Thanks for the comments chaps,
Was a bit longer than expected. It would have been back early June, but it appears "Something" had been through the engine at some point in the past. Marking the piston crowns, but not causing any damage to the bores or piston skirts..... no ideas. But the engine is 20 years old so lots could have happened in the past.
Piston skirts have the Ferrous coating later changed to plastic in later cars. Look as good as new!
Although the marking didn't affect the engine usability or performance, (Still running very well before being stripped and sent for the rebuild) I went for some new ones, choosing to use six new forged pistons from Wossner. These appear to be a good quality forged piston made from 4032 alloy and have tight piston to bore clearance of 0.05 mm.
Cost of new Porsche Mahle ones didn't stack up. I'm lead to believe that production tolerances from new are "variable".
Weight of the pistons is broadly similar I think. Wossner quotes 398 grams, but not sure if that includes gudgon pins and piston rings? The Porsche Mahle ones, together with gudgon pins and piston rings are 544 grams. I weighed one of my Mahle ones without the gudgon pin and it came in at 425 grams.
Anyway, getting hold of the new pistons caused a slight delay.
Spec is as follows:
6 x new Nikasil plated alloy cylinder liners + modify the engine casings.
6 x new forged pistons
1 x Larger sprocket and bearing on a modified IMS
Cylinderhead overhauls inc skim and cut the seats, new valve seals etc
All timing chains, rails, and tensioners changed for new,
ARP big end rod bolts
New Low temp thermostat and new oil pump spring (my request)
New bearings throughout - of course.
I broke out the "little toolkit" (Demort
) and started getting it back together this evening.....
The exhaust manifolds are being put back on with Stainless steel (304 as 316 is not as strong) studs. Marine grade washer including a spring washer locking system. Brass nuts.
Comparison with new and old manifolds. The entry hole into the manifold measure 27mm x 42mm on the stock manifold. New stainless one is 33mm x 52 mm. Both use 42mm Outside dia tube. The collector on the stock manifold is around 2 1/4 inch O/Dia. The stainless collector is more like 2 5/8 Inch O/Dia. Bends are a tighter radius on the stainless manifold though.
I'll attempt to add a bit more to this thread tomorrow...