A cautionary tale about the 'genuine' Hepolite pistons being sold by Wassell for our classic British bikes.
I bought my 71 BSA Firebird from a chap who'd done a partial restoration including new pistons, fitted into newly +20 re-bored barrels. I rode the bike quite vigorously over a 4 year period whilst carrying out further restoration to other parts of the bike, including chrome, paintwork and various upgrades. I had covered around 18000 miles when I was throttling down to about 50mph and all hell let loose inside the engine. I immediately pulled the clutch and coasted to a standstill. After getting the Firebird home and lifting the head, I discovered something seriously amiss with the pistons being at different heights and one being turned though 90 deg. On removal of the barrel, one piston came with it and it's conrod was still carrying the gudgeon pin and the remains of one gudgeon pin boss.
The piston had failed in spectacular fashion with both gudgeon pin bosses being ripped out of the piston skirt. Luckily there was no damage to the conrod and only a small crack to the barrel skirt. I showed the piston to several dealers who supply 'Hepolite' pistons, to ask if they had ever seen anything like it, which they hadn't. There's no evidence of the piston seizing or of any pre-ignition. It's as though the gudgeon pin bosses in the piston just decided to let go. If you look at the 'good' piston, you can see at the intersection where the boss meets the skirt, that it's quite a sharp corner whereas a genuine genuine Hepolite or BSA piston they have a generous blend radius. I can only assume that this is a weak spot that could be prone to fatigue failure.
It would be interesting to know weather anyone else has had a similar issue with these 'Genuine' pistons.