Building the 4 Rotor- some details...

Removed from the front of the rear engine are the front cover, oil pump, thrust bearing, counterweight, water pump, etc. Pretty much wiped clean with the exception of the stationary gear and modified rear ecc. shaft. The 3/8" plate bolts to the rear engine first, as internal bolts are needed to seal passages exposed when the front cover is eliminated from the rear engine.

A round donut shaped pilot ring was machined, which lightly pressed into the recess in the exposed front stationary gear on the rear engine, and into the seal groove of the rear stationary gear of the front engine. This pilot ring served to accurately align the front and rear engine's eccentric shaft bores, while allowing the e-shaft coupling to pass thru it's center. O-ring grooves in the pilot ring seal the front engines' rear stationary gear to the adapter plate, preventing oil leaks from inside the front engine's rear housing.

The 2 lower exposed (outside bottom) tension bolt holes are bored out and the stock bolts replaced with very long bolts that go thru both engines, to pre-tension the lower part of the engine, as I used only front and rear motor-plates, and no mid-plate support.

At the heart of the design is the coupling, which has to take a lot of abuse, yet remain small enough to fit thru a main bearing to allow assembly. The coupling design requires welding up the eccentric shafts (or building new shafts from scratch), which lengthens the full diameter portion of the shaft adjacent to the main bearing journals, so that the coupling can be machined into them. It is a tapered/pinned design that requires a draw bolt passing thru the bored out center of the front ecc. shaft, threaded into the male half of the coupling (which is machined into the rear e-shaft), to draw the two ecc. shaft tapers together. The tapered portion was about 1-1/2" long, with a series of (12) 3/16" dia. x 2" long aluminum pins arranged in a circle about the taper parting line. As the pin holes are bored parallel to the e-shaft centerline, the parting line passes thru the pin at an angle, with 1/4" of each end of the pins firmly rooted in each of the shafts. The drawbolt thru the bored out center of the front e-shaft pulls the coupling together, and allows the front engines' thrust bearing to work for both shafts.
By using the tapered/pinned design, the loads on the coupling are effectively spread out over a much larger cone shaped area. Less stress concentration, than what would have been present with any other type of useable coupling we could dream up, was an added bonus. All this in such a compact and relatively inexpensive design.

Because the design removes what would have been the 2 middle counterweights, the two engines were indexed the same (#1 rotors for each fired at the same time). This puts the two middle eccentrics 180 degrees (in rotation) from one another, thus canceling the need for center counterweights to maintain balance.

For the oil pump, I use the big oil pump on the front of the front engine, which feeds both engines, and modify the drive ratio. By machining off and welding the toothed part of another oil pump sprocket onto the eccentric shaft sprocket, it is possible to drive the oil pump at twice speed (1:1 instead of 1/2 speed), which roughly doubles the volume. The special drive chain required is made from parts of 2 chains put together, as I could not find a source for the odd pitch chain.

A separator/de-airiation plate was made that fit across the entire bottom of the assembled 4 rotor, which helps seal the area between the engines for the full length, baffled and gated custom built oil pan. A special larger pickup tube is made and the oil circuits "ported" to ease the demands on the pump.

The water pump housing is modified so that the output can not flow into the front engine from the front housing, but instead is re-directed into an external distribution manifold. From here, the coolant is split and directed into the top of the center housing of each engine. The modified rotor housing coolant flow is into each center housing from the top, clockwise (from the front) around to the top on the right side, cooling the combustion side of the engine first, then to exit ports that return the coolant to the radiator. No thermostat is used, only center housing outlet restrictors to regulate coolant flow rates and engine temperature.

For the ignition system, my 1st design fired only 1 plug per rotor, and allowed using the normal point type distributor. Points were adjusted to fire leading/trailing at the same time, with leading plug wires going to the front engine, and trailing wires to the rear. A more modern ignition would be a direct fire using double posted "waste spark" coils, one post for the front engine, one post for the rear. 4 coils would be used.

Starting the beast was harder using 1 plug per rotor, so a 24v starting system was used. The added voltage increased cranking speed, but the starter would overheat at anything over 20 secs.(melted the solder in the brushes). A system that uses 18 volts cranks almost as fast, as is not nearly as hard on the starter. If you use both plugs per rotor, the 18v system will work for you.

During the duration of the project, which included quite a few nites racing spread out over a year and a half, the couplings experienced no damage at all. The draw bolt, which I felt would be the first external indicator of failure, maintained it's assembly torque with no sign of any loosening. When the engine was finally torn down (after an oil line was torn off during a race), the coupling and all it's components looked like new. As proof of this, when the engine was assembled, the coupling pins and taper was coated with loctite, which I felt would fill any minor discrepencies, and improve the strength of the coupling. Upon diassembly, the shafts were quite hard to seperate, as the loctite bond was still intact.

