I am trying to disassemble my S40 engine that was run without oil by the PO.

The wrist pin is “Frozen” in the piston. The bearing contact on the rod and pin move somewhat. Not the normal smooth movement but they move. Both spring clips are out of the piston and it will not move. I’ve soaked with penetrating oil for 2 days. I tried to pound it out. I tried a c-clamp and a socket. No luck. Wondering if anyone has any ideas on what to do.

I’m pretty sure once out the rod will need to be replaced but wanted to inspect before I tear the engine completely down.

Insert the threaded rod through the wrist pin.  Place the 1-1/8 socket over the rod until the socket butts against the side of the piston as shown.  Place nut on each end.  Tighten the nut on the socket end.  Hold the nut on the wrist pin side with a 9/16" socket.

Brilliant! I will try this as soon as I can get back out there.

Slick as snot...a little heat and once moving the wrist pin came right out. The small end of the rod looks okay. Will measure everything and decide. I’m 50/50 with tearing it down. It got hot enough to score the piston and cylinder, but the engine never stopped. I even tried to get it running when I got it.

Thank you Mike! So helpful to have other eyes and ideas.

Something you might do to help decide if a tear down is necessary is pull a side off the crankcase and inspect everything layin on the bottom. How much metal is there? How much of it is ferrous?

Drain the oil into a clean catch pan. This is where plastic is good.. A gallon oil container with one side cut out goes under the bike and holds more than enuff,,
Yes, ya ottsta have the lid on it..
Run a magnet thru..
Dissect the oil filter, dont pollute it with anything gettin into it,
Of course holding the crank at TDC and messing with the rod would tell ya something,,

Might wanna rinse the bottom of the crankcase and get everything out,, this is where I like diesel,,
Ya might even need to go so far as pull both sides off, and set a catch down and rinse everything into that.

What dont stick to a magnet might need filtered thru a paint filtered funnel, or cheesecloth, coffee filter,, piece of old tee shirt,, heck,, ya gotta study whats in there somehow..

Some bits are normal wear.. so,, just seeing signs on extremely fine bits of aluminum or enough ferrous stuff to put a beard on a good magnet isnt necessarily reason for panic.

How much and how big matters,,

Is it too big to carefully clean it up?
A low spot wont hurt anythihg, as long as it doent bleed oil pressure off..
BUT,, surrounding a low spot,, there is a high spot,, Getting a wrist pin to fit with the rod keeping even tolerances along that width is what its about,,
Splitting the case seems Very intimidating to me,, but siezing a wrist pin might not be a load of fun either..

Buddy O mine was working for Rowan drilling in Louisiana,, well,, we both were,, His dad was a big time diesel mechanic in Odessa Texas,, and Paul knew his way around one..
They had a BIG engine that someone tore down and never put back together.. and by big, I mean a catwalk down the length of it,, 6 cylinder thing, about ten feet long and eight feet tall,, best I remember from over 40 years ago..
Anyway,, Paul started hunting parts when he wasnt busy with other things,, and dragged everything up in a pile,, and the crank had a divot in it,, which had some high spots around it.. He used a file on that,, and the bought him gaskets and some minor stuff,, he put it together and it ran,,

Anyway,, point is,, a visible boo boo,, while not desirable,, may not be a problem at all,,
Your skill level and the percentage of the surface it affects may be all that matters.

You can replace the wrist pin easy enuff,,

A carefully built slot in it to engage the burr, rotate the pin?
Gotte decide which way the metal Needs to go,, and work it towards where it came from, Then a diamond bit on a dremel, keep water on it,
SLOW, using whatever ya have to to see it well,, Hobby Lobby has the eyeball cheater hoods with 2 magnifying lenses and a Loupe that rotates down,, More expensive than Harbor Freight, but better, too..

Harbor Freight has outdoor , rain proof work lite,, 250 watt halogen, cheap.

Take yer time,,
that wrist in can possibly be The tool that helps save ya from crackin the engine open,

I was able to clean up that wrist pin bore in the rod shown above.  I used a ball hone and as I recall the bore remained within the specs outlined in the manual.  Here's what it looked like after honing.