18 Cylinder Engineering Description
The 18 cylinder is a conventional, overhead valve, double row, spark ignition, 4 cycle, radial engine. The engine is direct drive and is naturally aspirated.
The conservative design has a 6.7 compression ratio and is designed for manufacture with a minimum of specialized equipment. Speed is 400 rpm idle and 2500 rpm at full power. The engine is equipped with an oil pump that supplies pressure lubrication to the main bearings and both crank throws. The cam and drive gearing is completely lubricated. The engine operates on the dry sump principal with a separate large capacity scavenge oil pump for returning oil to the supply tank. The ignition distributor is equipped with an electronic ignition system. An Option is conventional mechanical points, but not recommended.
The crankcase of the engine is made of four sections. The nose section, the front power section, rear power section and rear housing. The nose section, which houses the front row cam and associated drive gearing, is machined from 6061 aluminum billet, piloted to the front power section and secured by 9 screws.
The front and rear power section are piloted together and secured by 9 additional screws from the nose section. The ball bearing that carries the thrust load, is located in the nose section.
Both power sections are machined from 6061 aluminum billet. Contained in the power sections are integral mounting rails that pilot the front, middle and rear main bearings into position.
The front of the front power section contains brass valve tappet bushings for the front row cylinders. The rear power section supports the middle and rear main bearings. At the rear of the rear power section are brass valve tappet bushings for the rear row as well as an intake manifold for nine intake pipes. The oil sump is mounted by two brass tubes threaded into the bottom of the rear power section. The cylinders are secured to the crankcases by eight threaded studs.
The rear housing is a 356-T6 aluminum casting. The casting has provisions for two distributors and carburetor mounting. The rear section casting is piloted to the rear of the rear power section and secured by ten screws.
The cylinder barrels are machined from 12L14 free machining steel. They are provided with deep cooling fins machined integrally with the barrel. The barrels are screwed into the cylinder head and each cylinder flange is attached to the crankcase by means of eight studs. The cylinder barrels can be gun blued for corrosion resistance.
The cylinder heads are machined from a single piece of 6061 aluminum billet. The two valve towers are integral with the lower portion of the head and are machined using a special fixture. Provision is made for one ignition spark plug. The rear portion of the cylinder head is provided with a mounting surface for the intake manifold and exhaust stacks.
The crankshaft is of the double throw type and is made from 8 pieces. The two throws are 180 degrees opposite from each other. The various shafts are secured using a broached square hole and secured by taper pins. The crank throws are made from 4140 steel, the shafts are made from 303 stainless steel. No heat treatment is required. The crankshaft is supported by three plane bearings of large diameter. The main bearings are made from 660 bearing bronze. The front of the crankshaft is provided with a drilled hole for venting of the combustion gas.
There are two master rods, one for each crank throw, these are 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 rods are 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. Oil is returned to the crankcase by an oil control ring with two integral lands and twelve radial holes. The piston groove has eight radial holes. The piston pin is of the floating type, with aluminum plugs at each end to prevent scoring of the cylinder wall.
There are two cams, one for each engine row of cylinders. The cam rings, which actuate the valve tappets, are machined from a single ring of 4140 steel, heat treated to 46 Rc hardness for wear resistance. Each cam is supported by a ring that is an integral part of the front or rear main bearing and are held in place by three plate mounted buttons. Attached to the cam ring is a purchased internal tooth ring gear. Each 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 engine has a single inlet and exhaust valve of the poppet type, 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 also stainless and secured with a pin and keeper arrangement. The valve train is equipped with solid ball nose tappets, push rods and pivoted rocker arms. The rocker arms are provided with a screw adjustment and lock nut.
Oil is supplied from an external supply tank through transfer tubes to a positive displacement gear pump. The pump is mounted to the middle engine main bearing and is driven directly from a gear mounted to the engine crankshaft. Oil is forced, under pressure, into the center main bearing. The crankshaft is provided with drilled passages to provide positive lubrication to both crank throws and the front and rear main bearings. Oil is then directed to each of the cam drive gears. The cylinder walls, crankshaft thrust bearing, piston pin and tappets are lubricated by splash. Positive crankcase pressure directs the oil to the sump located between the bottom two cylinders of the rear row. A large capacity gear scavenge pump, also driven by the engine crankshaft gear, removes oil from the sump and directs it back to the supply tank.
The rear section of the crankcase is equipped with a mounting flange for the carburetor. Air enters the carburetor at the engine centerline and is directed to an impeller behind the rear row cam housing. The impeller ensures the fuel is completely vaporized. Nine intake pipes are fitted with " O " rings at their crankcase ends to allow for thermal expansion. Each of the nine intake pipes are split to supply both a rear row cylinder and an adjacent front row cylinder. The intake and exhaust pipes are brazed to a mounting flange and secured to the rear of the cylinder head.
The two distributor, one for each row, are driven by a set of gears giving a 2:1 reduction to the distributor shaft. Each distributor rotor is equipped with 9 magnets that trigger the hall effect sensor. The ignition system is a CDI ( Capactor Discharge Ignition ) that provides a hot spark. The ignition voltage is sent to the top of the distributor and on the the correct cylinder. There are three spark plug options to choose from.
The distributor cap is made from black delrin and secured to the housing with screws. The ignition wires are also positively secured to the distributor cap contacts with screws.
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