This is a post for information only, really... I have and XJ 600, pre diversion, which for a long time ticked quite severely from one side of the head. After much searching groups and general head-scratching, I discovered that the ticking was caused by a bad seal where the exhaust downpipes join the cylinder head. Basically the problem just got worse until it was kind of obvious, from the sound of the exhaust, that gas was leaking out in a big way! I took the exhaust off, thoroughly cleaned out the recesses where the collapsable ring gaskets went, and indeed found that the pipe in question actually had the remains of an old gasket underneath the current gasket. I replaced all the old gaskets, using the copper type rings, also using a smear of exhaust repair putty, just to be sure and carefully re-fitted the exhaust. This cured the problem and seemed also to restore a little lost power, and certainly made the engine idle a lot better. It sounded a lot nicer too... One additional symptom that's worth noting was that the inside of the downpipe on the affected cylinder was light grey in colour (the others were black and a bit sooty!) seeming to indicate that the leak was causing this cylinder to run a lot leaner and hence hotter.... Oh well, not really inviting any further comment, but I hope this post saves someone a bit of time...
