1Revvin7

True, however when we build piston engines here they are within 1/2 to 1/4 gram, the last rotary I had done was off by 47 grams!

crispeed

Rotaries have a wider margin in balancing in comparison to piston motors. That's why when you take a perfectly stock balanced motor and have it balanced to closer specs you gain many benefits. One of which can be felt alone with the diferences in smothness in balanced vs stock. You might gain a couple of horsepower but your lap/et's are going to show the real gain not to mention the gain in reliability at extreme levels of operation.

What feaks me out the most is that some of these so called big name companies project rotary balancing to be some form of black magic art that only they can perfom and the cost of getting it done from them is rediculos. It's much easier and less time consuming to balance a rotary motor versus a piston motor any day.

crispeed

Exactly!

GMON

I assume both. They had 3 tiltons laying on a shelf with drill marks on them. I asked them what the deal was and they told me they have not seen an aftermarket clutch/pp come through that was balanced to their liking. Hence why they always throw that stuff into the mix.



@ $1500 a pop you would think the balance would be better. Im just going off what they told me

Lynn E. Hanover

In the case of a pressure plate that uses coil springs for pressure, and that has drive straps to locate the pressure surface, it might be possible to balance that device while bolted to an already balanced mounting or flywheel. Assuming some very accurated machining and hole locations.



The racing pressure plates use a diaphragm spring to apply pressure to the pressure surface. That spring is free to move a bit relative to the centerline of the cover.



The spring gets wider when the throwout bearing pushes it from conical to flat. So it has to have some motion available.



The pressure surface is free to move relative to the cover. Each floater is free to move relative to the cover. The pressure surface may be driven by splines or a number of vertical posts.



The available movement is minor but would subvert any attempt to spin balance the system. If the pressure plate were to be disassembled and the diaphragm spring, pressure surface, and all of the floaters removed, then only a locating machining error could subvert the balance of the spacer and cover.



There are usually balance marks on my covers, and the manufacturers are not all idiots, so I am guessing that my covers and spacer are balanced, so long as I don't assemble the internals.



The balance will go off a bit once the clutch is assembled and installed. Live with it. It is not a big problem and the smaller diameter covers make the problem even smaller. Send me all of the 5 1/5" clutches that nobody can balance. I can use them.



Balancing complete assemblies eliminates the poor maching for centerline location. Once balanced the assembly needs to be permanently marked so that is always assembled in the same relationship, or the balance is lost. Dont mark it by drilling holes in it.



Lynn E. Hanover

heretic

The rotors may be rotating at 1/3rd engine speed, but they certainly are orbiting at 100% speed.

RONIN FC

Which if it was of great consequence, would put great wear and stress on the stat and rotor gears.

And we dont see too much of that so...

goldedge

If balancing is not important in a high rpm rotory engine why does the load

on the eshaft double from 7500 to 8500 rpm creating shaft flex?

Lynn E. Hanover

That is two different things.



The shaft flex is still there even in a perfectly balanced rotary. It is a function of the very heavy rotors being displaced along the shaft rather than being in the same plane. So, the rotors balance each other but being offset on the shaft, there is a wiggle induced in the ends of the shaft. The ends tend to move in a small orbit.

Called a rocking couple.



So, we add the front and rear counterweights. Note that the counterweights are not heavy enough to balance the rotors, but only have enough mass to take out the rocking couple. So if the rotors are lightened,

the reduced rocking couple requires that the counter weights be lightened slightly as well.



The stress loading that seems to ocurr just between two RPMs is just a small picture of a typical stress curve that goes up with RPM. It is an exponential function, so stress increases at the cube of velocity. So, 4 times the 9 pound rotor weight at one RPM may go to 16 times the rotor weight 4,000 RPM up that curve. So, a 36 pound rotor may have enough bearing size to survive, and is not enough stress to bend the crank a noticable amount, where 144 pound rotor might be in danger of failing that same bearing, and is certainly enough stress to bend the crank and endanger the rotor tips and main bearings.



This where a center roller bearing and very light rotors are required to survive even a few drag racing passes above 11,000 RPM.



In the rotary, the heavy rotors allow for a balance to be off more than a piston engine and still seem very well balanced. You could misbalance the rotary (rotor) by an ounce and not notice it because it is such a small percentage of the total rotating mass. In a piston engine, that same ounce missing from a counter weight would shake your eyes out.



The total weight being balanced is less, and the ounce is a higher percentage of the mass being spun up.

Piston engines cannot be balanced even in the same kind of thinking as the rotary. Part of that mass is not spinning at all, but hopping up and down. So they use terms like a 72% balance and the like. Note the large soft motor mounts in the piston powered cars. The 4 cylinders have a nice 4th harminic hop that can only be removed by an additional shaft spinning in opposition to the crank. And some advanced 4 cylinders actually have such a shaft. I once put a Chevy 283 V-8 in a Falcon station wagon and bolted it solid to the chassis.

The sun visors would not stay up, the glove box door would not stay closed and all of the dash lights all died in one week. But it would burn rubber in top gear. Because it was so light, not because the engine was all that strong.



Years ago, there was a band of nut cases from Canada who towed their race car with an old Ford V-8 powered school bus. Their Dad came with them every weekend. They came in late in the afternoon one Saturday and we asked about them. The Ford had lost a rod bearing and broken a rod. The free end of the rod punched a hole in the side of the cylinder and let coolant into the oil pan. They drove it to a rest area.

Removed the pan. Dad made a wood plug to pound into the hole in the cylinder and hold the piston near the top end of the bore. They removed the pushrods for that cylinder. They added a piece of card stock to the big end bearing to lock it up so it could not punch any more holes. They put the pan back on and drained out the coolant and drove on down the road.



The only problem was that the engine was over a pound out of balance. Dad said that 45 MPH was about all they vibration they could stand. They were back the following weekend with a fresh engine in the bus.



Lynn E. Hanover

Jeff20B

My dad's '68 Impala once had a spark plug wire burn through its insulation on an exhaust manifold. Cheap Autolite orange wire set with lousy routing. With that cylinder dead, it vibrated a lot, especially above 45MPH. I pulled the wire away from the manifold, wrapped a little electrical tape around it, and it smoothed back out.