For the type of racing that the engine was built for, eliminating as much rotating mass as possible is a much sought after goal. The effects on accelleration can be very surprising. By joining the two engines as I did (using only 1/2 the normally required flywheel and counterweight mass), the engine rev'ed much faster than a single engine by its self. Although the exhaust note might be more pleasant if the engines were phased 90 degrees from one another for an even firing order, the reduced mass and synchronized peak torque pulses make for less stress on the coupling, and the reduced rotational inertia over that of two separate engines far outweigh any performance advantages of the smoother sounding 90 degree firing order.

The coupling design...

Here are some basic descriptions of the key parts needed to build your own 4 rotor. We will start with the coupling design.
The basic geometry is that of a tapered/pinned coupling, with a male and female component. The male half is machined into the front of the rear e-shaft, and the female half is machined into the rear of the front e-shaft. The total length of the mating tapers is exactly 1.000". The major diameter of the taper is 1.400", and the minor diameter is 1.200". Angle of the taper is 5 degrees, 43 minutes.
Arranged about the parting line of the taper is (12) 3/16" aluminum pins, evenly spaced on a 1.300" pin circle diameter. These pin holes are bored parallel to the e-shaft centerline. Total length of each of the (12) pins is 1.500", with .250" of each end of the pins rooted in the front and rear e-shafts. A 3/8" dia. draw-bolt passes completely thru the center of the front e-shaft, anchored in the internally threaded male component of the rear e-shaft. Ours was conviently made from a section of 3/8x24 fine thread B-12 redi-rod. A nut over a hardened washer in the center of the front pulley was torqued to 35 ft/lbs to draw the two e-shafts together. A bit of sealer is a must to prvent oil leaks.

The pin hole drilling jig...

We made a drilling jig to locate the (12) pin holes for boring. This ensured that both halfs of the coupling had exactly the same pattern, and allowed rotation of the pin pattern prior to drilling to adjust the indexing of the shafts. The jig was made of solid steel, with the center bored out to the same diameter as the main bearing journal, so that the jig could be placed over the end of the shaft for a full 2". (3) radial set screws were arranged 120 degrees apart to allow precision adjustment of the pattern for eliminating run-out. The open end of the jig was slit in (3) places, each 120 degrees apart, and 3 more screws were used to close the slits to secure the jig to the shaft.

The front eccentric shaft...

The rear section beyond the rear main bearing area must have material added so that the front half of the coupling can be machined into it. We mounted the shaft in a lathe, and added the material using a MIG welder w/ standard steel wire. Add enough material to the former flywheel mounting section to maintain the full 1.690" diameter of the rear main bearing journal for a total length of 3.050" from the face of the rear rotor journal. After everything slowly cools off, the added material can be machined to the same dia. as the main journal, and faced off at 3.050" total length (from the rear rotor journal). Do not machine the internal taper for the coupling female section yet, until after the (12)pin holes are bored. After drilling the (12) pin holes to a total of 1.255, the female taper of the coupling can be machined out of the inside of the shaft. The length and major/minor diameters are listed above.
The center of the shaft must be bored out to allow room for oil to flow around the draw-bolt that must pass thru the center of thr front e-shaft to draw the coupling together. We drilled the center of the front e-shaft out to about 9/16", using a drill bit that was modified by welding a long extension to the shank.

The rear eccentric shaft...

The front section of the rear e-shaft is built-up using the same method as used for the front e-shaft, except that it is built up to the full 1.690" diameter of the main bearing journal for a total distance of 3.690" from the front face of the #3 rotor journal. This dimension includes the 1.000" long male component of the coupling taper, which is not machined to it's finished diameter until after the (12) pin holes are bored. Use the same method to locate and drill the pin holes as was used for the front e-shaft, except pay close attention to the positioning of the holes as they are used to index the phasing of the shafts. After the (12) pin holes are bored to a total depth of 1.255" ea, the male taper can be machined into the front of the rear shaft. The center of the male taper is drilled and tapped to 3/8"x24 internal thread, required for anchoring the draw-bolt

The pilot ring...

The pilot ring is machined from a 4.750" dia. x 1.150 long solid blank of solid steel. Although aluminum may work, we felt that since this ring pilots the 2 engines main bearing bores in proper alignment, the extra weight was an acceptable trade-off.

Here's a crude sketch of the pilot ring (from my old shop notes) for my friend in So. Africa.....

The 3.740 dia. side of the pilot ring fits into the area of the rear stationary gear formerly occupied by the E-shaft's rear main seal, in the front engine.
The 2.365 dia. side of the pilot ring fits inside a recess in the front stationary gear of the rear engine.
I'm still trying to remember what the 3.125 ID represents in the lower portion of the drawing.

The mid-plate...

The oil pump drive sproket...

Water pump / cooling...