Hydraulic Rams

[Jerf123]

Seen a thread kinda like mine, Didn't know if to ask there or start another. I don't want to be rude and get every thing off topic. If you machine a Hydraulic ram with a cylinder id of .375 and a one piece rod with piston at bottom, piston od of .375. Do you need a seal on the piston? or will air pass by but oil will not ?

And at the crown can you press in a brass bushing with a rod diameter of .125, brass bushing id of .125 also will it seal or have to insert a o ring into the bushing id?