Hand Machined Miniature 9 Cylinder Radial Gas Engine

SKU: MS 9 cylinder

NOTE: This engine is hand machined and only 1-2 are built a year! 8 month wait time.

9 Cylinder Radial Engineering Description:

The 9 cylinder is a conventional, overhead valve, single row, spark ignition, 4 cycle, radial engine. The engine is direct drive and is naturally aspirated.

The design has a 6.7 compression ratio and a 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 crank throw. 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.


The crankcase of the engine is made of three sections. The nose section, power section and rear section. The nose section, which houses the cam and associated drive gearing, is machined from 6061 aluminum billet, piloted to the power section and secured by 18 screws. The ball bearing that carries the thrust loads, is located in the nose section.

The power section is machined from 6061 aluminum billet. Contained in the power section are integral mounting rails that pilot the front and rear main bearings into position.

The front portion contains bearing bronze valve tappet bushings while the rear portion has provisions for 9 individual intake pipe mounting locations. The oil sump is mounted by two brass tubes threaded into the bottom of the crankcase. The cylinders are secured to the crankcase by eight threaded studs. The rear section is an aluminum casting. The casting has provisions for the distributor and carburetor mounting. The rear section casting is piloted to the power section and secured by 9 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 cylinders can are gun blued for corrosion resistance.

The cylinder heads are machined from a single piece of 7075 aircraft aluminum billet for added strength and have pressed in aluminum bronze valve seats. 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 single throw type and is made from 5 pieces. The output shaft and rear shaft 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 two plane bearings of large diameter. The main bearings are made from 660 bearing bronze. The front of the crankshaft is provided with a ball thrust bearing in the nose section of the crankcase. The front of the crankshaft is provided with a drilled hole for venting of the combustion gas.

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.


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.


The cam ring, 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 by a ring that is an integral part of the front main bearing and held in place by three plate mounted buttons. Attached to the cam ring is a purchased internal tooth ring 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 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.

Lubrication System

Oil is supplied from an external supply tank through transfer tubes to a positive displacement gear pump. The pump is mounted to the rear engine main bearing and is driven directly from a gear mounted to the engine crankshaft. Oil is forced, under pressure, into the rear main bearing. The crankshaft is provided with drilled passages to provide positive lubrication to the crank throw and front main bearing.

Oil is then directed to 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. 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. A seperate plate and lip seal separates the oil pump area from the intake space.

Intake System

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 oil pump 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. The intake and exhaust pipes are brazed to a mounting flange and secured to the rear of the cylinder head.

Ignition System

The distributor is driven by a set of bevel gears giving a 2:1 reduction to the distributor shaft. The distributor rotor is equipped with 9 magnets that trigger the hall effect sensor. The ignition system is a CDI ( Capacitor Discharge Ignition ) that provides a hot spark. The ignition voltage is sent to the top of the distributor and on 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.

Click on picture for large view.

This engine is a hand machined 1/5 scale model of a 1925 985 wasp Jr. with a 32 inch propeller. Design by Lee Hodgson. Estimated machining time for this engine is 1,500 hours! At $8,995 that equates to $13.33/hr for master machinist work!
9 Cylinder Engine Specifications:
11.25 inch diameter
9.0 inch length ( without carburetor )
1.00 inch bore x 1.125 inch stroke
7.95 cubic inch displacement
Compression ratio 6.7 : 1
Approx. Weight : 9.37 lb. without carburetor, oil tank or club
Fuel - 89 Octane unleaded
Oil - 50 wt - Nondetergent Aircraft Oil
Pressure oil pump
Fully Pressurized main bearings
Fully lubricated cam drive gear
Dry sump with scavenge pump
Direct drive
4 Cycle - Air-cooled
Naturally aspirated - No supercharger
Rotation: Clockwise viewed from rear
Spark ignition - 1 plug per cylinder
CDI electronic ignition with distributor