When we built racing VW engines we used the coldest plugs because plugs were free. We installed a thin sheet copper gasket instead of the fat thing that comes on the plugs, because gaskets are free. You can use anything you want.

 

The result is that less volume is available in the cold plug (Surface gap) and the plug going deeper into the plug hole takes up more volume. So, more compression all around. So plugs can make a big difference.

 

If assembled by the book you should have over 100 pounds of compression. If the starter is spinning up the motor to spec and the throttle was wide open during the test. Note that the spec does not include the starter motor spinning up a prop for the test. So your result will be below spec if the prop is mounted, and a real car battery with real car battery wires in the same length are not in use.

 

Car batteries and garden tractor batteries are rated at 70 degrees. Below 70 degrees your result will be  less effective plate area.

 

The rotary is cold blooded. Old people talk for its hard to start from cold. RX-2s and RX-3s had a bottle of anti freeze on the fire wall. In cold weather, some of this antifreeze would spray into the engine during cranking.

First, to take any frost off of the apex seals. As in one revolution, the seals would be glued into the bottom of their grooves by the frost, and no start was possible, because of no compression, and no "Heat Of Compression".

 

Second, it took up some volume, and assisted in sealing the engine, so it could develop some heat of compression. No heat of compression, no vaporization, and no start. Fuel droplets stuck to ice cold iron will not even light. It needs to be a near gas to get an energetic explosion so as to spin the engine fast enough to run. So on cold days you get an engine that seems to run so long as the starter is helping it, and it stops when the starter stops.

 

Sound familiar?

 

On the race car I gave it three complete strokes of throttle to get full accelerator pump strokes worth of fuel, before cranking. The fuel takes up volume and helps seal the compression in long enough to make some heat. I do no tolerate a slow starting engine. In cold weather 5 or 6 strokes is required. Even then the engine may run only at idle speed or just above. Fuel that will not atomize looks like way too lean a mixture to the engine. So fast idle is OK until it builds up some heat and can take a bit of throttle.

 

The side seals make the rotor look like a piston engines piston of about 6" diameter with a compression ring with 6 end gaps. That would be hard to start as well wouldn't it?

 

Leak rate. The rotor is slow moving with a long dwell period. Smokey would have loved these. So there is a long time available for the compression to leak down as the engine turns during starting. So the low compression is made worse by the rate of leak.

 

I build engines with zero end gaps on the side seals. Never a problem. The rotor gets a bit bigger as it heats up and you get more end gap anyway. So long as the side seals and the corner seal pop back up after being fully depressed into their slots, you are good to go. Engine starts are so fast and easy, even the driver could do it.

 

Engine compression testing is very nearly of no value. Test compression after the engine is at operating temperature. High oil temps and at least 180 degrees for water. If the prop is mounted your result will be lower than actual. Because of cranking speed.

 

My Fiat engines had zero leak-down and 245 pounds of compression after each dyno run.

 

How much blowby you get at loaded full throttle is the measure of leakage. That 1/4" breather tube on the filler neck needs to be replaced with at least a 3/4" ID tube into a catch tank. The gas flow rate through this tube is low on the street car at 2,000 RPM. It is not acceptable at 6,000 or 9,000 RPM. It will carry oil droplets into the  catch tank because of high velocity flow. Slow it down with a larger ID pipe and hose. We could do a weekend of hard use and get nothing in the catch can. If you get 1/2" of oil in the can, its time for side seals. Your results will vary. Airplane use is harder on the engines than race car use duty cycle wise.  

The bigger pipe and hose takes the pressure off of the lip seals as well, so fewer oil leaks everywhere. 

 

An oil squirt can with a 1/2 gasoline 1/2 motor oil mixture will usually get things going pronto. It will start much better after 8-10 hours of hard running. Just tell the tower you are starting a big radial. 

 

Lynn E. Hanover