Bentley BR-2 Rotary Engineering Description
The 9 cylinder rotary is an, overhead valve, single row, spark ignition, 4 cycle, engine with a fixed crankshaft and a spinning bank of cylinders. The engine is direct drive and is naturally aspirated.
There is no casting necessary, all parts are made from bar stock !The conservative design has a 5.6 compression ratio and is designed for manufacture with a minimum of specialized equipment. Speed is 400 rpm idle and 2000 rpm at full power. The engine is equipped with an constant loss oil system that supplies pressure lubrication to the crank throw bearing and oil mist lubrication to the front and rear ball bearings. The cam and drive gearing are also mist lubricated. The ignition is equipped with two sets of mechanical automotive points and can be operated with a conventional ignition coil or electronic ignition system.
The crankcase of the engine is made of three sections. The nose section, crankcase section, and the thrust box section.
The nose section is piloted to the crankcase and secured by 14 screws. The nose section houses the cam and associated drive gearing, as well as 18 brass valve tappet bushings for the valve push rods. The propeller hub is piloted to the nose section and secured by 8 screws.
The crankcase, or power section, is machined from 6061 aluminum billet. It is equipped with 9 cylinder mounting faces, each with four tapped holes to receive the cylinder mounting studs. The front and rear faces receive the piloted nose and thrust box sections.
The thrust box is machined from 6061 aluminum billet.
The thrust box houses two ball bearings and a thrust ball bearing to support the engine on the fixed crankshaft. The outer diameter of the thrust box is equipped with 9 intake ports and tapped holes for mounting the cylinder intake fittings.
The rear of the thrust box is enclosed by a cover plate piloted to the thrust box and secured by 36 screws. The inside diameter of the cover is equipped with a sealing " 0 " ring. Inside the cover plate is 18 fins to assure the intake mixture is atomized and delivered to the 9 intake pipes.
The thrust box also provides a mounting diameter for the ignition slip ring.
The cylinder barrels are machined from cast iron, the top end is has a mounting lip and the bottom has two slots to provide clearance for the connecting rod. The cylinder barrels are equipped with a pressed on aluminum cooling sleeve with integrally machined cooling fins. The cylinder heads, cylinders and cooling sleeve are secured to the crankcase by means of four studs.
The cylinder heads are machined from a single piece of 6061 aluminum billet. There are two valve chambers that are integral with the cylinder head and are machined using a special fixture. The exhaust gas exits directly from the cylinder head Provision is made for two ignition spark plugs. The side of the cylinder head is provided with a mounting surface for the intake manifold. Additionally, the cylinder head is provided with a mounting surface for the rocker arms support.
The crankshaft is made from 2 pieces, both are made from 4140 steel.
The rear shaft is mounted and secured in two locations for engine mounting. The rear of the shaft is threaded and secured by two mounting nuts, the remaining thread provides a mount for the air / fuel control valve. The air / fuel mixture is drawn through a hole in the crankshaft to the interior of the crankcase.
The crankshaft reaction torque is secured to the main engine housing by a special nut that draws the shaft into a 7 degree taper. The shaft provides support for the two main ball bearings and the thrust bearing.
The front and rear crank sections are secured by a 5 degree taper and secured by a draw bolt. The front crank shaft is supported by a ball bearing. The bearing is mounted in a plate and secured to the inside of the nose section by 9 screws.A cam drive gear is secured to the shaft by a pin and screw.
The master rod is a single piece machined from 6061 aluminum billet. The lower end is equipped with a plain bronze bushing. The eight articulated or link rods are of the same construction. The master rod is not compensated for the combined motion of the link rods.
The pistons are machined from 2024 aluminum billet. Each piston is fitted with two cast iron compression rings above the piston pin. The piston pin is of the floating type, with aluminum plugs at each end to prevent scoring of the cylinder wall.
The cam, which actuates the valve tappets, is machined from a single ring of 4140 steel, heat treated to 46 Rc hardness for wear resistance. It is supported on the front crankshaft and held in place by three plate mounted buttons. Attached to the cam ring is a purchased spur gear. The cam is driven by means of an intermediate gear shaft and rotates in the opposite direction of the crankshaft at one eighth engine speed.
The valves consists of a single inlet and exhaust poppet valve, machined from 303 stainless steel operating in a brass valve seat. The valves are actuated by means of exposed rocker arms. The valve springs are stainless and secured with a pin and keeper arrangement. The valve train is equipped with solid ball nose tappets, adjustable push rods and pivoted rocker arms. The rocker arms are provided with a roller to actuate the valve stem.
Oil is supplied from an external supply tank through transfer tubes to a positive displacement pump.
The pump is mounted in the main engine housing and is actuated by a cam mounted to the ignition timing drive gear.
The plunger forces the oil past a spring loaded check valve and into a passage in the crankshaft.
The rear portion of the thrust box is equipped with provisions for a fabricated two piece intake fitting. The fuel / air mixture is carried along side the cylinder in a brass tubing and is received by a second fabricated two piece fitting that is attached to the cylinder head. Both the top and bottom fittings are equipped with " O " rings to allow for expansion.
The ignition cam is driven by a set of spur gears with a 2:1 reduction. The engine is equipped with two sets of Ford V-8 ignition points to provide duel ignition through two independent automotive ignition coils. The high voltage from the ignition coils is directed to a duel set of spring loaded brushes. The current is supplied to a ring made from phenoic and equipped with 18 sets of brass contacts. The ring is spinning with the engine. Ignition wires are positively secured to the ring contacts with screws and the wires lead to the cylinder mounted spark plug.