Rotating cams during desmo valve adjustment

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BultacoConvert
Cucciolo - the Lil Pup
Posts: 11
Joined: Mon Feb 17, 2014 5:50 pm

Rotating cams during desmo valve adjustment

Post by BultacoConvert » Fri Mar 09, 2018 10:54 am

Hi all,
It's time for my 2nd ever valve adjustment on my '78 900SD. It's been a great bike that hasn't given much trouble since I sorted it out. I was wondering about something that caused me some trouble the 1st time around. It was hard to remove the closing shims and wire collets from the valves because I couldn't rotate the cams to the point where the closing rocker can be pushed down out of the way. So I took out the closing rocker and spring to make room to get the wire collets and shim out. I like to leave the piston at tdc so I don't accidentally drop a valve in the cylinder. On the belt drive engines it's no problem remove the belt and spin the cam freely as needed. Is there a trick to do this on bevel drive engines? I'm not sure it's possible even if I remove the bevel gear from the end of the cam. I want to leave the heads on the engine and the engine in the frame.
Last time I learned to leave the closing rocker spring off while measuring/adjusting and then put it back when on I'm sure everything is set right. That way I only have to fiddle with it once per valve.
Thanks, Craig

ducadini
750 Sport [BEVEL]
Posts: 225
Joined: Sat Jul 31, 2004 8:54 am
Location: Antwerpen

Re: Rotating cams during desmo valve adjustment

Post by ducadini » Fri Mar 09, 2018 11:25 pm

I always took the engine out and the heads off.
No fuss.
But yes, I needed a second pair of hands to take it out and put it back in and a set of new o-rings.
Gives you the chance to clean and inspect other stuff also.
Didn't want to go the path of removing those bevels when I put so much time in getting them right.

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

1funduc
Cucciolo - the Lil Pup
Posts: 16
Joined: Mon Mar 15, 2004 6:50 am
Location: Surf City, So Cal
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Re: Rotating cams during desmo valve adjustment

Post by 1funduc » Tue Nov 27, 2018 7:53 pm

I have found that these old desmo cams are not really ground concentric. I always do my valves on the bench. When setting the closer rocker I always rotate the cam to find the tight spot and use that as the point of adjustment. It is much easier to do if you remove the helper spring before setting the valves. You can reinstall it afterwards or just run without. Without the springs the bike will get harder to start as the clearances start to open up with running time.

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