Ok, I now have a pristine cylinder head ready to marry up to the block, but I'm concerned about number 4 piston.
The outer edge of the piston crown is badly pitted - see photo. All piston rings appear sound as there was good compression prior to head being removed, and oil soak test shows no oil seeping past rings.
Any forum members in a postion to comment. Is piston failure likely? I dont have the facilities to hoist the engine block out, can big end bearings be reached from below the car, and piston pushed out? Finally, how much would a replacement piston & ring set cost?

That looks like a spark plug insulator fell apart and bounced around before being ejected. Do you remember a clicking noise at any stage? Mine was just like that at last hg replacement and no problems so far.

Cheers, I hadnt considered that angle.
I reckon the damage was done long before I owned the car. My suspicion is that there has been a HG failure (It is after all a Punto). There were dark witness marks on the head before it was skimmed.This allowed coolant into the combustion chamber. During the combustion process the water is instantly turned into superhet steam. This weakens the aluminium piston head and causes pitting.

Thanks for the words of encouragement though. I'm in two minds. Obviously I should change that piston, the engine being stripped down this far. However, the car is a 'spare'. I bought it as a learner-mobile for my 18yr old twins. but neither have really engaged with the ida of driving. They seem to prefer 'Dad's Cabs'

But should either of them ever learn to drive, I want the little Punto to be reasonably reliable.

Decisions decisions.....

You can get to the big ends by droping the sump, i would leave it, iv seen alot worse.

Simples31 said:

Cheers, I hadnt considered that angle.
I reckon the damage was done long before I owned the car. My suspicion is that there has been a HG failure (It is after all a Punto). There were dark witness marks on the head before it was skimmed.This allowed coolant into the combustion chamber. During the combustion process the water is instantly turned into superhet steam. This weakens the aluminium piston head and causes pitting.

...

Click to expand...

Nope, only things to cause pitting will be detonation or ingestion... and that definately looks more like a hard foreign body has entered the cylinder.

What was the state of the combustion chamber in the head?

That's not water damage , it's hammering. If you look at the head you'll see the only place it can happen is exactly where you have the damage. Would take a lot more than that to make me go rummaging down the bottom end.
If your old head is clean i.e. free of matching marks then the piston has been like this since the last hg job.

Head is A-OK

Picture below of head prior to skimming, and pistons prior to clean - up.

Think you can safely say the piston damage predates the last hg job.

Simples31 said:

Head is A-OK

Picture below of head prior to skimming, and pistons prior to clean - up.

Click to expand...

That head looks remarkably clean for one that's just come off? Also the head thickness indicators look very thin- you didn't have much taken off did you?

Something was been Burnt badly in those cylinders!
Fu... me! - Take it was burning alot of oil?

Tbh i'd be tempted to say try the piston tbh, it shouldnt affect head so try it and see how it goes

ziggy