it seems to happen more if an amateur has re assembled the top end.
that's usually the case, at least that's what i used to think, until it happened to the 400f that my professional hands assembled. it was then i realized, it can happen to the overall best in the land.
hey kingrabbit, there's so many minor detailed procedures that can later on be troublesome if they are not known about. and on this site sometimes the answers or suggestions just can't list them all. but an important part to the top end work is the disassembly/assembly at the point of head removal and cylinder removal can be i'm sure you know, stubborn or stuck well, but remember take your time and if you start loosing patience, stop and leave, but for sure don't muscle it out because you want to remove and replace those very squarely at least until your past the orifice and dowel height, and that's axial roll (forward) and side pitch, meaning if one side starts getting loose, careful not to pull too hard which will result in a disfigured hole. not that it's happened to me. those recesses for the little orifice valve are pretty delicate and important to stay the size they are. they'll egg shape easy.
