EM001 MAC ENGINE

Has anyone ever heard of the following two snag being encountered on a MAC (1953 alloy springer?
It only does it rarely these days but every once in a while it looses nearly all compression, almost as if someone had part pulled the valve lifter. It occurs most often just after starting, usually from cold but occasionally when hot and will even manifest itself whilst ticking over by stopping the engine. The rockers have been checked and appear to have full and free movement. The valve stems are clean and it has relatively new linered guides - which haven't helped. Followers are larger radius version (ex-Viper) heel. Valve lifter is well clear of follower when released. Plenty of oil present in rocker box and cam chest. I'm baffled and have torn it apart before now expecting to find broken rings/holed piston/headless valve etc. but no! If it stops and you persevere and kick it over, the compression re-appears with apparently no ill effects. Only very rarely can I detect a momentary loss of compression whilst riding. - Will Noble 10/4/2001

I've been trying to think of reasons why my MAC loses compression suddenly while kickstarting (but it still will start after a couple more kicks, presumably after the compression snaps back in). It has to be something binding, at a particular temperature. If it were just a speck of carbon on the valve seat it wouldn't be so consistent a problem. So either a valve is tight in its guide and/or slightly bent, or a rocker or cam follower ditto. So it should lessen with miles - and a good, lengthy thrashing should at least ease the problem - let us know if it gets better or worse, meanwhile we'll see if anyone else knows a cause. - TW