Hi all. Overhauling subject engine. This is time sensitive as I want to start re-assembly in the next few days when I get the block and heads back from machine shop.

Decided to re-use pistons. Look terrific. Micrometer the pistons and telescope gauged the bores (repeatedly), and both check out and the clearance is actually still in "ideal" range according to Specs sheet. Got new rings too. As I am keeping old pistons, con rods still attached. No play between the piston pins and connecting rods, nor the pins and the pistons, so that'* good too. Connecting rods bearing seats/caps NOT out-of-round.

The piston pins are "FULL-FLOATING", which is defined as: "FULL-FLOATING pins are not secured to either the piston or the connecting rod.".

5 of the 6 piston pins fully float as described. The pins are able to slide right and left a fraction of an inch (app. 1/16"), and what keeps them from coming out are snap rings in the end bosses on either end of the pins. Furthermore, the connecting rods can slide left and right on pins, a little more distance than the pins can move left/right "about 1/8" of lateral movement across the pins). So, the pin floats in the piston bores, and the conn rods float on the pins.

Here'* my issue: on Piston #1, the connecting rod seems to be "fused" to the pin. So, when the connecting rod is moved in an arc motion, the pin must rotate with it. The connecting rod with fused pin still moves left and right, because the pin itself is floating in the piston. The end result is that if you hold pistons #2 through #6 facing the floor with the connecting rod caps facing up, you can then move the connecting rods right and left, say 1/8" (the pin slides left or right until it hits the snap ring and the then the rod slides a little further along the shaft of the pin until it hits the inner piston housing). HOWEVER, on piston #1, because the connecting rod is "fused" to the pin, holding the piston as described and moving the connecting rod left and right only results in about half as much (1/16") lateral travel, because the pin will float left or right in the piston until it hits the snap ring keeping it in, but the connecting rod will not travel any further along the pin. Also as a result, unlike pistons #2 - #6, the connecting rod cannot travel far enough to the right or left to hit the piston inner housing.

The end result if that I have discovered 5 Full-Floating piston pins, and 1 Semi-Floating piston pin in this engine. Semi-floating is defined as: "SEMIFLOATING pins are secured in the middle to the connecting rod (fig. 4-15). The ends of the pin are free to move in the piston pin bearings in the bosses."

Here'* the thing: this car was driving fine with this reality, for many miles. No knocks or anything, no extra wear on that cylinder, piston in as good of shape as any other piston. Seems to me that the location of the connecting rod on the crank, and the fact that the cylinder bore prevents the piston from moving horizontally during its up and down motion, means the "floating" of pins appears optional, other than the couple of thou the crank might move forward and backward in the mains during operation. In fact, there is a type of piston pin called "Stationary", which is defined as "The STATIONARY pin is secured to the piston at the bosses, and the connecting rod oscillates on the pin." That is, the pin is "frozen" from moving left or right or rotating, and the connecting rod rotates around the fixed pin.

It might be possible this engine was overhauled by the previous owner and the machine shop installed piston #1 using a Semi-Floating pin, whereas all the other pins are Full-Floating, but this is highly doubtful. I have no reason to believe this to be the case, rather it appears that for some reason, the pin on piston #1 is seized on the connecting rod or to use a neutral word, fixed to it. However, there is no discernible play in this assembly, just as with the other piston/rod combos.

HERE'* MY QUESTION: based on the foregoing information, should I pay the machine shop to put a new Fully-Floating pin and connecting rod bushing on this piston/rod assembly? Or should I reinstall it in the engine along with the other 5 assemblies, because I have confirmed:

1. Like the other 5 assembiles, there is absolutely no rod to pin or pin to piston wear/clearance problem;
2. The car probably did its last several dozen thousands of miles with this situation; and
3. There is such a thing as a "Semi-Floating" piston pin (the end result I have described for piston #1), even though this engine seems to use the fully-floating assembly type.

I am trying to keep costs down. Also, I don't want my parts to be a the machine shop an extra 2 weeks because they have to bring in a new pin. Maybe you have a different opinion, but I cannot see why the 1/16" of lateral float this connecting rod has is any more risky than the 1/8" the other fully floating ones have (I think the only lateral motion on the connecting rod during the stroke would be equivalent to the end play on the crank and/or some minor flex in the crank at high RPM; just a couple of thousands at most).

I could try laying the piston on its side, holding the end of the connecting rod or putting a block under it for support, and them giving the rod a whack with a rubber mallet just below where it joins the pin to try to "free up" the rod-to-pin meeting point, to see if it will go from Semi-floating to Fully-floating again. Would another option be to do this, and if it fails then, and only then have the machine shop do the re and re of the pin on that assembly? Or, should I just stop fretting and reinstall the damn thing.

Thoughts? I appreciate it.

Punch the pin out and put it back in to see what happens.