goldedge

[quote]

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.

[/qoute]



Thanks for the reply Lynn,

Excellent information I now understand the rocking couple concept,

( I think you should adopt me <g> )



Carrying the balancing concept further, assuming we could achieve perfect balance

thereby eliminating the rocking couple effect etc,

wouldn't the thrust effects of compression and combustion still induce a varying loading/stress curve

on to the excentric shaft?



How does the loading stress curve on a 2 rotor engine compare to a three rotor?



Regards

Michael

CGeek2k

If I understand this correctly, you can never remove the rocking couple alltogether since the center of mass of the rotors is offset from the rotation axis of the e-shaft. I think that you are right about the compression and combustion effects though.

Lynn E. Hanover

Excellent information I now understand the rocking couple concept,

( I think you should adopt me <g> )



Carrying the balancing concept further, assuming we could achieve perfect balance

thereby eliminating the rocking couple effect etc,

wouldn't the thrust effects of compression and combustion still induce a varying loading/stress curve

on to the excentric shaft?



How does the loading stress curve on a 2 rotor engine compare to a three rotor?



Regards

Michael



Well, the more pistons, or the more rotors, the smoother the engine will be from all problems. If you ever got to ride a BSA gold star 500CC single. Or a similar Arial Red Hunter, you could take your weight off of the pegs at a light, and if the idle were set just so,.........the front wheel would hop off the ground in sympathy to an engine harmonic. So a single anything is the worst case. Piston or rotor. There are some single rotor engines about that have been constructed from 12A or 13B parts, looking for a lighter engine and around 100 HP for airplane use.



These engines can be 100% dynamically balanced (counterweights equil the rotor weight and arm length. And still they are very rough. The single rotary is smoother than a 100 HP single piston would be.

Imagine a 100HP single piston Motor Cycle. Ouch.



At any rate, this apparent imbalance (it isn't) is, as you suggest, a result of a rotor going into compression, and slowing down, and then after ignition, accellerating again. In a system with enough mass in the flywheel, this is nulled out, (Energy is stored in the flywheel) and is not at all noticable. But who wants a 40 pound flywheel?



In the race car, and on aircraft where a light weight wooden prop is used along with a reduction unit, (Like running in 2nd gear) allowing the idle to get too slow will begin to shake the gearbox to pieces. As the crank slows and accellerates. Just bumping the idle to above 1,800 RPM keeps everything going in the right direction, and all is well again. The very light flywheel of the race engine makes this a big problem.



The three and four rotor engines seem smoother no matter what flywheel mass is used. The rotors make up a huge amount of mass and double as the flywheel.



This reply is in the wrong frame, but I could not get the reply function to work there. I get a 502 gateway failure???. Sorry.



Lynn E. Hanover

diabolical1

while we're on this topic, does any have or have links to a breakdown of the different rotor weight classes (A-E) throughout the years? i'd love to get my hands on that because i went to get my rotors balanced yesterday they turned out to be 25 grams apart, so i just left them. however, the part that got me was their actual weights. one was 9.953 pounds and the other was 10.008 pounds - Mazdatrix has them listed as 9.6 pounds. so i just want to see if the weight classes account for 0.5 pound difference, or if this engine was assembled with older rotors at some point in it's life.



thanks.

PDF

There is 20-25grams difference between each letter. A being the heaviest and E the lightest.

pluto

Actually, there's more than 20-25grams difference since we do balancing on our engines. Each adjacent letter can be as much as 60 grams off and same letter can be off as much as 20 grams. This was verified many times while balancing our engines. Additionally, some flywheels that comes from Mazda were off by as much as 120 grams.



I didn't believe in balancing until I start talking to some of the high rpm NA rotary drag racers. I was told that just by balancing the engine, they gain as much as 5% in hp. The engine also last longer because there were less vibrations in the engine and drivetrain.



There is also a reason why there were so many short live mazda remans having bearing failures because of balancing issue. I was told that mazda who contracts their engine rebuilds in the state doesn't even balance their engine when they assemble it at their facility. I always tell my customers to balance the engine if they wanted the engine to run smoother and last longer.



We charge $250 for our balancing process (balance everything to within 5 grams from each other) and in my opinion, it is probably the best option to get for a well build, long lasting engine.

crispeed

I don't even believe balancing would have help those motors. The idots who have been doing the remans as of late need to get shot. I've never seen so much shady work in a long time. Rotors went dents. Excessive side seal clearances even with new side seals. Bearings that looked like marbles ran true them just to name a few.

j9fd3s

yep, same here. we showed the pics to our rep, he was wondering why he was doing a third warranty claim in 5000miles.....



i wouldnt expect any action/changes from mazda

RONIN FC

Ive always heard of mismatched counterweights on the remans.

j9fd3s

that was a problem for a while, but they seem to have moved on to leaving o rings out