How do I tell if my 340 is internally balanced?

pt70 said

I believe replacement pistons have the same weight as the original pistons. Oversized pistons also have the same weight as the original standard sized pistons. ------- Stroker/lightweight/racing pistons are another ballgame.

The photo shows a 1/2'' hole in the last counterweight and a 1/8'' hole in another. I've never seen a factory original crankshaft with anything other than 1'' holes drilled in the counterweights.

Click to expand...

Replacement pistons same as originals? Yes. Oversized same as standard sized? No. (I used to think that too...)

The '1/8" hole' may be a spot. It makes .00001% sense to put such a small hole on the 3rd counterweight for balance purposes. Here is why: As the you move to counterweights closer to the #3 main bearing, the effect on primary balance gets proportionately less as the distance from the #3 main gets less. In other words, that counterweight with the 'spot' is only about a 1/3 as far from the #3 main as the front counterweight. So you would have to take about 3 grams off that counterweight to have the same effect as taking 1 gram off the front counterweight. (And the same applies to the rear half of the crank...) So drilling a tiny hole there for balance work really makes no sense; certainly not for any significant change in piston weights, for example.

IDK on the different holes sizes that may have been drilled in factory cast cranks.