Right, never did get around to posting those pictures. Well, here goes the story of it anyway.
How I think this happened was a mixture of the oil cooler being a bit more plugged up than I thought, and the fact the car had mega advanced timing when I got it had probably already done some damage. And absolutely hammering it 50 miles or so each way to the 2CVGB national meeting, trying to keep up with my mates Ami 8. Not that you can really break the speed limit, even hammering it. I felt something was a bit wrong on the way home that day, and it seemed to not like warm starting very much. And quite a bit of oil had gone walkies.
Anyway, at this point I still had a troublesome oil leak I couldn't pin down as the engine was so caked in oily dirt as the leak had existed for many years, so I figured the best way to solve it would be to pull the engine and clean it up as best I could, and check everything was OK inside.
At this point, I just needed to strip the engine down, clean it, and put it back (or so I thought):
This thing was seriously gunked up:
At this point, I only had a brief look inside the cylinders and it looked like it was OK:
Unfortunately, I decided to look further the next day. Good thing I did:
Vertical marks = much bad, very score. You could feel them going round with a fingernail. It looked a lot worse with the barrel off.
The piston showed evidence of quite a bit of blowby, and seemed to have just started to melt in some places (this shot lines up with the score marks on the barrel. The other side was the same in 3 places)
Anyway, I got a shiny delivery a few days later of some new barrels and high compression pistons (9:1 as opposed to 8.5:1, as used in Dyane/Ami engines):
And given that this was my first timing having an engine apart other than taking the head off a Rover K series, you can imagine I was fairly happy when this happened:
Engine started back up on the 3rd attempt, I do have a video of it somewhere but seem to have lost the link.
Annoyingly, despite replacing seals, the oil leak turned out to be a corroded pushrod tube, and a tiny hole is letting it out, so that head needs to come off again. It does occassionally leak onto the drivers side brake disc, which can make for some interesting inadverent turning left if you aren't careful. Also rather annoyingly, the carburettor still has a mega flat spot when cold and has an uneven warm idle. I do have another carb waiting to be rebuilt to put back on however.
Once warmed up however, and ignoring the oil leak, the engine is worlds better. A lot more midrange poke, and you need less effort to keep a speed up once you get there. It's not quite as revvy but I'm putting that partly down to the feel of the engine being better midrange now, and it still being a bit tight after 300 miles or so.
In honesty, the car had been annoying me quite a lot doing things like this, and then I uncovered another couple of problems since and I was well on the way to selling it. However, I haven't even had it a year yet, so I think I'll keep it a little while longer, perhaps get the bodywork improved, and sort out the carb and oil leak issues. It also has mega chunky snow tyres on, so might have to help me out if the GT86 can't manage if we get a bad winter.
Just mentioning the GT86 as well, as a side note, the picture above with the engine running I was already extremely happy. Shortly before that, Toyota had invited me to go to the Goodwood FoS, and drive one of their modified heritage GT86s up the hill. We all know how well that ended...