# Bentley BR-2 Rotary Engineering Description



## Reqllmy (2 مايو 2010)

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. ​ 

* Crankcase*

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. 

_* Cylinders*_

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. 

* Crankshaft *

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. ​ 

* Connecting Rods *

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. 

* Pistons  *

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. 

* Cam *​ 

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. 

* Valves *

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. 

* Lubrication System  *

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. 

* Intake System  *

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. 

* Ignition System  *

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.​ 
*Bentley BR-2 Rotary Pictures *​ 





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Bentley BR-2 front view showing the general arrangement of the cylinders, cylinder head tie bolts, intake pipes, valve rocker assemblies, adjustable pushrods and integral propeller hub.​ 






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Rear view showing the intake pipes, nut securing the engine crankshaft taper to the engine frame, support stand, fuel/air control valve and backfire prevention pipes. ​ 







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Rear close-up of cylinders showing the cylinder attachment to the crankcase, Intake pipe attachment to the cylinder head, exhaust passage, rocker arms and support, spark plug location and ignition wire harness. ​ 








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Close-up of the intake and exhaust rocker assemblies, the fabricated intake pipe housing and the cooling fins on the cylinder cuff and head. ​ 







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Close-up of the intake and exhaust rockers, valve springs and keepers and tie rod attachment through the cylinder heads. ​


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## Reqllmy (2 مايو 2010)

Details About the Parts 


*Introduction*

The radial engine plans are the product of more than 70 years of development and refinement. The improvements have come from personally building the engines as well as comments, suggestions and improvements made by other builders. 
This process of improvement continues to this day. The photos and descriptions below are to acquaint the potential builder and enthusiast with the design effort that has gone into these plans. 
This is not a hard engine to build, it is a bit time consuming. Better then watching television ! Many builders have told me this is the first engine they have found that is " A Joy to Build ". 
As I build the engines I am constantly amazed with the subtle thought that went into the original work. 
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*Important Features*

The various views and pictures shown below are from different engines to illustrate important features common to all the engines. 











Front View Rear View 
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*The Crankcase* 





 

The front cover carries the thrust load into the crankcase using a ball bearing. None of the load is carried by the crankshaft main bearings. 
The crankcase is machined from a 5.25 diameter 6061-T6 aluminum round. If you don't have a source for material, see ASAP's web site. ( See the supplier list ). 
The front and rear cover is piloted to the main crankcase to ensure concentricity with the two main bearings. 
The bearing diameter and the pilot diameter are machined during the same setup to ensure concentricity. 
The support rings inside the crankcase are used to pilot the crankshaft main bearings to ensure a rugged assembly. 
The cylinder skirt studs are secured in blind holes to reduce oil leakage. 
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*The Rear Cover* 





 

This is the only casting used in the engine. It is 356-T6 material, heat treated to ensure it will machine beautifully. 
A chucking boss provides easy cleanup of the mounting flange. After the boss is removed, the flange is used to mount the carburetor. 
On the single row engines, the casting supports the carburetor, the distributor assembly and the two oil lines. 
For the double row engines, the casting supports two distributors and the carburetor. 
The shape of the casting and air guide keeps the speed of the fuel/air mixture high and reduces fuel pooling in the lower cylinders. 
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*Main Bearing*





 

The main bearings are 660 bearing bronze. On the front main bearing, the cam runs on a machined lip. 
The rear main bearing supports the oil pump housing and the oil pump shafts as well as the crankshaft. 
Oil from the pressure pump is supplied to the crankshaft at the rear main bearing. 
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*Jack Shaft & Cam Support* 





 

The jack shaft is used to drive the cam at the 8:1 reduction. The gears are purchased from Boston Gear. ( See supplier list ). The jack shaft is piloted into the front main bearing, the other end is mounted in a bronze bushing located on the aluminum cam support base. 
The cam support plate has three nylon pads that hold the cam ring into the front main bearing support ring. 
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*Cam Ring* 





 

The cam is a single steel ring. The intake and exhaust lobes are machined in a single setup. 
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*Cylinder Heads* 







The cylinder heads are the most important part of the engine. They are machined from 6061-T6 aluminum bar stock. The cylinder barrels and the heads are screwed together. A few of the important steps are shown. 
The beginning step in making the cylinder heads is shown. The raw material block is drawn up to the face plate with a bolt. The bolt thread is located between what will eventually become the valve towers. 
At this step. the base of the cylinder head is turned and finned. In the same setup, the inside of the dome is formed and the thread is generated. 
The material is roughed out around the towers. The wedge tool provides the correct angle and the necessary stiffness to turn the towers to the finished diameter and cut the fins using a hook shaped finning tool. 







