OK, we have a 1982 ski nautique with the PCM (ford) 351w.
it is a reverse rotation engine. it ran OK but had a miss to it.. not like a noticeable dead miss but something just wasnt right.
So i check the compression and all the cylinders were between 115 and 120 except for number 7. it was 0. litterally 0.
so i assumed it wasnt the rings and i went ahead and pulled the heads off. and the exhaust valve on that cylinder had a chunk broke out of it. and the piston was a little buggered up under that valve. ( only under that valve. i assumed if that piece of valve was rattleing around in there that the piston would be buggered all over the place) it looke kinda like pre-ignition cuase it looks both pitted and looks like little bits of slag in the area that the piston is messed up.
so i took the heads to my machine shop and they took them apart and cleaned them up and called me and said they were both cracked. one crack in each head between the valves on repective combustion chambers.
so i he told me the cast numbers (d8oe i think) and i called the local ford junk yard and he just happened to have a marine engine with the same heads on it.. and he said the engine looked really fresh to him when he pulled it apart. so i got the heads...... and i went ahead and spent 15 extra dollars to get the #7 piston and rod from him since i was there and its over 30 min. ride.
so the machine shop said the new heads were in great shape and good to go.
well since i was sure about the piston and i went ahead and picked up that other one just in case i was gonna think about swapping the pistons. i assumed they were the same size cause neither had anything stamped on the top to indicate that were larger pistons.
i was just gonna take out #7 rod and piston. put my bearings in the other rod and use the other rings and put the, (new to me) piston/rod/rings in with my "old" bearings.
the hitch that i have now is that in my old piston there is a cast mark on the side of the skirt right above the wrist pin that has a 54 cast into it, and the other piston in the same place has a 65 cast into it?
what do those castings mean, and are they meaning less and can i go ahead with my plans?
My best friend is heckleing me telling me that i should just overhaul the whole thing since i have it out. but i think if it isnt broke. dont fix it. and right now if i put that "new to me " piston in. i can finish this project with a $91 gasket kit from my marine supply house that i use. and if i do an "overhaul" i'm looking at about $900 minimum. from this point forward.
the engine ran fine. didnt knock and youd be surprised at how much power it had and how well it ran with that valve broke.
So i'm just looking for opinions/advice/pointers on what to do.
i'm going to take both pistons and the bearings from they rod the the machine shop and let him look this stuff over. but i would like some other opions too.
So what do yall think.
on a side note. we are probably going to sell this boat within 2 years and buy my cousins 2001 malibu ski boat. and while i'm not trying to "screw" whoever we sell this boat to. rebuilding this engine will not make this boat "worth" anymore and i dont want to dump a lot of money into it if i can make it run fine.
so agian.. what do yall think.

 

Its a big gamble either way but you're guaranteeing an engine failure if you change the rod, bearings and rods become matched components once an engine is broken in and they should not be touched unless the motor is getting a full rebuild. Swapping the used piston onto your rod may be the better option but there's always the possibility the rod has been damaged and it may let go suddenly at some point in the future too.

 

That does make sense.
Anybody else have any input?

 

The different numbers probably indicate different mold numbers for the cast pistons, they will have other casting numbers somewhere, maybe inside.

They would most likely be fully interchangeable other than being worn into different engines. A danger could be that the replacement 65 piston has its rings a hair higher than the old 54 piston, due to tolerance variation. This would let the rings smack into the ridge near the top of the cylinder. A ridge reamer could be used to remove the ridge.

How bad is the old piston? Can it be cleaned up with files? A few dents in it might be acceptable. Just make sure that the lands aren't pinching the top ring, preventing it from freely moving in its groove. Also that the rod didn't get bent or any other obvious damage occurred.

The auto machinist probably will have the best advice, as he will be able to see the parts and hopefully have experience with frugal repairs.

 

the only obvious damage is that the piston is buggerd, and the cylinder is a little scared above where the rings stop in the cylinder wall.
the rod looks fine and i got a new rod bearing today from auto zone.
the guy there said the bearing was an original bearing made in 69.
which amazes me cause im pretty sure this is the engine that came in this boat and its an 82 model.
anyways, one thing that he and i noticed was the new bearings had a hole in them and the old bearing did not. and neither of us really knew how the old bearings got oiled with out having and oil hole in them the answer may be something dumb that i'm over looking but i'd like an answer to that none the less.

 

The old bearing probably had a 1969 engineering number stamped on it, which is what the parts man presumably assumed was a manufacturing date. This was a C9OE... number, right? Which would mean that the bearing was originally intended for the 1969 Fairlane, but used on all 351W engines for many years. There should also be a real date code on it somewhere.

The hole is to align with an "oil squirt hole" on early engines. This was a small hole drilled in the connecting rod that shot a tiny bit of oil up onto the cylinder wall at one point of the crankshaft revolution. The 1982 engine must not have these holes in the connecting rods, so no oil holes in the original upper bearing shell. But the aftermarket bearings come with the oil holes so that they will fit both early and late engines with or without oil squirt holes.

The bearings are fed pressurized oil through drilled holes in the crankshaft.

 

Be sure to have the big end of the con rod machined round for the new bearing, don't just put the bearing on and bolt it back together.

 

All right, we got it back together and got it running, it fired right up. no problems, Idles OK, revvs really good and is smoth at all RPM.
the only problem so far is that when you rev it, it revs good, but when you let off, it doesnt go back to idle very quickly. When you let off the RPM drop. but not all the way to idle, then it slowly slows down to idle.
Any ideas of what to check first?
carb was rebuilt last year and hasnt been giving any problems , that doesnt mean thats not the problem... but..
i dont know. all vacume lines are ran/pluged properly and no vacume leaks can be found. timing was set not long ago, it has electronic ignition conversion that was regapped not long ago. and new cap/roter/button/wires/plugs.
I am a little dissapointed. the heads that the machine shop said were "good to go", obviously are not. after we got it running i started pulling plug wires off in succession and pulling the #2 wire has little/no effect. so i did a compression test. it tested at 90 psi. where 2 weeks ago with the old heads it tested at 115-120 psi.
is there any thing i can do to diagnose what is wrong with the valve train on they cylinder without taking a bunch of stuff back apart?