Bumping up this thread again.
I've been reading service bulletins (to bad I dont have them all) this weekend, and here is maybe some information your guys may like to know
266:
New crank and clutch (1/2" UNC to M10×1-V
266 SE s/n 6024957
266 SG s/n 6080640
61 s/n 6051313
HS 224 carb:
266 SE s/n 5312370
266 SG s/n 5160935
254:
New starting house and XP/XPG was introduced:
S/n 0150175
Conrod bearing went from 14mm to 15 mm:
S/n 3360001
Oil pump prepared for the new oil worm gear:
S/n 3450001
262:
Conrod bearing went from 14mm to 15 mm:
S/n 3359195
Oil pump prepared for the new oil worm gear:
S/n 3450001
42/242:
Conrod bearing went from 12mm to 13mm:
42 s/n 4110291
242 xp s/n 4130001
242 xpg s/n 4110001