Scrambler to Silver Shotgun Or Yellow Desmo Conversion?

[TedsDucs]

I'm sure somebody here has done this. I have a line on a 67 250 Scrambler, all there, for a reasonable price. How hard is it to do a (not correct, but visually nice) conversion to a Silver Shotgun, or Yellow Desmo replica? Any insurmountable obstacles? Can I just put an aftermarket seat, tank, and rearsets and have it come out decent, or are there dimensional/frame problems?

I'm a competent mechanic, but will have to outsource stuff like welding....Not trying to make a perfect copy, just a cool conversion.

Thanks for any info,

Ted

TedsDucs

Posts: 5
Joined: Thu Apr 25, 2013 3:12 am

[Jordan]

Changes will be needed to frame (esp. rear loop), rear mudguard mounting holes, seat mounts (lugs welded).
Shorter forks or it won't look right, and shorter centre stand.
Mine has an hydraulic steering damper (alas) as I think the steering geometry might have upset the roadholding - threw me off with a tankslapper once. Alright now.

Jordan

[cooperplace]

I think the steering geometry might have upset the roadholding - threw me off with a tankslapper once. Alright now.

Jordan

wow, scary. Would you care to elaborate on what brought this on? It's something we all want to avoid. Hope you weren't hurt.

[Jordan]

OK - I was riding ahead of some friends, on a bitumen road that had some minor surface damage. Some of the topping (from a previous poor repair) had come off, and coming up I saw a patch that had a drop of about 2 cm. That didn't worry me, as I'd already encountered others without drama. But, this time I released one of the handgrips so I could look behind for my riding companions. That led to a sudden full lock as the wheel hit the patch, and I came down. I got some gravel rash, but was more annoyed by the bike's behaviour.
I think a good bike should cope with situations like that, but I brought it on myself by changing the steering geometry.
My guess as to the cause is that the steering angle and related trail is too steep/short, due to having shorter front forks but standard length rear suspension units.
With an added hydraulic damper, the steering has given no more trouble. I've been thinking of some shorter rear suspension, which if it works would provide safe steering without the extra damper.
Does anyone know if there exist dimensioned drawings of the the singles' frames?

Jordan

[Eldert]

Does anyone know if there exist dimensioned drawings of the the singles' frames?

Jordan

Hi Jordan

this is what i have found over the years :





the first picture is the 31.5 mm forks . they have tripple clamps with about 70 mm offset . this is really to much
if you could find some clamps with less offset you increase your trail and that is what you need to prevent tankslappers .

the later 35 mm Marzocchi forks had tripple clamps with 60 mm offset . this is a little better .
on my own 466 caferacer i used some Cagiva tripple clamps with 50 mm offset . made a hell of a differance in the steering .
another thing is a Ducati single is pretty light up front . when using tripple clamps with less offset the engine is closer to the frontwheel so you have more weight upfront .

the second picture is off the Scrambler chassis

Eldert

[Jordan]

Thanks Eldert,

The early forks drawing is new to me.

The last yellow Ducati singles had triple clamps with less offset (resulting in more trail), and these gave the most stable feel to the steering.
It would be an option, but the style of the clamps fitted to earlier 35mm forks suit the "authentic" cafe racer look better I think.

Jordan

PS: As an aside, I tried to track down some official dimensioned drawings for the famous Norton Featherbed frame. Not to found, surprisingly.

[Harvey]

Thanks Eldert,

The early forks drawing is new to me.

The last yellow Ducati singles had triple clamps with less offset (resulting in more trail), and these gave the most stable feel to the steering.

Not in your wildest dreams, the 74 450 front end was diabolical, compared to the 72 model. I have had both and the 74 could throw you over the front. If you got the front a bit light over bumps, and landed a bit crossed up, it would snap the bars back the opposite way. Just too much trail.
The 72 450 was the best handling bike I have even ridden.

[Jordan]

I didn't know about this bad effect of excessive trail. I thought it just made the steering less sensitive.
To be honest, I only rode the yellow bike for a few hours and didn't experience any badness. It just felt nice and stable.
Not that there's much wrong with the other forks.

Isn't it interesting that the singles are such good handling road bikes. To look at the frames, you wouldn't think so.

Jordan

[Eldert]

the disc brake yellow Desmo has a Ceriani front fork . forklegs are 195 mm ctc .tripple clamp offset is 25 mm .

Eldert

[StewartD]

Harvey,

That's an interesting point, your comparison between the 72 and 74 models. I've never ridden an earlier Desmo. I had a 74 disc brake 450 and it did tend to throw regular tank slappers on outback corrugated roads. I never had a problem on bitumen though. I had fitted an hydraulic steering damper to it, but this did not cure the problem on corrugated roads.

One thing about the 450 I loved was its balance and the rigidity of the fork/front brake setup. Even though it was a single disc, I could come up to traffic lights, and brake heavily at the last moment, and it would stop perfectly balanced. I could leave my feet on the footpegs for perhaps a second or two, before needing to put a foot down.

Cheers,

Stewart D