To Balance or Not to Balance...
 

Just assembled my 1993 13b block and now I am at a fork in the road. I have matching rotors and front counterweight, but rear counter weight is off a 1994 auto. Traded flywheel for counter weight at 90k miles. Ran car 15k miles until oil control ring broke. Noticed slight main bearing wear(mostly at the bottom where babbitt coating was gone) and eshaft journal wear during rebuild. New rx8 eccentric shaft and proper main bearings installed.

Should I disassemble the block and get the rotating assembly balanced, get a new Mazda flywheel, or run it like it is? This will be a babied street car that I want to last another 100k.
Thanks in advance.

8k rpm redline? run it as-is, especially if the block is together.

How did an oil control ring break? I've never seen one of those fail.

Sorry, I said it wrong. An oil control seal had become brittle and was cracked in multiple places. Also compression was on the low side.
Thanks for the input.

Ah, that sucks. I take it the rings had much more than 15k miles on them.

Babied car?

Yeah, the rings had over 100k miles on them.

Yeah, I don't make enough money to rebuild this thing ever again! :lol:

Car had 90k, then changed clutch, drove an additional 15k. Now car has ~105k miles and being rebuilt.

Balancing a rotating assembly is only for those that regularly want to/need to rev the engine way out past 8k rpms. For example NA rotaries for racing, properly ported, make decent power all the way out to 10k rpms. In this case balencing is a good idea ;) As Rich mentioned below 8k, don't worry about it.

Regards,
crispy

Thanks guys, just wanted to make sure this would be acceptable before I go too far.

What about for an auto-x application . where I would like to raise the rev limit to 9k . even if it doesnt make power , but jsut so I dont have to shift right before a turn rather hten bounce off the rev limiter?

I plan on using an RX8 shaft , new bearings .

Would I need it rebalanced?

I'd say it's a good idea, yes.

Its always a good idea.

Having matched rotors means nothing if they are not matched to both counterweights. There are 5 weight divisions on pre Renesis rotors A-F. What if you had all "A" weights and installed a rear counter matched to all "F"s or vise versa? You would have a rotating assembly WAY out of balance. Having all "C" weights is middle ground for all the counter weights. Also the lighter Rx8 e-shaft effect the overall balance as well. Your mix matching too many rotating parts. I recommend a balance.

Considering getting mine balanced while its apart as I'm fitting a light fly. Worth doing? B weight rotors if that makes any dif ;)

Balancing is always a plus for smoothness and better performance.

Does not compute..... :allcho:

I have never heard of counterweights having a weight class. If that is the case then we all are doing it wrong (installing the ACT or the OEM counterweight without knowing the rotor weight class in most cases.)

Thanks for the info balancing it is .

I agree with the others, not needed unless you feel like spending money, or plan to rev your motor really high :)

I'm sorry to say that most here are doing it wrong. The counterweights don't have a weight class. That's what the small balancing drill holes are for. Each factory rotating assembly is balanced to it's specific rotor weights.

I don't know the weight status of the Renesis rotors. That's why I said it like that.

If your removing the manual flywheel and replacing it with an auto counterweight, try to find a used counterweight matched to rotors used between A-C. That's how you keep the balance. Mazda allows for one weight divisions + or - on rotor weights to not need balancing.

Example: You have all C rotors and damage 1. You can replace that rotor with a B or D rotor and not need balancing. Your staying within the 1 weight limit. Now if you damage both C rotors, you need to find both rotors near the C weights B or D.

The weight division thing can be confusing. I personally made a mistake on my own 91 vert rebuild back in 2005. Both my A-B rotors were damaged when the engine blew. I replaced both rotors with a matching C set thinking I was ok and within Mazda's weight guidlines. I thought that as long as both rotors were close in weight to each other was all that mattered. I was wrong as my engine vibrates. It took me years to figure out what I had done wrong. During research, I found out that "A" rotors are the heaviest and E's are the lightest. So overall my C rotors were lighter than the A-B"s that I originally had. That's why my engine vibrates.

I meant A-E. My bad!