The drawings for the wedge tool and dimensions for the finning tools are included in the engine plans. 
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_*Cylinder*_

The cylinders are machined from free machining leaded steel. After roughing out the bore, the blanks are mounted on a mandrel. This saves the lathe setup and makes the repetitive finning go faster and more accurately. The support from the tail stock greatly improves the rigidity of the setup. 
Following the finning operation, the thread is machined during a second setup on the mandrel. 
After machining, a hot gun blue finish is used to prevent rusting. A drawing of the mandrel tool is included in the engine plans. 







All of the cylinders, gaskets, rings, valves and rocker arms prior to assembly. Quite a sight, and a signal the engine is well on the way to being complete. 
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*Crankshaft *







To ensure crankshaft straightness, the crank throws are machined as a bolted pair. A 3/8 square broach is used to make the square hole. The part number and source for the broach are included in the plans. 
The square hole takes the torque of the engine, while the 3/0 taper pins hold the various shaft parts together. 
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*Gear Cutting* 







The gears can be purchased. With the higher power of the double row engines, the crankshaft gears can be cut integral to the shaft. 
Part numbers and sources for the cutters are called out in the engine plans. 
The air and oil passages are drilled using a Guhring parabolic drill. This special shape promotes chip removal and allows the small deep holes to be drilled with confidence. 
The crankcase is equipped with a breather hole in the front of the crankshaft. This small hole creates just enough back pressure in the crankcase to force the oil into the sump. 





 

This is one of my favorite photos. The crankshaft with the master rod, slave rods and pistons. 
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_*Master Rod*_







The master rod tool is typical of the tools shown in the plans. Using this tool, it is possible to turn the overall shape, mill the flats between the support rails and mill the 3/4 degree taper to the rod. 
Nothing you couldn't design for yourself, but it's all documented in the engine plans for you to use. The tool design saves you a lot of time. 
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*Pistons *

The pistons are made from 2024 aluminum round for the better strength. There are two compression rings above the wrist pin. The oil control ring is below the wrist pin. The oil ring groove has 8 radial holes that provide a return path for the oil back to the crankcase. 
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*Piston Rings*

The piston rings are made of fine grain cast iron. 
There are two compression rings above the wrist pin, and an oil control ring below the wrist pin. The oil control ring is grooved between the two lands. A series of radial holes between the lands leads the oil to a set of radial holes in the piston skirt, and then back to the crankcase. 
The rings are turned and parted off from the stock. Then, are cleaved using a tool that is included in the plans. Fracturing the rings means there is no lost material in the gap. An additional tool is used to anneal the rings before assembly to the pistons. 
A chamfer on the bottom of the cylinders is used to compress the rings during assembly. 
The plans also include the use of mineral oil to help break-in the piston rings. 
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*Oil System*

The radial engines are equipped with a pressure pump and a scavenge pump. Both of these are gear pumps mounted in the same housing and driven from a common crankshaft gear. 
The pressure pump draws oil from the supply tank and forces oil onto a ring slot in the engine main bearing. This slot ensures the oil will enter the crankshaft passages regardless of crank position. 
The drilled oil passages carry oil to the master rod throw and then to the other main bearing. The oil is allowed to escape from the main bearing to lubricate the cam and cam drive gear. 
The oil then flows into the sump. From the sump, the oil is scavenged by a pump larger than the pressure pump. 
The oil is returned to the supply tank by the scavenge pump. 
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*Electronic Ignition System* 

The distributor rotor has a series of magnets, one for each cylinder. A hall effect sensor is pulsed by the passing magnet and sends a signal to the ignition electronics. The electronics controls the flow of current from the battery to the ignition coil. 
The distributor cover is made from black Delrin, a plastic material with superior characteristics to modern plastics under these high voltage conditions.​


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