I havent done too many rebuilds where I have to replace the pistons with another set of OEM and Im having a friend press the pins off out and back in..is it absolutely necessary to heat up the rod when installing or will it damage anything or cause any down the road damage if the pin is just pressed in with no heat?

 

i think you will seriously damage the rod, pin and piston if you dont heat the small end of the rod up.

 

If you dont heat it up you will kill it