Manual E shafts have the pilot bearing and oil seal installed to support the input shaft of the transmission. Automatic E shafts are bored for the outside diameter of the pilot bearing, but none is installed. The balance of both shafts is the same.

 

If any of your weight sets actually came from the same engine, just check for a matching number on both weights. Usually a big 4 digit number stamped in deep. If you don't have such a set, ask Racing Beat or Mazdatrix if they will balance up a set from what you have. They will need the rotors you will use in your engine.

Then you will have a matched rotating assembly.

 

There are permutations of situations that can be worked out. Suppose you have both weights and a shaft from one engine with matching numbers but one rotor is not serviceable.  The weights are not used to balance the rotors in the way you would think. The weights are there to take out a rocking couple. That is an imbalance caused by the fact that the rotors are not turning in the same plane but are displaced along the shaft and that causes the ends of the shaft to try to spin in a small circle. Kind of a wiggle. So, the weights just take out that wiggle.

 

The rotors weigh about 10 pounds and are very close together weight wise, and in 90% of the cases you could grab any rotor from the same year engine and run it for years with no problems at all. The rotors are marked when new with a paint dot that shows its weight class. I think there are 5 such colors and Mazda allows a 2 color range of colors.

So if you have a weight class 3 rotor you could assemble that with a class 2 or a  4 and have an as new balance job from the factory.

 

So close is good enough. But for racing I built a balance beam scale out of a 2X4 and some dry wall screws that can detect a penny move 2 inches on the end of the beam. Way better than close enough.

 

So the known good balance rotor from the same engine as the same numbered weights goes on one end of the scale and a good unknown rotor on the other. I have a good supply of rotors so it works for me.

You keep trying until you get the same weight or one that is heavy.

Then lighten the heavy rotor to match the known rotor and assemble.

 

Or throw the whole thing in a box and ship to one of the above shops.

You could send just the shaft and weights and ask for new rotors in your balanced rotating assembly.

 

I have disassembled engines with different year rotors, wrong year counter weights and front an rear rotors reversed (in 12-As).

The balance is so close that most people cannot feel the worst case balance job in a rotary.

 

Call Racing Beat or Mazdatrix before shipping anything and follow their instructions exactly.  Both good people. 

 

You can download the Racing Beat catalog for free and it is full of such information.

 

Lynn E. Hanover

 

1. How do you tell an automatic vs manual eccentric shaft?  Is there a
difference?  What is the difference?


2. Suppose I have several eccentric shafts, front counter weights and
rear counter weights of unknown origins how do I go about selecting a
workable set?  What parameters do I use for the selection of each component?

Thanks for any replies.

Jim Brewer
Albemarle, NC