I did it on my Imola recently exactly as Chris describes above -- One side went in ok but the other was right b'stard. It kept pinging out as it was just on the verge of going in and every time I tried again it was scratching the piston surface. I'm hoping the scratches are inconsequential but I gave them a little rub over to ensure there were no high points.
Looking at it again, there is a small notch out in the pin bore, I think if I used a small scredriver in there to lever down one side of the circlip then it might of been easier. But I agree it's a pig of a job.
completely round piston circlip extraction/fitting
the gap in the clip should be just either side of the cut out .. there really are no bother
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