may be installed in the crankcase as special equipment when the engine is being assembled at the factory.

3.  The cylinders are secured to the crankcase by 5/16" studs which are drive into the cylinder mounting pads on the crankcase.

8.  Induction System

a. Construction and General Features

1.  The induction housing is machined from a heat-treated aluminum alloy casting.

2.  The induction housing consists of a correctly proportioned annular passage in the aluminum casting which also serves to support the engine in the airplane.

3.  The induction housing contains bronze bushings for the geared drive shafts which are lubricated through tubes integrally cast in the housing.

b. Principal Details of Parts

1.  The carburetor is attached to the lower part of the annular ring of the induction housing, and separate intake pipes lead to each cylinder.

2.  The induction housing is so designed as to bring the carburetor and carburetor heat control valve within the overall diameter.

9.  Gearcase and Oil Screen Assembly

a. Construction and General Features

1.  The gearcase is machined from a heat-treated aluminum casting.

2.  The gearcase is attached to the induction housing by means of studs.

b. Principal Details of Parts

1.  The oil pump is mounted in an accurately machined recess in the gearcase.

2.  The magnetos are mounted on brackets attached to the gearcase.

3.  The construction is so arranged as to allow the mounting of a starter between the two magnetos.

4.  The oil screen and by-pass valve assemblies are mounted in a machined recess in the lower part of the gearcase housing.

10.  Lubrication System

a. Construction and General Features

1.  The oil sump housing is machined from a heat-treated sand cast aluminum casting.

2.  The oil tube elbows are cast bronze.

3.  The oil pump housing assembly is composed of three parts which are machined from heat-treated aluminum castings.

b. Principal Details of Parts

1.  The oil pump fits into an accurately machined recess in the gearcase at the rear of the engine.  The pump is arranged in tandem with one drive shaft operating both the pressure pump and scavenger pump.

2.  The oil is drawn from the oil tank by the pressure pump and from there it is forced through and oil screen mounted in the gearcase to the accessories drive shaft and thence to the crankshaft.  It passes through drilled passages to the crankpin bearing and from there it is forced into each wrist pin bearing.  The oil which is forced out of these bearings lubricates the remainder of the engine by splash and then collects in the oil sump which is located at the bottom of the crankcase.  The oil is returned from there through the oil tubes, to the oil tank by means of the scavenger pump.

3.  Lubricate the rocker arm shafts using an approved rocker arm lubricant (see Table II for a list of approved rocker arm lubricants).  Care should be exercised not to use an excessive amount of lubricant as the excess grease will accumulate in the rocker arm housing and will flow into the valve guide where it may eventually harden and freeze the valve.

11.  Ignition System

a.  Two Scintilla magnetos are furnished.

b.  Unshielded or radio shielded ignition is optional on the engine.

c.  An impulse coupling can be installed on one magneto when a hand cranking starter is to be used.

d.  A control rod connects the advance and retard levers on the two magnetos.

12.  Carburetor Heat Control Valve

A carburetor air heat control valve attached to the bottom of the carburetor is used to control the temperature of the incoming air.

13.  Accessories

Accessories may be furnished as optional equipment at additional cost.

a.  Starter Equipment

The following starters are available for use on all Super Scarab engines.

1.  Air Injection Starters.  The special compressor unit for these starters attaches directly to the engine on the mounting provided for the starter adapter.  All later cylinder heads are equipped with a boss for installing the injection valves but these bosses are drilled and tapped only if specially requested by the airplane manufacturer when ordering the engine.

2.  Starters are available for all Super Scarab engines.  If using a starter, without generator, a special starter adapter and jaw assembly is required.  If, in addition to the starter, a generator is used, a special generator and starter adapter manufactured by Warner Aircraft Corporation is required to complete the assembly.  This drive is braced by means of a bracket mounted under the oil pump.

14.  Testing of Engine in Plant Before Shipment

a.  Each aircraft engine is subjected to a regular preliminary test and a final test.  The engine must develop full rated horsepower with a test club propeller before it is shipped from the factory.

b.  The tests are conducted with the engine mounted on a rigid test stand.  A two-bladed wood test club which allows the engine to turn approximately at the rated speed of 2050 R.P.M. at full open throttle is installed on the engine for test.  No torque determinations are made during the preliminary or final tests.