Sweetening a Ducati cam!
What does that mean? Well, with the Desmo cam it means it will rotate 360 degrees in the head (once the valve clearance is set) with no resistance. This is assuming that the closer springs are disengaged from the closing rocker or the spring retainer as on the single cylinder engine. Why is this important, and why would anyone check it? Read on!
First off; this is not another article on how to adjust the Ducati Desmo valve system! That is in your shop manual, and numerous Websites have owners & mechanics interpretations of those manual instructions. If you don’t know how to adjust your valves then I don’t think you should read any further. If you regularly adjust your valves and are comfortable with it and all other aspects of cylinder head disassembly and reassembly then read on. This may be a very enlightening experience for the Desmo owner. The procedures I list here can be harmful to your engine if not done correctly and carefully, period!
If you damage your engine, I will not be responsible. You just aren’t the Mechanic you thought you were!
Now that you’ve read my Disclaimer, it’s time to learn even more about your beloved Ducati.
I recently restored/rebuilt a 1971 Ducati 450RT and after a complete disassembly of the engine for inspection and repair, as necessary, I reassembled using new gaskets by the book. When the bottom end was complete it was installed in the frame minus the piston, cylinder & head. With the head on a fixture I made I began adjusting the valve clearances, again by the shop manual instructions. Finding “0” clearance on the closer is a lengthy trial & error process but with patience, sufficient shims & a means of modifying those shims it can be accomplished. This is of course done with the cam at the TDC position. When 0” clearance is reached, the high point of the closer lobe will just be slightly felt as the cam is rotated. The opening rocker is an easier process, but the same items are needed, shims & emery paper (I used #320, #400 & #600). Once both closers are set to “0” clearance & the openers are set to .004” as the book prescribes, everything is good, right? Wrong!
With both valves clearances set to spec. and the closer springs disengaged; the cam should rotate freely for 360 degrees, with only the very slight (hardly detectable) resistance when the closer rocker comes in contact with the high point on the lobe. That’s the way it should work, if the cam was ground correctly. My cam was not ground correctly, and when I tried to rotate it I had severe resistance at the transition point of valve closing on the intake & valve opening on the exhaust. On the Desmo cam, the intake lobe is ground for a fast opening & slower closing of the valve, the exhaust lobe is the reverse of this, a slower opening & fast closing of the exhaust valve.
Not knowing what to do to correct this resistance problem, and no mention of the problem in the shop manual, I went to the Internet. I searched every website I could find, and no information could I find that even resembled what I considered a major problem. Was I the only one? I doubted that. I don’t think anyone else ever checked for it before. When everything is done by the book it should be good, right.
I think a lot of Ducati riders and especially mechanics put far too much faith in Ducati’s Design & Quality Control people. If you adjust your valves per the book, you will never know if this condition exists in your engine or not. Think about that for awhile. I don’t mean to alarm anyone, but think of what might happen if your Desmo engine is like mine!
Unable to find any good corrective action on the Net, I decided to do what I thought best. I increased the opener clearance on both valves to .007” and rechecked for resistance. Still there, but not as bad. Not wanting to go any looser on the openers, I increased the closer clearance to .006” to get to a barely acceptable amount of rotational resistance. This means that I had .009” too much metal somewhere. If I had gone a couple more thou on the closers it probably would have gotten rid of the remaining contact. I didn’t do that because if you must have the closers that loose, might as well remove them and let the springs do all the work.(even though the Desmo springs are not the same as the 450 springer engine, they are weaker, from, I think the 160 engine. They are primarily there to insure positive closing for a better idle performance) In my case the pieces & parts would probably last longer had I have done just that!
Having gotten the valves as good as I could, I installed the head & finished the bike. It started easily and ran fine, with little if any valve noise. Kinda hard to tell with an open short pipe.
A couple months went by and the valve problem kept bugging me. Why should a beautifully designed Desmo head be so poorly executed that the Desmodromic system is useless as originally designed.
One thing I should mention is, when I disassembled the head to inspect the valves and seats all parts were reinstalled in their original position. Only a light lapping of the valves & seats was necessary to bring them to perfect condition.
