Hi all, hoping for a little advice.
I'm rebuilding a longstroke and have a pair of barrels that were on 62mm original bore with signs of a seize. I bought a pair of +20 pistons (GPM/Gandini). However, the rebore chap says that at +20 there is a score in one bore that is still showing and really it needs to go to +40. I can't get +40 pistons anywhere - I can get +60.
The Hepolite reference for longstroke pistons is 10030/xx.
However, the chaps at Draganfly have said that +40 pistons are as Triumph 5T ref 11563/std (Triumph part 70-1563 - you can see what they did there!) i.e. 63mm which is 62mm +40 thou. The gudgeon pin is same 11/16". Draganfly would have supplied me with a set, but their stockist is out. I have sourced a pair of Harris pistons.
The compression height (pin centre to crown) is 1.7/16, which is a tad over the 1.5/16 for a longstroke 6.6:1 piston or 1.3/8 which I think is the higher compression version. I think it'll give about 7.5:1cr.
My only concern is the overall piston height, which is 69.85mm as opposed to 65mm for the cooking A7. Accounting for the 1/8" (1.5/16 to 1.7/16 = 3.2mm) additional compression height the piston is still a tad longer.
Has anyone tried this?