sadly it turns out, that the exhaust thread repair does not hold (see Post http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=364273#Post364273
It comes out of the head more and more, so that the exhaust pipe can't be fastened anymore. So I stripped down head and barrels again and noticed, that the
new JP piston had already a seizure and has to be renewed as well. The cams look good. I measured the endplay of the camshaft. It is about 0.15" (0.4mm).
Is that still in limit ?