Are these pressed in pins or floating pins?  Are there little lock clips in the piston to hold the pin in place or not? 

Most likely, the thing was either assembled that way or there is some burned oil coked up causing the stiffness.  If it gets worse, its a good way to bend/break a rod.  At the very least, disassemble, clean and reassemble.

OK, there's really not a redneck way to "fix" this. I am a victim, as are about 12 other people on this site right now, of bad assembly and cutting some corners. Mine, I blame myself totally. I mandated improper tolerances for the application, and assembled myself accordingly, taking "close enough" as "good enough". Learned a $4k lesson on Moo. Never Again.

Do it right ONCE and the first time. Might cost up front, but take the time to measure, measure, measure while assembling and if sumpin ain't right, get it to a shop. You'll thank me later when next year, or the following year, or 5 years down the road, your boats still running and a lot aren't. 

Ray