Engine balancing

[tparker]

I don't recall how much I was charged for it but it was around 200-300. It had the whole motor done. But there wasn't any discussion about that number changing because it was harder, more labor intensive, or needed more weight. As far as I know it didn't need any balancing and they kept the 200 or so bucks for no work. LOL. Not sure if this all changes if you take it in just for balancing though.

[7E-Bodies]

My shop had the price sewn in for balancing. My NM 440 needed a .020. Small money I gladly spend as I hope this is the last time I see the lower end apart, especially in pieces in the middle of a huge oil scatter if you catch the drift.

[1 Wild R/T]

Why would you choose new pistons that are heavier than the originals?????
Loosing weight is how you make an engine rev quickly & at the same time it's easier on parts because your throwing less weight around....

[1972V21Cuda]

Why would you choose new pistons that are heavier than the originals?????
Loosing weight is how you make an engine rev quickly & at the same time it's easier on parts because your throwing less weight around....

I was thinking the same thing. Some of the older aftermarket forged pistons were heavy. But, nowadays, most forged pistons are lighter than the factory stuff.

[IRON MAN]

The machine shop I took my '68 AMX 390 engine rotating assembly for balancing required everything from the harmonic damper to the fly wheel/flex plate. He discovered one of the new pistons was 6 grams heavier than the lightest piston. He said, that is unacceptable. We both contacted the piston manufacturer and they over-night-ed a new piston. When I picked up the rotating assembly, the owner said it is balanced within 1 gram  from the harmonic damper to the flexplate.   

[jamesroney]

The machine shop I took my '68 AMX 390 engine rotating assembly for balancing required everything from the harmonic damper to the fly wheel/flex plate. He discovered one of the new pistons was 6 grams heavier than the lightest piston. He said, that is unacceptable. We both contacted the piston manufacturer and they over-night-ed a new piston. When I picked up the rotating assembly, the owner said it is balanced within 1 gram  from the harmonic damper to the flexplate.   

If your engine balancer requires the clutch, flywheel, damper, pistons, rods, crankshaft and bearings...then you NEED to very closely supervise them, and specify how you want your engine balanced.

The fastest way to balance the rotating assembly is to calculate a bobweight, add the mass to the rod journals, add the damper, flywheel, and clutch...and spin it up.  Then you an add weight to the clutch to bring it to spec.  This is the absolute WRONG way to balance an engine, unless you are a 1/4 mile jockey and you run your engines for 10 seconds at a time.

The correct way to balance an engine is to balance the components individually, against a calibrated standard.  First you match and balance the components...then you add and subtract metal to balance the crankshaft.  Then you add the damper flywheel and balance those. 

You didn't say whether your 340 was a forged or cast crank.  If it's a forged crank 340...those are internally balanced...and you should NEVER see an external weight added to the clutch, flywheel, or damper.  Those pieces are all neutral balanced, and should never need weights.  If they do need weights, then they should be replaced.

I have pulled apart numerous engines that were balanced as a matched set.  When the clutch needed replacement, the engine needed to be re-balanced.

External balance engines are a little different...because mounting location and rotation angle becomes important.  For those, you do need to balance them as an assembly...but ONLY after first balancing the crank individually with a calibrated flywheel.

If you are going to race your MOPAR, and rebuild the engine every season...then the balance strategy is completely different than the person that is building his engine to last for years.  Many Race shops don't think this way.  All OEM manufacturers think this way.

To use the tire and wheel analogy...imagine that you balanced your tires by WELDING a weight to the back of the wheel...then very carefully marked where to mount the tire on the rim.  As long as you use the same tire/wheel combination...it works just fine.  but if you ever replace your tires...you would then need to throw away your rims.

My last balancer told me not to worry about longevity...because I could always just bring the parts back in and he would re-balance them for me.  He didn't see that as a problem...

[Chryco Psycho]

The Only situation where I can see choosing a heavier piston is if you were removing a weaker piston such as a Hyperutectic & replacing them with a forged piston which could be heavier or taller adding weight with compression , otherwise I agree why ever go to a heavier piston !