New pistons in 68 318

Confusedcuda said

Hello all, wanting to put new pistons in a 68 318. I noticed the KB 167 pistons weight 526g and the stock pistons weight 592g. Does this mean I need to have some material removed off the crank for balancing once I install the new pistons? What does this apprx. cost at a machine shop thanks.

Click to expand...

Short answer...yes, you should get it balanced.

Long answer...the pistons are not the only difference. The wrist pins for KB pistons will be around 132g and factory was around 154g. So, now you are looking at 66g (piston difference) + 22g (pin difference), for a total of 88g...or 0.194 lbs off each piston/pin. Multiply that by 8 and you are essentially taking 1.55 lbs off the reciprocating mass. That's quite a bit!

Balancing runs around $150-300 IF they don't have to add weight to the crank...which should not be needed in your case. Since you're looking at balancing now, I'd strongly urge you to NOT reuse the old rods. Scat makes some nice I-beams (~$350/set) for around the same as you'll spend to rebuild your old rods. The added bonus, large rod bolts and even more weight savings (595g vs. 726g). Factoring in the added weight savings on the rods (131g x 8) and you will have taken a total of 1752g (3.86 POUNDS!!!) off the reciprocating and rotating mass of your engine. It probably won't show on any dyno pulls...but it will rev a LOT faster!