I remember the 250cc BSA 'Gold Star' from the late 60's having the same sort of chain adjustment - possibly the best designed bit of the entire machine! Kawasaki's in the late 80's (eg GPZ900) used a similar idea (later borrowed by Triumph), whereby the rear axle was held offset in two circular billets on each side of the swing arm, so you'd adjust the chain the chain by rotating the billets. Also had the side effect of changing the ride height.
Cheers - Nick
See the face, admire the bikes, yawn at the holiday snaps... http://www.worldwidewobble.com
On 23/12/2010 14:12, st ryder wrote:
Thanks for that bit of Ducati knowledge re screw and lock-nut Ducatis. That ecentric swing arm-chain adjustment does indeed sound brilliant. What happened to the idea? Too expensieve?
From: Nick Alaniz <nicktoh@comcast.net>
To: st2 owners <st2_owners@yahoogroups.com>
Sent: Wed, December 22, 2010 5:23:23 PM
Subject: Re: [DucatiST] Dr. T's Ducati Desmo sketches?
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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