Advanced Engine Balancing
 

Has anyone on here balanced their engine to account for the weight of the oil held inside the rotors while the engine is running? Currious as to what the results where and what method was used to determine the amount of oil to compensate for.

Looking at the Mazda guidelines on balancing, the weight of the rotors, and the weight of the seals and stuff... the normal balancing procedure *does* account for the weight of the oil inside the rotors.

Where can I find those guidlines at? I'm going to be ballancing this thing myself and it is my first time doing a rotary.

Thanks,
Ken

I've always wondered about that...
All the pics I seen of dynamic balancing does NOT have oil in the rotors.
If we're talking a matter of fractions of a gram, then having a few drops of oil can throw off the whole thing!?!!?

I think all this extra charges for dynamic balancing is a waste of money... :D


-Ted

http://www.mazdamotorsports.com/weba...ject=balancing

The discrepancy between the dummy weight and that of the rotor makes me think that they include oil in there too; no way springs, seals, etc account for 554 grams.

If someone were to come up with a setup for balancing the rotors themselves, I'd b e interested... looking at starting experiments in carving weight off of the things, and I'm not so sure RB or whoever would want to deal with balancing home-lightened stuff. ;)

Oh, sounded like you had something more detailed than that, I already have that site printed out and sitting in my build book.

Basically what I was going to do is measure the displacement of a dry rotor with all it's parts put a junk rotor on my balancing mandrel with a piece of sheet metal against the gear side with a junk oil seal in place to simulate the side housing with oil return. The plate would have a hole in the center the same diameter as the oil seal track mark found on the side housing and temporarily afixed to the side of the rotor. I would then chuck the mandrel in a lathe, then spray hot wax inside it at the same distance and angle as the jets in the eshaft. Once I'm sure it won't hold any more wax I'll turn off the sprayer and just let it spin until cool. I will probably have to keep the rotor heated to compensate for wax cooling.

Once it's cool I'll measure the displacement again of the rotor and how many CCs of wax it is holding. After that I'll just weight out the CCs of oil to compensate for when I make my bob weights and HOPEFULLY I'll have the engine ballanced to within a few grams of how it would be inside a running engine.

So is that rotaring assembly sitting in a dummy engine core?
Most of the dynamic balancing pics I've seen just shows the rotating assembly spinning some some custom machine sans engine housings.



-Ted

Why would I need a dummy short block?

I wondered about balancing during a recent build also...

I thought as well....when they're spinning the rotating assembly, how does bearings/eshaft get oiled?

There's lots of pics of it in motion, but to me I'd think the bearings would get chewed after spinning them dry on a lathe/balancing machine.

Why would you use good bearings while balancing? Just do it before their replaced.

I think they balance the rotors and match their weight individually and then use a weight equivalent to the rotors, seals, and oil an the e-shaft to dynamically balance the counter weights to the rotor weights.

The question is not how to balance and engine, the question is how much weight in oil is needed to compensate.

You can't compensate for oil being inside as the oil is always moving around. If your engine changes rpms, the amount of oil inside it will alter it's location too. It gets sprayed in but it literally drains out the sides of the rotors into the center housing. They aren't balanced with oil in mind. They are balanced dry. You also don't worry about bearing lubrication during the balancing procedure as you aren't using them. You are basically using what accounts to nothing more than a lathe. The lathe ends are a point that insert in the ends of the e-shaft on the centerline. The balancing works like a tire balancer in principle.

You're dead right. According to a good friend of mine (RIP) who worked with Mazda in the 70's they definately allow for oil in the rotors.

I have always used the same person for balancing and never had a problem (up to 11,000rpm). He will NOT tell ANYONE the weight for oil allowance and with good reason, it appears very few people know it.

I recall you asking this same question a year or so ago. Im guessing your balancing guy answered your questions? Hopefully we use the same guy! ;)

i think the oil is a variable which can change so many times during a run that to finger a exact number will be a great undertaking......it is like the riddle of the bridge whic can only hold 100lbs and you have to get accross, with 3 grapefruits, but you weigh 90lbs, the gapefruits weigh 10lbs each.....which means if you carry all 3 you and the fruit will break the bridge, so how can you make your crossing?

simple just juggle the fruit.....lol
the moral of m story? hmmmmmmmm fill the rotor to max and weigh that amount then make a good guess of how much half full is and use that figure....(JUGGLE)
my reasoning...simple even if the heaviest oil weight is used, the rotor is spinning thus in theory only half full due to cetripital forces...even if a full quantity is sent all the time......I dont know if this make s sense even to me...LOL

Well because of rotor design and centrifugal force there will always be a specific minimum amount of oil in the rotors. When oil pressure goes up more volume of oil should make its way out of the jets and so there may be the possability that more oil accumulates but since RPMs will also increase it will force a portion of that oil out faster. Mazda calls for the parts to be balanced within 50 grams of each other which is a lot of weight. I think if I atleast account for the minimum amount of oil in the rotors at all times and get them balanced within like 5 or 10 grams then I would have made enough of an improvement to justify the costs. I'm using an RX8 eshaft though with S4 counterweights so I might have to rebalance anyways, I'm not sure if the balance of the eshafts are actually different or not, people have told me stuff based on assumption but assumption is the mother of all fuckups.

The RX8 shaft is lighter so unless you use RX8 rotors and weights you will need to rebalance. As for how, Kenku gave you the link...

The weight given by Kenku for a 13b rotor is pretty much what a dry rotor weighs.

Well if you want to know, why not find the weight that is in there now and where it is placed, then take it to someone else who doesn't know the "oil correction weight" have them balance it, and split the difference. There's your weight correction for oil.

- Steiner

So when you make the rotors the same weight how do you know where to take the weight out of it, or is just there total weight matter. And in that case would you take out the weight closest to the center bore fo teh rotor?

Next do you just bolt cirular weights in place of the rotors And balance the counter weights/flywheel?

Kenichi Yamamoto (author of 'Rotary Engine' by the Mazda tech. department) specifically mentions the need to balance the rotors using their full assembly weight - including all the seals and springs (apex, corner, side) and oil inside the rotor.

as i sadi maybe if you pour the expected amount of oil into a container and weigh it you can rough estimate the needed weigth...........I just had a thought though would you need to take into account the centrifugal forces which may add weight to the oil being flung out? and if so what would that number be? maybe 8.1? GRAVITY? i ma not sure

If that's the case, don't forget the oil control o-rings and springs!

So, who does a good job at balancing an engine and what is the cost?