piston pin really tight
 

I am rebuilding my 73.5 CIS 911 Targa and the OEM piston pins are not happy going into the OEM pistons. The pistons were cleaned at a machine shop and the pins are not happy trying to insert back into the pistons. Should I have to knock the pins in with some force with my plastic hammer or should they simply slide in?

You may want to check the edges of the pin bores in the pistons for burrs & check for any dirt/grit left in the pin bores from the machine shop.

Also, just in case you didn't try this already, put some oil or lube on the pins and in the pin holes to help them slid in with a little tapping with a rubber mallet.

Keep the pins in the fridge overnight...they will slide in easier.
Bob

Bob has the right idea, I heat the piston crowns with a propane torch. You only need to get the pistons hot enough to slip the pins in.

-Andy