'63 75hp "Sloppy" Pistons (Ongoing Rebuild)

[yorab]

Well, I've taken the crankcase off of the powerhead. I'm following the Seloc and Factory Service Manual to the letter. Between the manuals and my prior automotive repair experience, I think I'm doing okay. However, this is my first complete engine rebuild, auto or marine. The engine is in relatively good shape. I am led to believe that it has been rebuilt before.
I had no 'stuck' fasteners (a problem that I encounter with EVERY auto repair that I handle).

Also, the high temp paint on the inside of the intake manifold looks like it was applied 3 days ago.

The cylinder walls are not scored and have a reflective appearance. There is only very superficial marks on the cylinder walls.

The piston rings seem to be seated well and are still shiny in appearance. (I will learn more about them when I extract the pistons.)

The bearing surfaces on the crankcase cover are very smooth and mirror-like.

However, when I grab the pistons in the cylinder bores, I can move them back and forth perpendicular to their intended path of motion. I can't quantify the exact amount of slop just by feeling, but I would imagine that it is probably about 1/64". Also, the connecting rods have some slop in them when I tilt the rods perpendicular to their intended path of motion (in other words, the rods and caps tilt toward the ends of the crankshaft).

I hope that my descriptions make some sense. If not, I'll try to re-explain. Should there be any slop in these components? I will hold off on the disassembly until I find out more about this.
Thanks

 

[yorab]

Re: '63 75hp "Sloppy" Pistons (Ongoing Rebuild)

Well, I have taken out the pistons. 3 of the 4 are badly scored and galled. I will replace at least 3, maybe all four depending on price. Still not sure why there was slop while the pistons were in the cylinder bores.
I found one of the labyrinth seals broken. My manuals don't mention much about these. Can I replace one or should I replace all three? Do you install these seals like a piston ring? In other words, do you simply open up the ring then place it around the crank?

 

[Evinrude Boater]

Re: '63 75hp "Sloppy" Pistons (Ongoing Rebuild)

I would think the piston clearance is normal. The aluminum pistons and steel bore would expand at different rates. As well, the bore can be tapered and out of round and the piston clearance allows for these deviations.I replaced a trail bike piston and it was so tight that it would seize when it heated up.
I would replace all seals while the engine is apart.

 

[F_R]

Re: '63 75hp "Sloppy" Pistons (Ongoing Rebuild)

The pistons are normally surprisingly sloppy at the head end. The clearance is measured at the skirt and is much tighter. Yes, use a regular ring expander on the crankshaft seals.