Originally Posted by JesseVoss
I have a 1970 MK3 with a supposed engine I am trying to restore. I ordered new pistons but the new ones are not the same size. The original pistons have a 71.6mm (2.82in) diameter, the new pistons are 70.8mm (2.79in). Which are the correct size piston for a 1275cc engine?
What brand of piston? What Markings are on the piston?
47 years ago Hepolite produced a powermax piston 20747/KR 2.78" or 70.612mm
So your new pistons are probably standard, and your original pistons were probably +0.040"
Now as you ask what is the correct size piston for a 1275 cc engine that is usually determined between you and your machinist.
Options are to go +0.060" over (or to 73 mm, or 73.5 mm) i.e. around 1380