I bought some new pistons to my R5P7 to make some more compression and they are 36grams more than previous ones. I can get lighter pins (105gr vs 85gr) but still 16grams more than "stock" ones.

1. Do i need to balance rotating assembly?

If i do, should go with the 105gram pins for added safety or should i use the slightly thinner ones (85grams)?

You might be able to have a machine shop get the weight out of the pistons. If you can't then it will come out of the crank. Not sure about the light weight pins, and how strong they're for that application.

I would suggest rebalancing, and keep the pins that were in the original pistons. The cranks are super LW to begin with, so consult your balancing shop if there is enough room left to add mallory metal? Some of the cranks have such tiny counterweights, that they're entirely heavy metal with little to no space left for additional balancing weight. I actually have some cranks that have heavy metal in the bored out rod journal just to make weight. I can show pictures if you need to discuss with your balancer.

Mike

Seems like the best idea would be to use heavier pins and rebalance the assembly. Better to be on the safe on the pins althought not very common to fail.