Rockers, who needs 'em
An old fashioned way of opening valves (and an even more unusual way
of closing them.)? sure, but if you own a Ducati you own a whole bunch of themů.
Ducati's can suffer rocker failure; the damage usually shows itself as losing the chrome facing where the cam
It happens on racebikes but it is much more common on road bikes, ones used for lots of short trips. Much has been written on the subject; there are many different theories, and one of the main ones could easily be a bad batch of chroming, the problem seems more apparent in the higher revving 748's. I detect a large amount of frustration amongst Ducati owners as to the possible causes of the problem and the best resolution.
First we have to assume the valve clearances are within tolerance, if the valves are too tight, or very loose the
chrome is going to get a very bad time. But even if everything is set up well you can still lose chrome. We have a few ideas on this and if you can bear with us we would like to run through them with you.
Now you will have to bear with us on this 'cos first we have to tell to tell a little story.
We race(d) Supermono's, these bikes (see Supermono tech)
are one cylinder off the basic Quattro Valvole Ducati engine.
There are a few other differences, dry alternator, plain main bearings (much stronger!!), and very important for the purposes of this story, a water pump hung off the end of the exhaust cam. One major similarity is that the external oil feed is the same except the 'rear cylinder' rocker oil feed looks after the balancer mechanism instead.
The exhaust cam on a Supermono is the same grind as a Corsa or SP (916SP); but it is shortened by about 10m on the
end opposite the cam belt.
The shortened end has a slot milled in it to take the water pump impeller drive (the water pump impeller is the same basic piece as the 916 but the shaft is half the length). The slot gets badly hammered in regular use and the cam needs careful treatment, but regardless it has a limited life (when Ducati finally make the 'street' Supermono I trust they will sort this little foible out).
We had Mark Fox's Supermono in for a 102mm piston kit and a general uprate of the cylinder head; we rebuilt the
head, set it all up, and got ready to run it.
With no starter we pushed it down the road, Mono's are pigs to start when they are cold and this one was no exception, three goes and 100 yards later it ran; we turned it round and walked it back up the street to the workshop. We were blipping it to keep it running, 1500 /2000 rpm ish, the walk back took a minute, finding and fitting the stand took another 30 seconds; then the geyser of oil erupted from the side of the cylinder head.
It wrecked the belt of course, oil was everywhere.
It transpires that the other thing that is different about a Supermono exhaust cam is that it is delivered without the little blanking plug in the centre of the cam wheel end that stops the oil feed to the cams exiting straight out the other end of the cam. As far as I am aware this plug is fitted as standard in every other factory Ducati cam. The important thing is that the oil took 90 seconds, at least, to get to the valve gear! We cleaned the bike and fitted a plug in the oilway and it ran perfectly; we dump loads of oil on the cams when we build a cylinder head so there was no other problem.
Now lets think about this, a typical Japanese DOHC engine will have nice little buckets over the valves; a pool of
oil sits in a pocket above the bucket and the cam runs directly in the pool, oil is therefore present from the first second of running. With a Ducati Quattro Valvole, especially after it has sat around for a
while, oil can take up to 90 seconds to arrive. The Ducati oil delivery system has no one way valve so as the bike sits unused the oil retreats slowly to the sump. When you start the engine the oil has to come
all the way back up the long oil lines, it is not going to get there appreciably quicker if you rev it.
The cams will not notice any difference if you are sitting 'off load' or are trying to ride it; but you do have some choices that will make life easier for the valve gear.
The first choice is the number of revs the engine suffers while the rockers wait for their oil supply. The engine
can tick over at 1200 rpm and bash the rocker surface 900 times in 90 seconds while the oil comes up. Or you can run it at 4000 rpm; and the rockers will get bashed 3000 times, it doesn't take a rocket
scientist to work out that the cam follower is going to prefer the lesser of the two evils.
(as an aside when I warm up my 'street' ST4 it always seems to get to about 90 seconds before the flashing 'LO' sign on the digital display is replaced with a temperature reading, I doubt it is a coincidence).
