what's with this piston?

[Winston-Rover]

I finally got around to stripping my '71 IIa down for rebuilding. I just pulled the head and noticed the 3rd piston looked different than the rest (note the small circle with center indent in the center of the piston). is this a piston repair or a special type of piston? IIRC this is the same cylinder that gave me low compression when I checked over a year ago (don't have my notes in front of me). I also found what looked to be bits of broken piston ring in the oil sump. Guess this means I'm in for reboring and new pistons?

How do I tell if the head has been setup for running unleaded fuel?

I've been documenting the whole teardown process and would like to start a build thread shortly. just need to find the free time.

On a side note, after I finished with the engine, I found my shop boy in the office reading the Discovery repair manual. Not bad for 2.5 year old!

[yorker]

Back in the day it wasn't uncommon to replace one piston if something had happened in that cylinder. One of my 88's had a replacement piston in a cylinder that had had a broken valve in it. If the other cylinders were still ok they wouldn't always replace them all at once- they'd do the bare minimum to get it running again and on the road.

[gudjeon]

The only way to truly tell if it has been rebuilt for unleaded is to visually check for the hardened valve seat installed on the head. With the head being off, of course. Even then, you can't tell stellite valves from original just by looking at them. A good engine machine shop should be able to tell if take yours in for rebuilding. I was lucky as my local shop has an old school guy who apprenticed in England. I got mine converted and machined before he retired. If you buy all the parts, then you truly know it has been converted.