Clearance between desmo opening rockers

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andybaggies
Mariana
Posts: 43
Joined: Thu Nov 01, 2018 12:52 pm

Clearance between desmo opening rockers

Post by andybaggies »

As per the subject title - had anyone ever shimmed the opening rockers float for central contact on their respective valve stems and found the clearance between the rockers up near the cam is mighty close or even touching?

Andy B
ducadini
860 GT / GTS
Posts: 290
Joined: Sat Jul 31, 2004 9:54 am
Location: Antwerpen

Re: Clearance between desmo opening rockers

Post by ducadini »

Fitting the cam without tightening it (just enough to compress the shims), then shim the closers, then the openers (just sideways, valveplay comes later). If needed You can always shim the camshaft a bit more out or in (and then the closers and openers).
And yes, it can be close in some heads, we think some of the rockers were a bit "off spec".

enjoy it :-D
ducadini
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andybaggies
Mariana
Posts: 43
Joined: Thu Nov 01, 2018 12:52 pm

Re: Clearance between desmo opening rockers

Post by andybaggies »

Thanks for the response Ducadini... and just to be clear I'm meaning the clearance between the two opening rockers themselves and not the clearance between the rocker and side of a cam lobe.
Fitting the cam without tightening it (just enough to compress the shims), then shim the closers, then the openers (just sideways, valveplay comes later). If needed You can always shim the camshaft a bit more out or in (and then the closers and openers).
That's pretty much what I do do but I didn't realise you could shim the cam it self :? The only shims I've done on the cam are on the outside of the bevel housing for moving the bevel gear in or out.
And yes, it can be close in some heads, we think some of the rockers were a bit "off spec".
And if they do touch is is best to grind a little off the side of rockers to keep them central on the valve (stem) rather than have them operating off centre.

Cheers,

Andy B
ducadini
860 GT / GTS
Posts: 290
Joined: Sat Jul 31, 2004 9:54 am
Location: Antwerpen

Re: Clearance between desmo opening rockers

Post by ducadini »

Yes Andy, we're only discussing the sideways play.
IIRC (familytime now so garage is off-limits) You should have about 1 mm to play with those closing rockers without interference with the valvestem.
If this isn't enough, I would grind a bit of the sideway shim-side of the rocker, NOT the part that runs on the cam. Too much can go wrong on that part.
As long as the width of the cam gets covered by the rocker, it's ok.
Sometimes shimming a cam a bit more towards (if possible) or away from the bevels can help.

Have fun
ducadini
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