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Discussion Starter · #1 ·
How does one dial in the stock cams to optimize the engines potential? I have read here and there that they are a little off from the factory and they can be tweaked. How do you tweak them? Are the stock pullies adjustable? If not, who sells the adjustable ones?
Thanks!
 

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In a nutshell, the crux of the problem can be traced to manufacturing tolerances. If the distance between centerlines of the jackshaft in the cases and the camshafts in the heads is controlled precisely enough, along with the belt lengths and drive pulley diameters, there would be no need for adjustable pulleys.

Unfortunately, this level of precision may not practical in a manufacturing environment. That's the assumption we must make when we assume we need adjustable pulleys. It's an easy enough assumption to make, or rather, maybe an easy enough one to sell...

Following that line of thinking, we have an allowable tolerance in the distance between the jackshaft and the cylinder base decks in the cases alone, with the horizontal likely being different than the vertical. Then there is a tolerance for the cylinder height, again with the pair likely being slightly different. We shim the cylinders to establish deck height, but we are measuring to two different rod/piston combinations, each with their own tolerance build-ups. Then add the variation of the distance from cam bore to sealing surface on the head, and it's easy to see where the variation between that jackshaft centerline and camshaft centerline can vary a great deal. Assuming a fixed belt length (although those vary as well), a "tall" stack-up will advance the cam timing (by rotating the driven side of the cam pulley down towards the jackshaft), and a "short" stack-up will retard the cam timing (by allowing the driven side of the cam pulley to rotate up away from the jackshaft).

If this is the case, I find it surprising that Ducati took so long to provide for timing adjustment. The obvious conclusion is that they must have felt that these tolerance build-ups were insignificant enough to not warrant their attention. If they controlled these tolerances precisely enough, that would be true. Does anyone know if they did? If they did, then any sort of aftermarket adjustable pulleys are really just gilding the lilly, now aren't they? Is someone creating a need they can then fill?
 

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The ones I've had experience with have all been pretty close[+/-5 deg. or so] to the spec. so the tolerances must be held pretty well,or I've just been really lucky. In a street engine I don't think the differences would be all that obvious in the way it runs. There used to be offset keys available to adjust the pulleys but I don't know if they are still around though.
 

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Close to spec and close to optimum are often different. Look at the earlier link to bike boy.org It can also depend on what you seek/how you ride.

Personally I want torque rather than high rev power as I want to haul off the line and out of corners, rather than neck wringing high rev power.

Vee Two in Western Australia used to manufacture adjustable pulleys. I recall they were acquired by another company and believe the manufacture of many trick Duc parts ceased. I also recently heard that these Duc parts may well be being manufactured again. Hopefully someone can fill in the info gaps on this.

Here are some links I have kept for when I get around to checking valve shimming and timing.

This is a link to an older thread on the same subject.

http://www.ducati.ms/forums/77-sport-classic/57362-degreeing-cams-3.html

I suggest a look at bikeboy to see the potential, then the first link for some written how to check/calculate then the ducatitech link, then the final one as a video to show parts. Without rewatching, I recall the vid shows using a dial gauge to find TDC. I prefer the piston stop method as it will be more accurate.

Cam timing - Ducati Up North

cam degreeing and cylinder squish

Video: How to Degree Cams : European Cycle Services

Richard
 

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Wow - reviewing those websites and that video, all I can say is that the Italians sure like to do it the hard way.

As I've mentioned (probably way too many times...) in the past, my background is with air cooled 911 engines. With those, Porsche was kind enough to simply supply an opening spec for the intake valve with the piston at TDC. No degree wheels (which introduce error themselves), no calculations - just hard measurements. So, set the #1 piston at TDC for the left bank (#4 piston for right bank), rotate the affected cam to the specified lift as measured with a dial indicator mounted to the cam tower (5mm, 4mm, 4.5mm, whatever it is for the specific cam) and lock the cam down. Done.
 

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Higgy

I don't think hard is quite the way i would describe the desmo system.

