easy balancing Q

balanced 360 short block. If I drill some notches in the pistons thereby lightening em is it now under balanced or over balanced? (I understand that over is OK (within reason). With alum weighing 2.7 grams per CC & the notches at an 18 deg angle & .030" to .050" deep it wouldn't be alot & I for sure ain't got the math skills to nail it dead on for grams but I am curious. Thank you for your time.

This is the way I look at it, you weigh up a bob weight, get you number then add a % of over balance and then balance the crankshaft to that number. So in my view you are removing from the bobweight and adding over balance to the crankshaft. You didn't say what kind of components are being used here so I will use 2300gr ballpark for a typical 360 and you will remove 2gr of material per so 4/2300= .0017 or less than 2 tenths of 1%. cut away

You could change the balance by that much by using stp in the engine. I wouldn't be worried about it in a street engine.

Why are you drilling aluminum? Stress risers=cracking is significant issue with aluminum. S/F....Ken M

Ken what is going on is I need more P/V clearance so I had to do it. My crank man gave me a (gram) # & I filled the notches with clay then dropped one of em into a burette & noted the CC rise then that # times 2.7 to get grams & as he said I am way under the limit but someone just mentioned that overbalancing is better than under so this is more of a curiosity question than an actual dilemma, that if I lighten a balanced assy (like I did) am I over or under balanceing...

you are moving it slightly over...depending on where you began at.

Your crank will be overbalanced, but remember you only add 1/2 the piston weight anyway so not by much.

Notch away, very insignificant effect on balance.

There's oil flying around changing what is perceived as balance anyway, especially at the rear of the motor in some cases when you accelerate.

That is what I needed to know & yes the recip weight is halved. Thank you!

Cut away. Among all this talk of the "balancing formula" remember that this is empirically (experience)based and not derived from the geometry of the engine, etc.

R.

Hello Dog, its been awhile. All done (& deburred). EDIT My crank man gave me (2) (gram) #'s, one that is getting close to problematic & one that is definitely too much (I got em wrote down somewhere) but he said valve notching wont even get me close to it & he was right I wasn't even close, I was just curious if it was (now) "under" or "over".