Ok, so new guy with only some book knowledge so far on the rotary engines.
I have a johnson 40hp and two SACHS 303 engines.

I want to take the two sachs and make new end plates and a new two piece
crank to make the two sachs into one engine.

I need some help with crank design parameters, I see from the mazda cranks
that the rotor lobes are set 180 out from each other. However I do not know
how to balance the assembly.


I know on the single rotor how they are set up but on the twin rotors I do not
know the balancing procedure to offset the weight to the rotors.

All help is greatly appreciated.

David Jr.


The rotors
 need to be 180 degrees out of phase. That yields static balance.

Now you need dynamic balance which is tricky.

With just the two rotors the engine is in static balance.

For the engine to be in dynamic balance all masses must be located
in a single plane perpendicular to the rotating axis.

That of course is impossible in a 2 rotor.

One needs  two counter weights. One on the front and one
on the rear for dynamic balance.

The distance of the counter weights from the centre plane of the
engine is important as well as the radius of the counter weight masses
from the rotating axis. The attached  chart gives the formulas for these parameters.

A tire and wide wheel rim example is instructive. If you have a wide rim
the position of the weight in and out the width of the wheel rim from the out
side of the rim to the inside of the rim is important. It is best to add the weight
on the centre line of the wheel and tire for good dynamic balance.

You can make your own dynamic balance machine with a
MaxMite  if you have two accelerometer. One on the front bearing
and one of the rear. A Maximite could sample these accelerometers
about every several msec while the engine is being driven by an electric
motor. Solid state accelerometers are cheap these days as every smart cell
phone has them.

Google this:

"how to build a dynamic balance machine"

https://forum.sparkfun.com/viewtopic.php?f=14&t=29874

Paul Lamar

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