This is a 79.6mm +0.020thou (500cc) forged slipper piston to fit Norton International and Longstroke Manx 79 (and 79.6)mm x 100mm Longstroke singles. Manufactured by top performance piston manufacturer - Omega Pistons.
They are high quality forged 'slipper' type pistons, which have been made identical in all vital dimensions to the pre-war type Hepolite Ref 5288 piston form, one of these being supplied to Omega as a pattern. This piston form was the standard higher compression piston suitable for petrol (rather than a 'dope' piston), as fitted to Norton International engines. Although I cannot be precise - the last time I fitted one of these original Hepolite pistons to an International engine it gave a compression ratio of approximately 9.5:1.
This listing is for a piston to fit a Norton International engine - i.e. the piston is designed to take the International conrod which has a Little End width of 1.200" (if you are not sure - check the width of your conrod - original Racing International/Manx conrods had a slimmer Little End width of 1.000", if you require the Manx width, see the seperate Item listing for the Manx type piston). As you can see from the photos, the profile of the crown, and its position in relation to the gudgeon pin centre line is identical to the original - and as far as I am aware, this is the first time this pre-war type piston has been available for many years, so you can be confident it should be as per originally fitted. Please Note: Before ordering check compatability with your own engine - later Manx's and some late Internationals had a shallower top barrel spigot and these pistons may sit too high in the barrel for those engines without some form of spacer - email me if you require more details. This piston is to fit a bore size of 79.6mm +0.020 thou (i.e. 80.13mm). 79.6mm was the standard (STD) bore size for a SOHC Manx Norton (i.e 499cc rather than 490cc of the roadgoing International . . . the racing bikes did not want to waste available cc!). If you are fitting this piston to a Norton International : then STD +.020" Manx - (80.13mm) equates to International 79mm STD + 0.045"
Weight of piston with rings/circlips etc is @465g