--------------------------------------------------------------------------------------------------- Was seeking to clean the rings on the pistons and when I was removing them, nearly half of them broke! I think the engine (which was reported to have been running hot) was in a very unhappy place. I'm going to make it happy, I think, and make the plunge to buy new pistons and rings and just move on with the rebuild. Eventually I get back to the body, but owing to the $$ spent on motor, I'll definitely be looking for the most economical approaches to fixing the floor pan (and anything else!).
I've been looking back over your pics of your engine as you disassembled it. I always look carefully at what I find when stripping an engine and try to figure out as best as I can what may have happened in the past to leave such 'marks' or damage. I suspect that your engine was 'worked on' and then covered not too many miles before you bought the car.
You mentioned in an early post that you suspected it might have a cracked head and it wasn't running. you found the cooling system badly choked with rusty debris (so presumably no anti-freeze had been used), missing studs on exhaust manifold (iirc), an incorrect crank pulley nut had been installed, and signs of foreign debris damage to the piston crown and corresponding area or cylinder head located within the cylinder. When I looked at your pic of No. 4 piston, I initially thought you had done an excellent job of cleaning it, but then decided that it was too clean, no blow-by type of staining on the piston skirt, no wear marks on the piston skirt and the surface finish on the piston skirt is not as smooth as on original Fiat pistons, nor do I see any of the original piston crown markings found on Fiat pistons.
My conclusion is that your engine had a problem and sustained damage resulting in a quick/cheap repair. I'm wondering if piston no.4 was replaced or possibly all new pistons were fitted (it is possible to buy single pistons and indeed single piston ring sets), you haven't said if the cylinder bores are still standard (84mm?) size or have been rebored?
It's very easy to break pistons rings when trying to remove them (they're usually cast iron so quite fragile) even when using the correct piston ring pliers.
Before removing rings, it's useful to make some measurements using simple feeler gauges to check for ring side clearance (i.e. up and down) in the piston ring grooves to get an initial indication of piston/ring wear. It's important to mark the top of each ring so that it can be refitted the correct way up (there are usually marks indicating the top surface on new rings but these can be worn away in use - the sealing edge of the compression rings is very carefully designed, some have a taper of only a few degrees - so indiscernible by eye, hence the need for 'top' markings, 2nd compression rings often have a tiny undercut that acts as an additional oil scraper, again important that it's fitted the correct way up. Many people think that the 'springiness' of the ring is what does the sealing - that's only part of the equation, gas pressure also acts behind the ring pushing it against the cyl. bore.
When examining pistons with a view to possibly re-using them, one thing often overlooked is if the top and bottom of the ring grooves are still parallel -
the top surface of the ring groove wears, usually in a tapered shape, the top ring groove can be badly affected, particularly on engines that have a choke (i.e. carb models) and do a lot of short runs in cold climates. The top piston ring can wear so that it has a hollowed-out shape, normal thickness at the outside edge but hollowed out further in, inside the piston ring groove - this is bad news, the ring is no longer being correctly supported, it flops up and down in it's groove each time the piston changes direction and also flexes, altering the angle between it's sealing face and the cyl. bore - it also can result in the ring shattering into small pieces particularly on engines that are revved hard from cold - the shattered ring results in poor compression, and the bits of broken piston ring can work their way past the top ring land (the part of the piston above the top ring groove) into the combustion chamber and get caught between the piston crown and the cylinder head resulting in strange 'pock marks' - similar to your engine damage in no. 4 cylinder...
Some of the marks on your piston remind me of the damage caused by the engine ingesting a small washer, typically a 6mm Belleville type spring washer that Fiat use in some areas. Sometimes the errant washer or the bits of broken piston ring will be ejected out the exhaust port if the engine is revved-up.... How might a washer get into a cylinder? possibly dropped down the carb choke while the air filter is off - it's important to check that nothing has accidentally entered either the intake or exhaust manifolds before refitting them to an engine.
I've stripped many older Fiat engines and have often found the top piston rings shattered into pieces. Have also found the oil control rings and their oil drainage groves/holes completely blocked by sludge/gum rendering the oil control rings unable to do their work....
As regards the current state of your engine...
It's possible you don't actually need new pistons, if they were replaced in the past.
I thought you deglazed the cyl. bores using stones with too coarse a grit. When simply deglazing a bore before fitting new rings, I prefer to use a 'ball-hone' type of tool (brush-style hone), it's a lot gentler. The flat stone type of hone is fine but I wouldn't attempt to remove the wear ridge near the top of the cylinder, concentrating the tool in this region can result in a tapered cylinder. Not a great fan of 'ridge-removal'l tools either, they remove material that locates/supports the piston at tdc.- I prefer to use 'ridge-dodger' pistons rings instead. I don't like removing material unnecessarily from a cylinder, it's easy to take 1 or 2 thou. from a cylinder when honing to remove all marks/signs of wear, result is your pistons now have 2 thou more room to rattle around in (plus piston wobble when it changes direction, altering the angle between the rings and the bore).
If it was my engine, I'd carefully check over the pistons with a view to re-using them, paying particular attention to signs of damage, their fit in their cyl. bore and possible ring groove wear. And just but new rings (preferably ridge-dodger type if available).
What happened to your engine originally?
I suspect an overheating issue. I mentioned in an earlier post about some tips as regards cyl. block preparation. I'd now recommend you remove the metal plate at the rear of the cylinder block that covers the coolant jacket (iirc, it's held on by 6 x 10mm headed bolts and will likely have to be prised off, I suspect Fiat used a gasket adhesive originally. Also remove the 4 (or 5?) core (frost) plugs in the coolant jacket and use a stiff wire with a 90* bend on the end to loosen/rake out any remaining rusty debris around the cylinders - I suspect you'll find a lot of rusty debris behind the metal cover plate and the core plugs may be almost rusted through, given the state of your engine cooling system. I note you have used a pressure washer and got a lot of rusty gunk out but that space at the rear of the coolant jacket (under the cover plate) may still be clogged up and could result in a 'hot-spot' that could cause problems in future. (many people, even professional Mechanics don't bother and think it'll be ok...).
