I am probably going to have to split the cases , as the saying goes . So I used a camera probe to check out the cylinders and this is what I have in my 77 supersport . I should have a rounded dome piston , yes ? And this bad boy has 4.0MM stamped on it . Unfortunately this is the only readable piston as the others are all carboned up . There is a brand ( I think ) above above the sizing stamp , but it is almost impossible to read . I think I can see a H in it ........ but ? So does anyone recognise this type of piston and or what the size stamp means please