I agree that screw adjusters are fine for standard valve gear. However, a DESMO engine needs extreme precision in valve adjustment. You're trying to get both openers and closers where they essentially have zero clearance when the engine is fully warmed up, and a tiny error can give you a tight valve, or negative clearance. This can chew up cams pretty quickly. My experience with the screw adjusters is that they're easy to use, but it is extremely hard to get a precise clearance with them.
Jack in NY
On 12/23/2010 7:23 AM, Robert McNabb wrote:
my 74 750 GT was a springer head with screw adjusters. I think screw adjusters have proven they hold up since many engine makers have used them over the years.
BMW used them on the M20 engine and it's one of their most dependable engines ever.
Chevy small blocks had screw adjusters, probably the best engine ever built. :)
Robert McNabb
Blue Ridge Mountains, Virginia
ST4 1999 RED
--- On Wed, 12/22/10, Nick Alaniz <nicktoh@comcast.net> wrote:
From: Nick Alaniz <nicktoh@comcast.net>
Subject: Re: [DucatiST] Dr. T's Ducati Desmo sketches?
To: "st2 owners" <st2_owners@yahoogroups.com>
Date: Wednesday, December 22, 2010, 5:23 PM
Actually, The 860/900 GT's from the 1970's had conventional valve springs (coils) and opening rocker arms with screw and locknut clearance adjusters. I know, because I used to own an 860.
She was an ugly betty but had several advanced features.
In addition to the easy to adjust valves, she also had electronic ignition and a real oil filter. Prior Ducks only had the strainer in the sump, which was good for big chunks but not fine particles.
I especially liked the chain adjuster.
Chain tension was accomplished by rotating the swingarm pivot shaft via eccentric carriers.
Two carrier pinch bolts were loosened at the swingarm/frame connection, a slotted tool was fitted into the end of the shaft and rotated by socket or spanner until the chain tension was correct. Snug up the pinch bolts and done. The beauty of this system was that the rear wheel never went out of alignment, for the entire swingarm moved fore and aft at the pivot. Unsprung weight was reduced too, for the adjuster weight was at the pivot, not at the wheel axle. Brilliant.
Ciao, Nick Alaniz, 2002 Ducati ST4$, Sacramento, CaL.
----- Original Message -----
From: "Michael Heth" <mheth@motolectric.com>
To: "st2 owners" <st2_owners@yahoogroups.com>
Sent: Wednesday, December 22, 2010 1:32:06 PM
Subject: Re: [DucatiST] Dr. T's Ducati Desmo sketches? [1 Attachment]
On Dec 22, 2010, at 5:53 AM, st ryder wrote:
>
> Very cool. Screw adjustable valve clearnces? What happened to that
> idea? :-)
Shooting from the hip . . .
I don't think the screw system can hold its tolerance as well as shims.
In other words to keep the bike running right on the money you would
be doing the valves even more often than with the shims.
I think the Dr. was probably saying "could be done" but not "should be
done".
Thanks,
M./
Michael Heth
mheth@motolectric.com
(415) 992-7840
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