I finally decided that I could not leave the problem alone, it had to be fixed. I contacted one of the old (read experienced) Ducati tuners in LaSalette Ontario Canada, and told him my tale. Yes, he’d seen the problem, & yes it could be fixed. He said old time racers would stone the cam to bring it to an acceptable profile and the rockers could be shimmed properly. Never having met this guy or knowing anything about him, I decided to check his story. I then emailed another long time tuner in Australia, a Ducati Guru, and he confirmed that to get the Desmo system 100% that in fact the cam would need work and hand stoning was the way to do it. (I’m paraphrasing both Gentlemen) Not being real excited about reshaping the only Desmo cam I had, I started looking for another, a backup. I did find a 450 cam on ebay and got it for a reasonable price. Now I’m almost ready to start hand grinding my cam! Have you ever heard of anything so insane? All those years of seeing those fancy cam grinders at work, with the massive grinders following a master cam and turning out beautiful camshafts. Here I’m going to attempt something similar by hand, I must be crazy!
I actually thought about this for a couple months, questioning my mechanical ability & assessing my desire to reshape a cam by hand! After all, you screw it up; you don’t go to the local M/C shop and buy another cam for a 30 plus year old bike. I had a second one, but I also had doubts about doing this correctly. Actually it’s not that hard to do, provided you have the correct equipment, take your time & don’t expect to finish the task in a weekend. I would need a different fixture to hold the cylinder head at a comfortable working height. I didn’t want to have the head rolling around on the bench while installing shims, rockers, half rings, etc. I would also need a cam holding fixture that allowed easy stoning of the cam with a guard to protect the lobes not being worked on. I would also need an assortment of small sharpening stones, from medium grit to very fine for polishing the completed cam. A good place to find the stones you need is;
Hall’s Arkansas Oilstones,Inc (website,
http://www.hallsproedge.com/index.html)
For the head holding fixture, I used 4 lengths of threaded rod 3/8” diameter by 2 feet long. These go through the head with a nut & washer above & below the head. Four holes in a thick piece of wood with nuts and washers above & below clamped in a workmate style bench hold the head at shoulder level.
This needs to be stable and comfortable because you’ll be assembling and disassembling the head many times before you’re finished.
I also made a wooden fixture to hold the cam with slots cut to hold an aluminum guard that would hold the cam in place and protect adjacent lobes.
I received the seven different stones that were ordered, so it’s time to get started.
I removed the head from the engine after setting the engine at TDC compression stroke with cam timing marks aligned. With the head mounted on the holding fixture, I rechecked the valve clearances & found them to be as they were set months earlier. I really didn’t think it would fix itself, just thought I’d check.
I disassembled the head, inspecting each item much closer than I had when the engine was disassembled. I found some areas of wear that had gone unnoticed earlier. The closing rockers had very slight wear on the cam follower pad and the rocker pivot pins were slightly loose in the head, barely noticeable. The rocker pins were not worn so the looseness had to be in the head as a very slightly enlarged hole. The closing rocker pivot pin is shorter than opening rocker pin because it sits between the cylinder head hold-down bolts. This would give less area to support the pin and may have contributed to the looseness. The reason, I believe, for the looseness is because the valves were adjusted by the shop manual and the opening/closing rocker interference caused excessive strain on these pins (with less support) and caused these holes to elongate very slightly. The head was not unusable, but it’s not like new either. This is also something to keep in mind when setting the closer clearance even if you don’t have opener/closer interference!
With closing rockers removed & the exhaust valve spring disconnected I measured the rotational torque required to turn the cam, intake spring only, required 25” lbs. with dial indicator torque wrench. Disconnect the intake springs, connect the exhaust valve springs and 35” lbs. required. This amount of force would easily cover-up the interference force and allow it to go undetected if checked with springs in place. After this was known, I disconnected both valve springs and all future checking and setting will be done without valve springs.
I refinished the closing rocker cam follower pads with #400 then #600 wet dry paper, just enough to remove the wear marks. In theory, in my theory at least, these pads should not be worn! If the cam is ground properly and the valves adjusted properly, there should be little or no pressure exerted on the closing rocker arm unless overreving has occurred and valve float is approached. I would expect to see this wear on the openers, remember the rotational torque required to turn the cam against the valve springs? My openers were in fine shape with no detectable wear!
After refinishing the closer cam follower surface, I reinstall one rocker and adjust the clearance to where the rocker can just faintly be felt as the cam is rotated, a .001” feeler gauge cannot be inserted when on the high side of the cam. When the feeler gauge is inserted on the low side of the cam a noticeable drag is felt when the cam is rotated to the high side, perfect. Now remove that rocker, install the other and adjust the clearance just like the first. Leaving that rocker in place, turn the cam to the TDC position. On the single cylinder engine the timing dot will be at the 6:00 o clock position. Install the opening rocker for that valve and adjust the clearance by changing opener caps or honing the existing cap to get the desired clearance. The shop manual calls for .004”, I don’t think .005” or .006” is too bad if you don’t have the correct size cap. The opener clearance will tighten up as the valve and seat wear, the closer will loosen up as this wear occurs & the valve goes deeper into the head.
