1983 35hp siezed after sitting for 5 years.

[starcraftkid]

The measurements are correct, I've got four sets of micrometers, and three pair of Mitutoyo and Starrett digital calipers here, I've got a Starrett 3089 bore taper gauge, and two sets of telescoping type gauges as well.
There is no mistake, the pistons are larger than the whole, if they weren't, I wouldn't have ever made this post, it would be a non issue if they came out and were just fine or damaged in a normal way where I just tossed them in the bucket with the rest of the scrap.

If all this made sense it would have been stuck on the shelf and forgotten about or on its way to being finished by now.
The bore measures 3.00" The bore is round and square.
The pistons measure 2.96 just behind the ring lands, they jump up to 2.98" near the pin, then they jump up to 3.014" at 1.377" from the bottom of the skirt. Both pistons are identical.
No, they will not fit back into the bore, if I remove the rings, and turn the pistons over, each piston will drop freely into the bore up to the point where the skirt expands.
If I hadn't taken them out myself I'd never believe they came out of there. When I removed them, the whole block, with both pistons in it just came out of the spray wash cabinet. The spray washer is set at 165°F.
The parts are too hot to touch when they come out. After soaking the block in Evaporust to clean up the cylinders I ran it through the washer to heat it up. Then I was able to tap out the pistons using a block of wood and a mallet. The top piston moved easier than the lower but neither was severely stuck, but it was when it was cold. I really was expecting to see severe rust pitting but the cylinders are spot clean, no sign of any pitting or rust, no scoring, the same with the pistons. With as tight at the pistons were I also would have figured they would have been scratched up but there's not so much as a mark on them.
I can't imagine anyone thinking that stuffing oversized pistons into a too small bore would ever work, the only way it could be done is by temperature difference, but that would likely have locked it up the instant both parts equalized in temperature. Considering this motor really looked untouched I doubt that's the case.

As a test, I heated the pistons back up in the spray washer, at 167°F, the piston measured 3.023" growing .009". (no rings, piston pin, or rod attached).
I did the same with one of the other used pistons and those only grow .004" when warm.
The pistons from this motor are much heavier than the used sets I have here. The difference several ounces or so. Enough that its blatantly noticeable in hand.
The simple fact that the used pistons, which I have here from another motor I took apart a few years ago, will drop right in and fit fine, the issue here is with the pistons. The used pistons are 2.96 to 2.97 at the bottom of the skirt area. With the rings off, they move freely up and down in the bore on this motor as they should. I have both a set of brand new OMC std pistons here and a set of Wiseco pistons for this if I were going to rebuild it and both fit just fine into the stock 3" bore.
I have no doubt that at room temp, the pistons I took out would not be able to be reinstalled without major force and severe damage, but the big question is what on earth happened to these and how did they get this way or how did they manage to gain size after coming out of the block and cooling down.

 

[reelfishin]

The only thing that comes to mind here is that years ago I had an older 40hp twin that had gone into the water at wide open throttle.
The motor was recovered the same day and I was told they flushed it out with raw fuel and then filled it with mineral spirits in hopes to un-seize it.
I ended up with it after they gave up.
It had been a week since it went swimming when I got it from a local scrap collector. When I tore down the motor for parts the pistons were both stuck, but there was minimal rust. After tearing it down to just the block and pistons I ended up heating the block up with a propane torch and cooling the pistons with oil while pressing them out. The worst part is that the motor was super clean, likely hardly used at all. After sorting through all the parts to see what's good and what's bad I found that the pistons were badly out of round, as well as now measuring larger than the bore they came out of.
I still have them somewhere, but at the time I took them over to a local machine shop that did outboards and the guy said that aluminum cools faster than the iron bore in the block, so if the block is hot, and a rush or water flooded the motor, in which case would into the crankcase first, it likely hydraulically locked the motor on the downstroke, sort of freexing the back of the pistons at their now expanded shape being both expanded by heat and the hydraulic effect of the water. The block cools down, the pistons have already taken a set or warped and its locked up for good.
My first thought was great, two new pistons and its good to go, but closer inspection showed a horizontal crack about 1/4" long in the lower cylinder bore about 1/2" from the bottom of travel.

The part that got me was that I knew it was a running motor, it had to be if it fell in the water running, and I knew I had just knocked out both pistons myself. The pistons were .007 and .011" larger than the ID of the cylinders themselves. I've never seen it again but I don't generally get many motors that have been sunk while running. I parted the motor out, the block and pistons are still around somewhere but neither were good for anything other than proving my sanity.

After reading through these two pages one thing that sticks out is the fact that the remaining second ring now has no gap. Rings are made from cast iron, so it makes me think that motor either went through some sort of thermal shock as well as maybe being hydro locked with water at some point. The rings being ill fitted tell me someone was in there before but factory screw ups do happen. Having no gap or a negative gap usually means the ring breaks when installed if the end tangs didn't somehow overlap but compression would have most definitely suffered.
I did have a near new 20hp back in the 80's that had low compression on the top cylinder. It was less than two years old when I got it and it had 70/120 psi on the two cylinders. When I opened it up the top piston was missing the second ring altogether. I put new rings in it and still run that motor today. When I checked the three remaining rings two of the original rings had no gap, the third had over .020". Finding screwed up ring gaps, especially in motors that failed is not surprising. Whether or not it was a cause or effect is a big question but matters little in the end.