Tricky, patience, attention to detail spring to mind.

The desmo system is one of the things that differentiates Ducs.

Valves are mechanically (lever in simple terms) closed.

Benefits - not spring closed, so not bounce at high rpm and mechanically closed means better engine braking. My bike has 50,000 miles on it and still the original rear brake pads.

Richard
 

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Wow - reviewing those websites and that video, all I can say is that the Italians sure like to do it the hard way.

As I've mentioned (probably way too many times...) in the past, my background is with air cooled 911 engines. With those, Porsche was kind enough to simply supply an opening spec for the intake valve with the piston at TDC. No degree wheels (which introduce error themselves), no calculations - just hard measurements. So, set the #1 piston at TDC for the left bank (#4 piston for right bank), rotate the affected cam to the specified lift as measured with a dial indicator mounted to the cam tower (5mm, 4mm, 4.5mm, whatever it is for the specific cam) and lock the cam down. Done.
Actually, the Italians are not the only group that sets cam timing this way. And it matters what your desired outcome is as to what method to use. The method you use for your 911 is nice for setting it to the value the factory specified, but...
Say you are trying to optimize your cam timing by advancing your intake cam 7 degrees from the spec on your 911. (totally hypothetical numbers) How much lift is that? And how many degrees does it change if your valve clearances are not exactly what is specified from the factory (since you were measuring cam lift on the cam itself rather than on the valve or lifter)?

Changing the cam timing from what came from the factory certainly can change the way a motor runs, and the numbers specified from the factory might not be optimal for you. I would not consider that to be "guilding the lilly"...

I modified the cam timing when I built up my 853 and it made a significant difference in how the motor runs and feels.
 

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Discussion Starter · #9 ·
Ok, lots of info there. I am still not sure exactly how I adjust the cam timing. Are the pullies adjustable? Or do I need to shim my cylinders???
 

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Ok, lots of info there. I am still not sure exactly how I adjust the cam timing. Are the pullies adjustable? Or do I need to shim my cylinders???
The info I posted should tell you how to calculate and how to adjust.

You will need to take off the belt covers and have a look at the pulleys to see if they can be adjusted. I think this was introduced in 2001. If not adjustable, there will be a single hole in the pulley for the bolts. If adjustable, then there will be curved slots in the pulleys.

The cylinders have nothing to do with cam/valve timing apart from making sure that the pistons do not hit the valves. Shimming, presuming you mean shaving metal off the head (where it meets the barrels) will only affect compression ratio, which is nothing to do with adjusting the position of the cam and hence inlet and exhaust opening/closing times with respect to top/bottom dead centre of the pistons.

If in doubt and you really feel this is something you need to do, then I am sure there will be a Duc specialist somewhere who can do it at a relatively sensible price.

My advice ( and what I do ) is if I don't know what i am doing, then read, read, read again, watch vids, check this forum and others until I know that it will not be a catastrophe. Like cutting something - measure twice and cut once.
 

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Discussion Starter · #11 ·
Ok, my bike is a 96 900SS. If my pullies are not adjustable, can I buy adjustable ones? Or is it recommended to modify the originals to make them adjustable? Is the gain really worth the effort?
 

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Ok, my bike is a 96 900SS. If my pullies are not adjustable, can I buy adjustable ones? Or is it recommended to modify the originals to make them adjustable? Is the gain really worth the effort?
Unless a previous owner has bought adjustable, then your's will not be.

You can buy adjustable pulleys. I guess it is possible to get the stock ones machined.

If there were adjustables in there, then why not chase what is there.

Is it worth it ? If you think the bike is constraining you, then maybe yes. If the bike is quicker than you, then no.
 

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Discussion Starter · #13 ·
Awesome. It is a project bike, and it has not yet made it into my shop. I will inspect the pulleys when I give it a good service. Thanks for all the info!
 

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Great discussion, guys. Your points are well taken.

