Looking for advice - 2012 Monster 1100evo Recently very difficult to start. Checked compression when not starting and around 25psi !! After eventually getting started and run up for a few minutes, carried out another compression check and now around 120psi - whats going on? Thinking might be valve clearances and being "sticky" when cold??
So…..ChatGPT suggests Desmo Valve System: Unlike spring-return valves, Ducati valves are mechanically closed. If the closing shim clearance is too tight, the valve might stay slightly open especially when cold, bleeding off compression. This is more likely if you recently had a valve adjustment, or if the bike is due for a desmo service.
Could be valve clearances but, could be something more serious, especially if oil consumption is up? I had a BMW 323 (car) that suffered from the infamous Nikasil bore wear and sometimes it would just spin whilst trying to start with no sound of any obvious compression. Once running though it was fine as a bit of heat seemed to seal everything back up again. I'd be checking the valve clearances first though plus, 120 psi doesn't sound high enough to me.
almost certainly valve seat recession which is quite normal. Exhaust valve shim in particular will eventually lose any clearance with almost exactly the symptom that you describe. Mileage at which total loss of clearance occurs varies from model to model and is almost non-existent on later 4v/water cooled, but can be as low as 20k miles on 2v aircooled depending on how engine used and ambient temperature etc. Haven't done one for a while but if you have a grindstone and are at home using it, then 1 shim can be done in as little as 15 minutes. Worst bit can be sliding rocker arm across in order to remove shim when no clearance present.
there's several ways to skin a cat, I'm sure it works a treat. With the way my coordination is going, I'm not sure if I'll be able to do the same method any more, but I have a lovely shim holding tube which I bring up to the side of the Grindstone and carefully rotate using both hands, in a similar way that you sharpen a drill, inbetween periodically measuring. It's very satisfying once you get your eye in.
