Grizzly

Can anyone shed some light on How the Rotating assembly is Ballanced?



There is some question as to how its done? here in the UK we have the gear to do the Job just not 100% sure how?



I have this old Pic of a Assembly being done but how do you account for the Oil in the Rotors? also how do you stop the Rotors Coming off the E-shaft? and how do you get the Rotors Spinning in the correct timing to the E-shaft?

michaelt

i have been trying to find this out as well.



I found a few links.



Mazda Motorsport link.

http://www.mazdamotorsports.com/webapp/wcs...bject=balancing



RX7 club link

http://www.rx7club.com/showthread.php?t=47...light=balancing





Does anyone else have any info?

Lynn E. Hanover

Allow me to speculate:



The rotors are already balanced about the bearing centerline, so there is no need to allow them to rotate on the shaft during a balance attempt. In fact, the rotors are not used in the balancing process. Just weights to replicate the rotors.



As you can see from your research, there is a specified value of weight to use instead of an actual rotor. I presume here that the specified weight includes a value for oil and seals less the apex seals and springs as the rotors cannot see their weight.



The permanent molds for the sand (plastic) casting cores for the interior of the rotors, appear accurate enough to allow for this use of a standard weight for the oil because the cores are then so close to perfect for each rotor that there is no need to spin up each rotor and then measure the actual oil volume it holds.



I have seen pictures of a rotor being spun up with oil being pumped into it, so some people are interested enough to the actual oil weight that they measure it for each rotor before the balance job starts,and adjust the bobweight value accordingly.



Taking weight off of the crank is the same as removing it from the adjacent rotor, so that would change the bob weight value, same as the oil weight.



Note that the counter weights are not close to the weight of the rotors. The rotors balance each other and the counter weights take out the induced rocking couple caused by the rotors not being in the same plane,

but displaced along the shaft. So, a big change in rotor weight requires only a small change in counterweight value.



Balancing the entire assembly as one piece would get you a better outcome than balancing the flywheel assembly as a unit and adding it later. This is because there is machining involved that is never dead on the target, and the smallest error will change the centerline of an assembly, and ruin the balance.

You have to add some indexing marks so that the the assembly goes back together in the same relationship each time. I would prefer that the assembly be balanced alone, first. Then add the flywheel assembly and get the balance done again dealing only with the flywheel assembly. (Flywheel, clutch assembly less the discs).



Balancing reduces stress on the bearings, and reduces unwanted harmonics in other components on the engine and in the chassis. Like the trans jumping out of gear now and then. Or dash lights having short lives. It is a must for high reving engines, but much less so for seldom used hard, street engines.



How does all of that sound?



Lynn E. Hanover

Nospig

All rotors ballanced by mazda up to rx8 were ballanced static. Rx8 rotors are balanced dynamically they inject a gel into them to compensate for the oil.

In my experence over the last 15 years , every engine balanced by some one other than mazda is f----d after theyve tampered with them . Results , broken apex seals , chattered housings and bad bearing life. Im sure half the rotary shops keep doing it cause they dont own rotaries them selfs or want the business again later.

If you want lighter rotors use 89 onward rotating assemblies and a lighter flywheel .

crispeed

Strange.

Because I've found the opposite to be true. I guess everyone's luck is different.

1Revvin7

Pre Rx8 rotary balance tolerances are extremely sloppy compared to piston engines. I believe there is a benefit to balancing every engine even if it won't see high rpms. Vibration/harmonics will fatigue engine parts faster.

RONIN FC

The internals are also moving only 1/3 the speed of a piston engine at the same rpm. Not to mention its non reciprocating.. But everyone should have known that already.



Im a sceptic of a normal shop balancing a rotary. Too many variables to ever be spot-on.

stuart wizy

heres my idea of how to balance my e shaft, please feel free to coment and tell me if im wrong.

the motor im building is an fc fully bridgeported, purely for drag racing only with a big custom 110 mm dia inlet manifold and 4- 50mm dia runners bolted straight on to a milled out inlet flange that match all 4 inlets which have all been ported much bigger in size, bolted to a q45 90 mm throtle body, I plan to run a t45 roller bearing turbo, ive milled the rotors out to 3mm and have a set of atkins 3mm tips.

Also i have lightened the rotors on the sides the same way racing beat machine theres on a cnc mill, hence the need for balancing.

I have access to manual and cnc -lathes, grinding machines, milling machines, boring machines and have access to a full machine tool inspection dept if anyone has any other ideas for machining any parts of the rotary engine for balanced high revs.



my plan for dynamicly balancing fully assembled e shaft, rotors, couterweights and flywheel:-



weigh the rotors dry then with oil and work out the oil weight

turn 2 spacers that are the same outside diamater as the rotor tips, inside dia (bore)bigger than the rotor bearing so it will pass over the e shaft when clamped to the side of the rotor.

turn 1 side of the spacer down until the deired weight of the oil is reached.

drill and tap the spacer on the same pcd as the 3 corner seal bores so allen bolts can be used to fasten the spacer on 1 side of each rotor through the 3mm slots in the rotor.

the spacer will then be on the same centre line as the rotor and will weigh the oil weight.

then fit both rotors with spacers fitted to each rotor onto e shaft along with both counterweights and the flywheel and dynamicly balance.

This is an idea that I had to get the oilweight on the same centre line of the rotor.

would it work???????



stu

uk

GMON

Hmmm, This topic always seems to be over complicated when it comes to rotarys. I dont understand why....



I think its the lack of rotary folks experience to rebuiling pistion engines where balancing is very common



Im getting one done right now, its not rocket science.



A) Get the rotors to the same weight.

-I have the option of spin balanceing each one but I really see no point as they dont spin fast enough to offset anything that much. Just not enough gain as they are not very far off.

-Why does everyone freak out about oil? Given centrepedal force and equal oil pressure and assumed similar volume on the inside of each rotor what is the point? Also, the cost of making them the same volume and comming up with some sort of process is a waste of time and money given the benifit. So I see the whole oil issue as bs that I dont need to worry about.



B) Once the rotors are the same weight and that weight is know the rest of the process is EXACTLY like doing a pistion engine.



-You balance the full rotating assembly minus the rotors.

-You "Polish"(not really polising its more or less sanding) each bearing surface, No thrust surfaces here

-Balancing includes the PP. The Shop I take my stuff to has found that aftermarket clutch assemblys are much further out of balance than the factory stuff.



Really pretty simple, I guess it all depends on the mechanical aptitude of the person doing the balancing. And for the comment somone made stating that balancing makes it worse, thats a bummer, might want to tell the person that did the balancing to use a calculator or maybe put down the pipe

GMON