Punch, I was probably unclear as to what I was refering to as far as "guilding the lilly". I didn't mean the Desmo system itself; I was refering to the method for setting cam timing. It just seems overly complicated to me, having grown up using the lift at TDC method.

Austin748, I hear where you are coming from. Fortunately, in the 911 world, the whole discussion revolves around lift at TDC. We advance and retard cam timing for different power charicteristics in that world as well, we just refer to it differently. For example, we will advance a cam .5mm or 1mm, or retard it the same amount. Same idea, just a different way to measure it. I feel it's a more accurate method than introducing a degree wheel and pointer, but maybe that's because I'm more comfortable with it.

Oh, and when setting timing, we just set the valve at zero lash. We also use a tool to fully tension the back side of the cam chain, an important step I don't remember seeing mentioned in any of the above referenced material.
 

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Hi,

The belts should be installed and tensioned correctly before attempting to dial in the cams.

The cam lobe center is found buy taking the Deg mesurement at .040" lift. No need to run zero clearance...

I don't like the TDC piston stop method and have always used the dial gauge method. Just gotta rock the piston back and forth to make sure you have TDC.

For me +-1Degree is on spec.

To answer the original poster: I would do pipes/collector mod, jet kit, and filter/open box first.

Gray
 

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Running tension vs. the tension required to accurately degree the cams are two different things. Running "tension" is anything but, with 5mm clearance between the tensioning pully and the back of the belt on the horizontal cylinder, and 6mm clearance on the vertical. Setting cam timing with the belts this loose is a very bad idea. The camshaft, even with the minimal spring pressure exerted by the desmo valvetrain, will tend to snap backwards or forwards unless the belt is fully tensioned.
 

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Without adjustable pulleys , you use offset cam pulley drive ( woodruff ?) keys . They come in 2 degree increments . Both my 750 track bike and my 944 street bike use them .

Ron
 

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Hi Higgy,

When the belt drive motor is running the belts are bouncing all over the place. I know(knew) the crew cheif fron Vance and Hines when they were running Ducatis. He told me a few things about them.

The belts strech when you tension them, hense tension... The belts are not loose and rotating the motor at all will cause the belt to move the cam. Readjusting the belt tension after you degreed your cams may put them off.

I would tension the belts correctly then time the cams. You don't have to, it is your bike do what you want.

In my 20's I worked as a race bike mechanic and timing cams was something I did almost everyday. I am just trying to help you guys out.

Gray
 

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I'm sorry Gray, I really don't want to sound argumentative, but you have a few very important things completely wrong.

No, the belts don't "bounce all over the place". This would negatively affect cam timing, making it quite erratic. I've lost track of the number and variety of motors I've built in over 30 years as a hobby and race mechanic, many of them belt drive (DOHC Alfa fours, Cosworths, and some far more pedestrian than that). Some, like the Alfas, run open belts. I've watched a lot of them run, and the belts never "jump all over the place". Running my 900 SS with the belt covers off, just out of curiosity, shows the belts running quite smoothly, just as every other motor I've ever built or worked on has.

No, these belts do not stretch. Not under the running load they see with a low drag desmo valvetrain, nor with the fairly high running loads they see with traditional (and very heavy race) valve springs. These belts have internal, longitudinal aramid and/or kevlar belts woven into them. These fibers have a higher tensile strength than equivalent steel strands. Any sort of reasonable tension, enough to take all play and backlash out of the system, will not stretch them either.

We in no way "stretch" these belts when setting the running "tension". "Tension", as a matter of fact, is quite a misnomer. We are more accurately setting cold "slack", that will be taken up as the motor heats and expands. Again, 5mm of "slack" between the idler pulley and the belt on the horizontal, and 6mm of slack on the vertical. Removing the allen wrench (or whatever is used to set this slack) leaves the belts rather, well - slack, on a cold engine. Cams simply cannot be accurately timed with this slack in the belt.
 

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Connecting up a strobe and shining it on a cam belt with the engine running should settle any disagreement. Nevr done it but next time I check the timing I will be tempted to have a look out of curiosity.
 
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