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 Post subject: 900ss cam in Alazzurra head
PostPosted: Thu Oct 19, 2017 11:18 am 
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Posts: 172
Hello...
I just installed a 900ss OHT cam into a stock Alazzurra head. With both rockers shimmed to zero, the valve clearance measured at over .080". Plenty of room I would think. The next concern would be if the pistons are going to come up and "crash the party". I'm assuming that each cam is shimmed to fit its respective head. So changing a cam may require adjusting the shim stacks to suit? Can anyone post what the acceptable side to side tolerance is for a properly shimmed cam?
Regards...
Flattop


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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Thu Oct 19, 2017 9:43 pm 
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Joined: Thu Oct 14, 2010 7:30 am
Posts: 139
When the pulleys are done up tight the cams have no side play. The cam butts up against the bearing that butts to the spacer that butts to the outer bearing and is all pinched together when the pulley is tightened. You might have to shim it to center the the lobes on the rockers as best as you can, but that isn't a super critical measurement. more critical is getting the rockers centered on the valve to reduce side loading and guide wear. Piston to valve clearance needs to be measured carefully using clay or solder after setting your squish clearance.


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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Fri Oct 20, 2017 11:41 am 
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Joined: Thu Oct 14, 2010 11:23 am
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There is an assortment of shims for the cam cap end. But measuring is not easy. I simply shim till I can feel that the cap will not easily tighten down, and then back off (thinner, or less) on the last shim, or see if adding the gasket relaxes it. Finally just try the hand spin test.

I also try to center the rocker over the valve ends — not rattling loose, but with no binding at all. Have seen them set so tight they will wear grooves into the head. Again, a wide assortment of shims are used there, many aren't even the same diameter, and final installation is always “entertaining”.

MikeV


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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Fri Oct 20, 2017 11:56 pm 
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I suspect the shim between the cam and the end cap is more for locating the bearing in the cap to keep it from moving back and forth and loosening the fit in the cap. All depending on the fit in the head of the other two bearings on the belt side of the head. If they are loose the cam and bearings could move in the head, ultimately being located by the belt and pulleys depending on tension.


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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Sat Oct 21, 2017 4:12 am 
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i wonder if the shim on the lh end of the cam is to keep the bearing in the cap when it all gets hot? no other reason for it to be there.


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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Mon Oct 23, 2017 9:51 am 
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Good Morning....
When ever I see precision washers being used I always think there is a measurable tolerance in play. A lot of emphasis is put on making sure a crank or gear box is shimmed properly, I thought the cam would require the same consideration. I mentioned shimming the rockers to zero clearance. With the OHT cam this required over .040" in shim stock. When I put an O3 cam into the same head it didn't need any shimming as it was practically at zero clearance???? Do the shim caps come in that wide of range or would longer valves be needed for the HT cam? As it was mentioned, the intake rocker was way off the mark for being centered on the valve. Even by removing all the shims from one side it didn't look like it would be enough to move the rocker on center. Are the rockers machined more on one side than the other in respect to whether they are for intake or exhaust? Outwardly they look like the same part.
Thank you so much for your responses gentlemen.
Best Regards....
Flattop


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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Mon Oct 23, 2017 9:44 pm 
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Joined: Thu Oct 14, 2010 11:23 am
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Try this site. https://emsduc.com/

I have been buying from this seller for about 10 years. He has 8mm valve shims kits in both small and large dimensions, openers and closers. In addition, you can get individual ones in a very wide range. No need for longer valves.

The early pantah used thinner shims, and just before the small case went to the 7mm stems (696, 800, etc.) they grew larger/thicker. That is where the larger set is helpful.

I have also found that the when installing the 900SS cams in early heads that thicker shims are needed, especially for the closers. Some are very close to 8mm on the last set I did! I try for about .002" clearance. I also use the simple, can-I-spin-the-shim-with-my fingers method; should be tough, but not impossible. Finally, when checking closers, if there is ANY binding when spinning the cam then you must increase the clearance on the closers and accept a "too big" measurement.

This is one area where I think that art meets science. Remember, once we start messing with them, they are not stock. And then there are no perfect measurements to provide. The Ducati engine is, still, just and engine.

MikeV
https://emsduc.com/


Last edited by 618F1 on Mon Oct 23, 2017 9:55 pm, edited 1 time in total.

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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Mon Oct 23, 2017 9:50 pm 
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I forget about the centering. I see no difference between I and E rockers. I have not checked, but will bet that the part number is the same. I suspect that in spite of my perfect memory, and supreme organizational skills, that I have mixed them up, and survived it. Maybe it is just a matter of mass production parts. Just do the best you can. MikeV


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 Post subject: Re: 900ss cam in Alazzurra head
PostPosted: Tue Oct 24, 2017 4:25 am 
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I fitted the closing rockers first (no difference between I or E) , made sure they are centered on the valvestem.
Then shim the cam to make sure the closing rockers are centered on the lobes.
Then the opening rockers, centering on lobes and valve.
Of course this means a lot of fussing about, and it wasn't Always correct from the start, but nearly Always 99% correct afterwards.
As MikeV stated : be sure to fit everything (included the opening rockers) and then check for binding.
Then dismantle and assemble with springs.

We had a batch closing rockers regrinded and rechromed and they had a very small difference on the lobe-diameter.
This means that the point of contact on the lobe is different and the moment of contact isn't the same anymore.
What meant that the openingrocker began to push, but the closingrocker didn't give way (yet).
Being unaware of a problem, the mecanic didn't check for binding.
Fitting them and running the engine went fine, but after a few hundred miles we could throw away rockers,cams and clean the engine for debris :cry:
We suspected there is a small difference between the lobe-circle of the Pantah and the Bevels, and as we regularly let them do a batch, the rocker-man somehow messed up (or we didn't give him the correct info)

ciao
ducadini

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