Boom & bucket are 16mm & the stick is either 18 or 20mm.. a bit bigger than 5/8.
I use Esso Hydraul 50 (comparable to a 10W hyd oil).
I started out with an ATF in my home made post pounder and I had trouble with foaming (likely b/c of the high rate of discharge), so I switched to the Hydraul 50 & it cured that problem! Not sure how well it might work with this application?
After running a 5amp charge, there is a wee bit of foaming in the tank, that's usually after ripping, maxing out the pressure relief for the entire charge!
Probably your pump rpm could be considerably lower (25%) than mine, which is why the hyd speed is notably slower. You could go to 4s lipo @16.8v and then limit the EPA %'s in the gear switch & mixes to get pump rpm up to 4000. Also limit the EPA in the swing & track motors if they're not rated for that high of voltage & to keep them at a favorable operating speed.
I only know what I have used & your hyd system is quite similar to mine in almost every way.
Cheers
