Al, there's usually little or no wear on the shims. Because they are being directly acted on by the follower in a linear fashion rather than having a cam lobe rotating over them, they don't wear like a conventional valve shim or bucket.
Nelly Have you found the groove in the valve where the half rings locate can also wear causing closing float ?
A little.... Both the stem and/or shim can be affected. the stem can usually be dressed back. The shims sometimes don't fit on the dowel when measuring them or come off the stem cleanly also. I think they burr up from split or flattened half rings. Usually they can be cleaned thru with a ream to fit the dowel and valve stem again.
Thanks, I'm learning about my bike, which makes me happy. I think a diagram would help at this point though.
That's where it gets interesting AL. Neil will have more experience than me on this engine but valve train on a 2 valve seems pretty stable/wear limits acceptable and well thought out generally (re: wear) on a stock system anyway before any compromises introduced via tuning so (in my experience) first significant wear likely to come from valve seats (so closer shim clearance reduced). In the case of the 4 valve it's not as easy to call due to the rocker faces ability to wear prematurely sometimes passing this on to the cam lobes if not caught in time (so closer shim clearance increased) plus the likely hood of valve recession again although haven't done enough to come to a conclusion myself but they seem better than 2 valve here (so closer shim clearance reduced) plus the likely hood of worn/distorted collet split rings again. All in all, shimming needs to be done with plenty of care here. I'm still fascinated by the many variations that Ducati tried over the years to reduce the rocker face problem be it due to wear or chrome separation. Neil and Steve could probably write a small book on it.
I found that the closing shims were hard to remove on a 600ss engine used in DD and found the stem grove was burred very slightly. I have even seen shattered half rings on class B 600's. Brilliant thread BTW
Back when moto cinelli were trading Dad used to be able to get different thickness half rings for the bevel's.. he still has a collection of them from 1mm 1.25mm 1.50mm etc (which i use)
I think I'm mostly there with figuring out how the desmo system works...just a couple of things outstanding: -The gap between the cams and followers/rockers - presumably there's a thin film of oil which prevents the wear but still allows the cam to act on the follower? -If the valve clearances are set cold, what happens as the engine warms up?
The 600's seem to be favourites for cracking the half rings tbh. Very rarely see 4V fail. You can reduce it by filing the ends of the half rings flat. They are supplied "pointed" as if they've been simply cropped with a guilotine (probably have). This means they will butt up to each other rather than try and ride over each if/as the shim rotates. Oil is fed to all components in the Desmo to prevent wear, but yes, basically your on the right track. The clearances are in there to allow for the expansion of components due to temperature. Valve seat material, valve material and valve seat width have all been improved over the years. That's in no small part why we're seeing desmo services stretching out to 15k now and beyond for the new Hyper.
Back to Humbug's issue......... So, based on what I have read here from people that know these engines better than me; after 3800 miles, either Baines set the gaps wrong in the first place, or the valves have burned into their seats..... .....either way, I don't believe it unless Humbug has been using ethanol instead of petrol. AL
Maybe Baines checked and they were within tolerance and left alone? The clearances involved are tiny....0.05 on a closer is OK. Wouldn't take much to take that up. Valve inspection is a regular service op....doesn't mean they get adjusted every year.
ok AL - you could be totally correct, as I said, it would take a 'god' to categorically state without dismantling that any binding was solely due to incorrect shimming, as ridged valve stems/worn valve guides, worn or binding camshaft bearings etc can produce similar on other engines - there's nothing wrong with having a guess unless owner is expected to pay a bill when no damage or wear is found. ^ just what I was thinking Neil..
At first I didn't quite get it but after doing my own SS valves I know just what you are talking about. If there is a gap in the closing shim the cam will be able to rotate freely but when the gap is zero or less you can feel the cam dragging against the shim and I used this to shave 1/100's of the shim until I could feel the slightest drag and then check that I could still rotate the shim while holding the closing cam down. You know that the new half rings will settle in a bit and the gap will increase, I think there were 1-2/100 difference when changing them. I could see on my SS that the closing gaps increase while the opener gaps get smaller, I had to shave the exhaust opener shim down a bit too after changing shims and half rings. br Jim
I am convinced that the mechanic knows what he's talking about. Just picked the bike up after the valves were done, and it feels a little different to ride - the main thing is you can actually hear the tappets now! Apparently all 8 shims needed changing, as the gaps had tightened up. Still a bit of a mystery as to how this had happened in 4000 miles - but the solution may be that there are 3 or 4 missing MOT certs since when the valves were last done (2003) and now. Thing is the bike looks like it's done only 14,000 miles.. Had a nice ride home along the Thames, and just about missed another downpour this afternoon.
