drmini in aust wrote:
It is not a recent idea to offset bore them to 68mm, back in the 60s it was a common mod, using 68mm Hillman Imp pistons.
I built three 1220 motors back then including 2 AH Sprites. These are both still running (in Morris Minors).
IMO the biggest concern is the oilway from the pump to the relief valve, which passes very close to #4 bore. If it breaks through, you need to sleeve the oilway there with a thin steel bush and hone the #4 bore, again.
Yep, a lot of mucking around for a few more cc's and whole lot more possible unreliability, as against 80-100 thou oversize bore, standard head gasket, etc. You'll lose bugger all in hp or torque. You can get it by other means. Or just get a lazy 1275 which is more than enough.
