Hi all, I have an 848 and as a winter project I decided to strip it and clean it. The belts were about due, so I did them while I was at it. I decided at this stage that I might as well have a go at checking the valve clearances. My question is; in the service manual there are two lists of clearance values. One is the ‘operation clearance’ and the other is the ‘checking clearance’. As I write it seems self explanatory but to be sure can anyone confirm which tolerance I need to be sure the clearances are within? I apologise in advance if this question/topic has already been addressed. I did a quick search of the forum but couldn’t find anything difinitive.
The 'checking' clearances is what they should be set to when adjusting them. The 'operation' clearances is the tolerance allowed before adjustment is required. So, intake openers should be adjusted to be between 0.13 to 0.18mm but they are regarded as ok if they are within the range of 0.10 to 0.25mm, although I personally wouldn't be happy if they were near to those limits.
The larger clearances are there to save the dealer money by not adjusting them until they are way out. If you're going to the trouble of doing them yourself use the tighter clearance IMO. When I do mine I make sure they are exactly as I want them, I've got the time, patience and the shims so why settle for anything less?
Thanks guys, you’ve confirmed my understanding. My horizontal left closers are both close to the operation limit. I’m going to save adjustment for the next service. Does anyone know if it is typical for the horizontal left sided closers to work towards the upper limits whilst all other measurements are nigh on nominal?
No reason that I can see why that should be so? There are those that say on the older desmoquattro where rocker failure was/is common that horizontal cylinder exhaust rockers were less prone to failure due to the pool of oil that gathers in the cover, meaning they are less likely to run dry but my experience with 916 says otherwise. Can't imagine any anomaly on 848 left side? I have no experience with newer bikes (can only speak for old-school desmoquattro and 2-valve) but as things wear the openers get tighter and the closers get looser, I wouldn't be happy to leave openers until next time if less than 0.1mm because they'll only get tighter...
Thanks. I was wondering about heat on that side of the head (less air) but then you’d expect to see similar wear on the openers. All my openers are 0.14/0.15. It’s just the two aforementioned closers that are near the operation limit.
Exhaust shims supposedly get tighter due to carbon build up, whereas intake get smaller due to wear. Therefore if you have a choice in shim sizes (not sure what increments Ducati supply them in), fit accordingly.
There's a little lost in translation. The two figures are assembly, and operational or checking tolerances. The tighter toleranced readings are for assembly if building/rebuilding and also used when reshimming once out of service tolerances have been exceeded. Closers can go wide if the half rings flatten. Always worth dropping a couple of new ones in to see if the gaps come back in spec.
I've been doing the valves on my 916 for many years and have never had a closer get tighter, and I set them nice n' tight to start with so would soon find out if they did.
I see that makes sense. Would your average ducati technician replace half rings or would they compensate with re-shimming?
The older bikes tend to widen as the valve sits in the seat deeper. The newer motors have harder seats and it does tend to be carbon build up that tightens them.. A lot comes down to set up and use as well. SBK tend to live life faster and stay cleaner.
Granted, but you do have an elephant as an avatar giving you; an air of authority, wisdom, memory and of course massive balls. In all seriousness I’ve not heard of the need to replace half rings, the manuals and forums normally refer to shim adjustment. I just wondered if you were in the know...
I've done a few over the years. Tbh, the half ring trick is an old tip I picked up many moons ago. It seems less applicable nowadays on the newer stuff, but always worth a try if you're aiming for a clearance between shim sizes, or a small adjustment, especially on the old 2V stuff. They're heavy on the rings for some reason, often breaking them. It's also much cheaper than buying new shims. If you inspect the half rings, you'll probably see the ring has a flat on it. If it has, change it. On occasion, even using the old rings and putting them in upside down to the way they were removed can change the measurement... this often leads to "the new shim is wrong". The tolerances were opened up to firstly reduce maintenance costs but also the closing springs were beefed up to help with emissions. A wide closing tolerance is less significant now due to the springs. The opener still effects running as if it's too wide you reduce valve lift. If you're within checking tolerance, or even on top value on closers, then run with it.
Good advice there Nelly. I find the same thing with half-rings but mainly it seems to affect the old 2V engines with 8mm valves stems and as you say the half-rings sometimes come out in 2 or 3 pieces. Not only that but the groove in the valve stem can develop a burr that you have to remove with emery in order to get the closer shim off. I think this is usually a result of allowing the closer clearances to get too big so that the half-rings get a beating.
I've got MBP collets in both of mine and the valves rarely need any adjustment which suggests that (at least some of) the variance was half-rings wearing. When I first got the Monster and stripped the engine there were several broken half-rings.
