After a big end collapsed, I rebuilt my Superdream engine with a secondhand crank & rods. It runs fine, but has a huge oil leak, apparently from the cylinder base. At first, I thought this was the o rings on the ends of the cylinders (they were pattern parts), especially when I came to replace them with Honda parts, which were noticeably thinner. It still leaked oil though. A more careful examination showed it was coming from just above the lowest cylinder fin, not below it. Stripping the top end (again!), I see there is a groove machined on the LH cylinder between each inner head bolt hole & the central tunnel the cam chain runs up. The 4 inner head bolts are partially exposed & have copper washers to stop oil leaks, but oil can get out through these grooves. Now maybe I've done something wrong & there's excess oil pressure, too much crankcase pressure or something, but I still can't understand what these grooves are for & why oil didn't escape there before - the engine was oil-tight before I rebuilt it. Anyone help ?