The second choice is the oil you use. Ducati recommend Shell Advance Ultra, we recommend Rock Oil Racing
Synthesis4, others talk about Motul 2000 and there are adherents to AGIP 4t Super Racing. All of these are thickish 15/50 or 20/50 racing spec fully synthetic oils. All have very high shear strengths
(Cst's of 16 and above) and take time getting around the engine when it is first started, but they all leave a thick film of oil on everything so that weeks later when the engine is next started, there will be some
oil already there. We take apart engines that have not been run for weeks and, when they have been run on a good oil, we find a thick film of oil clinging to the rockers. It is not any where as good as a
generous fresh supply but it is a lot better than a thin film that falls away from the mating surfaces as soon as the engine is stopped. Mineral or thin 5w40 or 10w40 oils have their place, but not in a Ducati
engine. (For a little more on this see Supermono tech).
With any theory there is usually a proof, and a few exceptions. Most of the rockers we replace are on the
rear cylinder if only a few have gone, the ones next to the belt (ie. furthest away from the oil feed) are usually worst.
The front cylinder exhaust cam is usually fairly immune because a pool of oil collects in the rocker box and allows the cam some initial lubrication. As we have noted before we also have to accept that some pieces of hard chroming are better quality than others, there is always the chance of the proverbial bad batch.
You still think that the rocker should handle a few seconds of abuse every morning? Well you are forgetting why you
bought a Ducati, you bought an engine with a broad spread of power and tremendous grunt, yet still with good peak power. The key to this type of power is that Ducati Unique Selling Point; Desmodromic valve
Desmo means that more valve time area is available within a given set of cam timings, the valve is accelerated from rest to full open, and back again far quicker than with an equivalent valve spring engine. There is a correspondingly harder thwack on the rocker (and the valve collets) each time this happens.
Now let us consider in a little more detail what's actually happening, we believe that most street motor problems
are start-up related.
These problems can be addressed mostly with careful use and good oil. In extreme use, racing for instance, with regular trips over 12,000 rpm there can still be problems. We should consider more of what is actually happening here. Chrome looks flat and polished; it is electrically bonded to the surface of the rocker. The cam (on street) is covered in a black coating from the hardening it receives after machining. But it is not really this simple, the surface of both rocker and cam is in fact covered with microscopic imperfections, think of it as loads of valleys and mountain peaks.
As wear takes place peaks get knocked and shear off, unfortunately the whole side of the 'mountain' also comes away
so a new peak and deeper valley is also created; with good oil this happens slowly, in cases of very high revs, incorrect valve clearances or with no or incorrect oil this happens quickly. In very extreme
cases the chrome is shattered away from the rocker surface. Other than trying to make sure the valve gear gets correctly lubricated we modify the working surfaces by SuPerTeching them. We also do the gearbox, for exactly the same reasons, gear changing is slicker and lighter, bits last longer and power sapping friction is reduced.
SuPerTech ensures that all the surface peaks are removed, without creating new valleys; a flatter surface allows a
better and stronger oil film, the oil can do its job and it takes far more abuse to erode the surface. Used on highly stressed parts it eliminates the ability of the peaks and valleys to act as though they are two
pieces of Velcro being dragged across each other, the rate of erosion is much reduced.
We believe SuPerTech is a very valuable addition to the fight to reduce wear on highly stressed parts, the flatter
surface also allows a better quality oil film to reduce frictional power losses. We have used it for three years now and we consistently see our bikes at the top of the top speed charts. With some of our
results as a private team going against the works boys, I can only believe SuPerTech does its bit for the machines performance.
SuPerTech is at its best used on new parts, and it doesn't fix things that are already broken, but it can be used on good condition used parts.
So, to summarise, in no particular order;
1) Make sure the valve clearance are acceptable, too tight is death.
2) Give the oil time to get to the rockers every time you start the engine, call it
warming up or whatever, but keep the revs down at tickover for at least the first 90 seconds of running.
3) Use good quality, high shear strength (Cst 16+) fully synthetic oil.
4) SuPerTech all the high stress parts in your engine
Most importantly don't let all this spoil you enjoyment of one of the best makes of bike
on the planet, just cut them a little slack, if you wanted something as characterless and perfect as a fridge you would have bought a Honda!