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.
I’d be questioning either the accuracy of the compression gauge or the method used to check it. There’s no way an engine with just 25psi would ever start. The stated compression on that engine is 11.3:1 so you should be seeing something north of 150psi, preferably 166psi. Did you check both cylinders? Did you have the throttle held wide open whilst cranking? Dud you crank for long enough for the gauge to rise until it stops rising, each compression stroke will push it further and further until the compression in the gauge tubing and gauge is equal to that in the cylinder on a compression stroke.
Woooaa. I’m so sorry. My fat fingers 1st am have caught the wrong emblem. I meant it to be a thumbs up, for more sound advice from Paul. Could a mod please correct this for me as soon as possible? Many thanks nigel.
You have it totally wrong to say that a 2 cylinder Ducati engine won't run with cylinders* showing low compression - yes, even as low as 25 psi. Have been forced to run on one cylinder many times plus can tell you first hand that car engines can start with as low as 50 psi showing on several cylinders. Whilst it's still likely that the cold, dry, figure obtained from a compression test is higher than you think, the main thing to concentrate on this thread is surely what is causing such a disparity between initial figure obtained compared to later figure obtained after engine has run. *EDIT
Sorry, I’ve spent an age looking but can’t see how to edit the comment, it’s an age thing I guess. Could you point me in the right direction please!
To expand on that, the layout of my screen veiw is not the same as the one you posted for me. I think the computer people may call it a glitch??
On West Cork Paul's post...it appears you haven't added an icon...so you cannot undo it. Try adding a thumbs up to his post, and then you will see it.
Ahh, thank you for that, I’m not sure what’s going on, it’s like smoke and mirrors to me! I’ve taken your advice and all good again. I’m going out to my old non teccy motorbike to have a good tinker with the carburettors? Thanks for sorting me once again.
I don’t disagree Chris, I interpreted it as 25psi on both cylinders when cold but 120 after it had started and warmed up. Perhaps @evomonster could clarify?
Never, ever had a shim reduction on both cylinders resulting in identical figures that low and yet to see it happen to anyone else.
Thanks. Checked the clearances and the opening rocker has closed to zero (exhaust valve being held slightly open and causing te loss in compression) while the gap on the closing rocker has opened up and above spec. Had thought is was down to the valve stem stretching (being the "hot" exhaust valve) but valve seat recession would also make sense. Will order up replacement shims as the closing shim needs to be thicker.
Hi - yes to clarify both cylinders were around 25psi cold and both around 120psi when warm. As per other reply, valve clearances have drifted off - opening zero and closing 0.15mm or therabouts on both cylinders. I was putting this down to the valve stem stretching but could well be valve seat recession as also suggested. Inlet valve clearances still in spec.
