Reply To: Engine assembly sequence

#426978

I have been struggling with getting the piston pins and pinch bolts installed in the rods. It is a push fit for the pin in the piston, but I couldn’t get the pin to turn in the rod so I could line up the notch machined in the pin that locks it to the rod with a bolt that “pinches” the pin on the rod. I tried heating the rod end and freezing the pin. By the time I got the pin in the one side of the piston, thru the rod, in the other side of the piston and tried to install the pinch bolt,  things cooled or heated up to the extent it locked the pin in the rod.

I started to do some measurements. An old motor article which has just about all the clearances for just about anything on any car in the 30’s. It listed the PA pin at 15/16″.(.9375).

I mic’d mine at .9465. I then mic’d the bore of the rod and got .945 in the 3-9 o’clock axis and .947 in the 12-6 axis. Just enough to prevent turning the pin in the rod. Evidently the pinch bolt becomes oval when released. So close but so far.

I also had some burrs on the end of the pin hole so I bought a 15/16, 320 grit flex-hone and ran it thru the pin hole about 5 strokes and checked for pin fit. After about 3 cycles I was able to get a push fit on the pin and was able to rotate it. I assembled the pin, rod and piston and was able to rotate the pin so I could get the bolt in. Tightened it up and its ready do go.