Second guessing NOT balancing engine
 

I've completed the bottom end of my 911 engine build. I'm getting ready to put the top end together. I was recently reminded about balancing of the rotating assembly. I really would hate to tear the engine back down to go through the full balance. But whenever I discussed doing this when I had my crank at the shop, they said that boxer engines are inherently balanced and not worth it balancing (can't recall if he was just referring to the crank or not).

The engine is a 2.4L. Stock crank and rods with JE pistons. The engine will not be used for track/race conditions but it'll be revved from timed to time. What do you think? Looking back I should've had it balanced. My question is, is it worth tearing down the bottom end to do so?

Thanks,
Kelly

I was told that the cranks are nearly perfect from Porsche. But to check the rods, especially from end to end. Porsche groups their rods according to weight. IIRC their tolerance is 9 gms. I checked the rods in my 3,0 and they were all within 1 gm. Less than a gram end to end. When I get my pistons, I will measure and adjust them as well.

I'm undecided on my flywheel and clutch as to getting them checked. A machinist friend of mine has a balancing setup, but lives in San Diego.

Crankshafts with evenly spaced throws are inherently balanced in a rotational manner. Boxer engines are also inherently balanced from a reciprocating standpoint (although there are unbalanced moments due to the offset of the cylinder banks). The only balancing that is done is to correct for small variations in weight between parts that are made in the real, not theoretical, world.

I was in your boat in the past and did not either.

Lost sleep over it many of times. Seemed to rev buttery smooth all the way to redline and hasn't let go years after rebuilding.

The natural "balanced" effect of a 6 cylinder helps I'd imagine.

just finished my 2.7, no balance, runs awsome. Smooth and quick. You should be fine;).