Now, if the cam is ground correctly, you should be able to rotate the cam 360 degrees with no resistance, zero, nada. I would be very surprised if that’s the result you get. Mine was very difficult to turn through the valve opening and closing. I felt like I was very close to breaking something the resistance was so high, remember this is metal-to-metal, no springs here. The area of the cam that had the most resistance was when the valve was completely open and going down the closing side of the lobe on the intake valve & on the opening portion of the exhaust valve lobe. To mark the exact position on the cam that needs work, remove the opening rocker, remove the cam, with Dykem, coat the opening & closing lobes of the cam for that valve. Reinstall the cam, the opening rocker, bearing support cap and drive gear.
Now, when you rotate the cam the Dykem will be rubbed off at the location of interference on both the opening and closing lobes. I also put my dial indicating torque wrench on at this point to see how much rotational torque is required to turn the cam. Mine was a scary, 17” lbs. on 1 valve and about 19” lbs. on the other! I don’t understand how it lived as long as it did. Remember that I only have one valve installed with no valve springs. This photo (above) shows the Dykemed cam in place with 1 set of rockers ready to be checked. Note the second valve and rockers are not installed at this point. This next photo shows the high point on the closing lobe, the area that needs work to eliminate the rotational resistance, the Dykem has been rubbed of at the high point.
Remove the opening rocker, and the cam, being careful not to disturb any of the remaining Dykem. Put the cam in the holder & install the guard. Now with a small medium grit, well-oiled stone carefully begin to hone away the high spot on the closer lobe. If you remove material from the opener lobe you will affect valve timing, that’s a no no. The high spot will be indicated as the area where the Dykem is missing. Maintaining squareness of the cam lobe is very important here, as is the contour of the lobe, centered finger pressure above the lobe does a good job at this. Don’t get in a hurry, this takes a long time, if you get tired, quit, come back later and you’ll get better results. When you think you’ve removed enough metal use a fine stone to put the polished surface back on the closer lobe. Clean and reapply Dykem to both lobes and reassemble in the head. Now give the cam a turn, the resistance should be less, use the torque wrench to see how much less. You’ll probably be surprised at how little the improvement is. Don’t despair, it will take many, many times of the same thing to get to a sweet turning cam. If you try to use power tools or aggressive coarse stones be prepared to find a replacement cam.
I did this on my cam probably 20 times per valve to get very close to perfect. It may not seem worth the effort if your engine runs OK, but those unknowns’ bugs the hell out of me. Now both my valves have less than .001” on the closers & about .0055” on the openers. Only the slightest hint of interference at the areas of concern when I started this project. With my Snap-On 0-300 in. lb. torque wrench, I get no reading when rotating the cam. During the process I could easily read 1 ½ to 2 “ lbs. of drag at the bad spots. Nuff said.
I am completely happy with the outcome, but it didn’t come easily, a lot of assembly/disassembly and this is something that should not have to be done. Ducati should never have let stuff like this leave the factory. This problem was on an old single cylinder engine that was otherwise in very good shape, showing very little, if any wear. I wouldn’t be surprised if the twins, both 2 valve & 4 valve models have the same problem. I also don’t know the twin shop manuals, I have read numerous books on the twin & never seen a reference to this problem, although other design problems are addressed. I have seen many articles on the net about twin cylinder Ducatis losing rocker arm hard coating. There are also many fixes for this problem, new coatings by different aftermarketeers, modifications by Ducati, and excuses by Ducati as to who and how the hard coatings were applied. I’m by no means a Ducati expert, but if the twins have a similar problem to the singles I can see why the hard coatings failed. Considering the higher revving twins I would think the hard coating could fail even though it was correct and installed correctly.
That’s my opinion, I have nothing to back me up other than, the way mine was built by Ducati it could never have worked properly and lived a long life. I think it will now outlive me.
I guess it comes down to; If you don’t check it you’ll never know!
(Update; I just checked with another Ducati “Expert”, in Florida, he said he’d never heard of the problem. There you go, if you never check it you won’t hear of it either! )
Bill Kearnes
November 2005
They have character, and are great to ride.