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-   Rotary Engine Building, Porting & Swaps (https://www.nopistons.com/rotary-engine-building-porting-swaps-55/)
-   -   Engine Balancing (https://www.nopistons.com/rotary-engine-building-porting-swaps-55/engine-balancing-36201/)

Dazz 03-25-2004 02:43 PM

This is something that I find very interesting, and am wanting to get an engine fully balanced, but need to know when doing the balancing what allowances need to be made for simulation the weight of the oil in the rotors and eccentric shaft, along with any other weights that may need to be taking into account?



Does anyone have any experience with engine balancing and what tips can you give?



The engine in question is a 12A from a1984/85 SIII RX-7 (1st gen) which will be bridge ported.



Thanks for any info you might be able to share.

j9fd3s 03-25-2004 04:04 PM

well thats the tricky part, you can assume that the eshaft is gonna be full but the rotors are a big question mark.



you may be able to get a rough estimate of it by looking at the oil level when its running at various rpms

Dazz 03-25-2004 04:55 PM

It needs to be measured much closer than that, down to a few grams really if the balancing is to be accurate and worth the effort.

Dazz 03-28-2004 04:41 PM

Is there nobody who knows anythng about this at all?



Or do they just not want to share it https://www.nopistons.com/forums/pub...1047683358.gif

thekid 03-29-2004 10:08 AM

The Mazda Motorsports catalogue (I believe you can view it on the web) gives a balancing procedure with weights of various rotors, bob weight values, how much to offset the bob weight, and how much extra to add for oil in the rotor.

TyresmokinRx7 03-29-2004 10:13 AM

Where's Dazz from. U.S or AUS.

Dazz 03-29-2004 03:21 PM

I'm in Australia.



Thanks for the pointer The Kid.

boyrotor 04-15-2004 11:51 PM

"When the oil level insid the rotor is higher that the outer diamer of the stationary draining vane, the surplus oil is drained through radial and axial passages which are interconnected. This maintains constant oil level, and thereby eliminates engine vibration due to changes of oil quantity in the rotor." - Kenichi Yamamoto in his 1971 book 'ROTARY ENGINE' Published by Toyo Kogyo

kahren 04-16-2004 12:34 AM

i was wondering if they took the from pulley into consideration when balancign the motor and i guess they do after i foudn these holes drilled in there...

Goopy 04-16-2004 09:46 AM

There should be a good understating on what you want ?

Oil volume or oil pressure?



Oil passages should always be size matched..Stay as close to oem as possible..then use royal purple oil (viscosity is key)



And yes to properly balance an engine you should balance everyhting that is on the E-shaft.



Clutch, pplate, flywheel, rotors, front weight, front pulley,



You would be surprised if you knew what 1 gram of exes or off weight is at 10000 RPM....



The blancing art is best defined on the Rx8's...a buddy of mine just picked one up the otther day, we poped his hood in my driveway and fired the engine up...

It was unbelevable to see the engine hardly move...the only thing that gave it away was the alt belt..the the precision balancing that the mazda engineers did on the RX8 is awsome...and also as it was reved.

RONIN FC 04-16-2004 08:24 PM

Wow, this has been coming up alot lately? Its hard to find straight answers.

Speedworks 09-30-2006 06:30 AM

Can an excentric shaft and/or complete assembly be balanced like an ordinary piston engine or do you need special tools?

Nospig 09-30-2006 06:01 PM

Up to rx8 mazda balanced rotors static , now they are injected with a gel and balanced dynamically.

Every engine i have worked on that has been balanced by a so called expert has had a nasty vibration at some rev range . One rotating asssembly was taken back 3 times each time hed say now its perfect. B S. When it died an apex seal broke ( shattered ) suprise suprise oppisite to that seal a bunch of balancing marks hed made.

Engines with the original rotating assembly or untampered with matching parts work best.

But from a shops point of view , an unbalanced engine isnt going to last as long , and they can charge you for it. Vibrations = broken apex seals , chatter marks and bearing failure.

Speedworks 09-30-2006 08:19 PM

Thanks, but I'm putting together my own engine. I'll be reusing all parts except for the front iron. New housings as wel.

new eshaft and rotor bearings as well.

I'm in Europe and rotary builders are rare to non excisting. I need to know if the engine can be balanced like a normal piston engine...

RONIN FC 09-30-2006 08:25 PM

Ive tried making that point many times. People just insist that having a shop balance their assembly is better, but yet no one can tell me how they can account for different oil volumes and casting differences inside the rotor. Even different kinds of oil can have a different weight.



Now, if youve had rotor lightening and such, I can see a balance job bieng needed.

Speedworks 10-01-2006 02:07 AM

Thanks Ronin. My car is a turbo so in that perspective not making over 9000 rpm regularly like NA's. I'm just trying to make sure I do the best job I can do instead of having to deal with something as stupid as that afterwards and need to hear 'I told you so'.



I guess the fact that I'm reusing 98% of the original parts will contribute to that.I hahve little wear on the bearins now and will be masuring the e shaft in a few days..

Nospig 10-01-2006 04:52 PM

IF all the parts are correct for your engine , the factory balancing is fine. With the rotors they are stamped with A B C or D you can use an A with a B or B with a C etc but do not use A with C or B with a D etc and they will work just fine.

GMON 10-02-2006 03:07 AM


Originally Posted by Dazz' post='493083' date='Mar 28 2004, 02:41 PM

Is there nobody who knows anythng about this at all?



Or do they just not want to share it https://www.nopistons.com/forums/pub...1047683358.gif



Ive had one done. Dont worry about the effin oil. The rotor spins. Oil seeks a level on inside the rotor and is replenished at a constant rate relative to each rotor.



But yeah, anyone that can do a piston engine can do a rotary (as long as they have half a brain). ~$150 USD depending on how far off your stuff is.



Rotors end up being the same weight and spin balanced individually. Eshaft checked individually then front and rear counterweights are added with nuts and washers then that assy is done. Clutch and pp are also added to the mix.


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