Ducati engined café racer

[farmer92]

Looking good, are you planning on adding any triangulation to the SA, or just run it as is and see how it handles?

[Popeye SXM]

I love your work on the SA, did you have any trouble with distortion after welding? When I made mine I built a jig, a little like yours and when I removed the SA it had a twist. Are you going for twin shocks?. Looking forward to seeing the rest of the frame

[HansS]

Hi thanks.
Farmer92. No I haven't planed for triangulation. My thought is that the SA is from a dirt bike and the forces on the street should be considerable less than it's dimensioned for. I hope im right.😆.

Popeye SXM.
Yep. Rewelded it twice before I got it good enough. It's not twisted. It just got a bit tight between where it mounts on the the engine. But I made it so i will have spacers. So no worries.
Yep I will have twin shocks. Im going old school. RSU fork and twin shocks.👍

Something like this maybe.




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[slikwilli420]

Hi thanks.
Farmer92. No I haven't planed for triangulation. My thought is that the SA is from a dirt bike and the forces on the street should be considerable less than it's dimensioned for. I hope im right.😆.

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Odd assumption. Don't hope you're right, as that gets people killed. Dirt bikes are not made to hook up instantly like a street bike. Good sticky tires and you may put the arm above its limits. Dirt bike parts dont always translate to street for a number of reasons. Please do your homework and plan on having the arm heat treated afterwards.

[HansS]

Thanks for the input. Tumbs up for having concerns about my safety.
Yes it will be heat treated. I made some calculations but Im not finished with them. Also I discovered things when I cut the SA open that one can't see from the outside.
Casting is really odd. It's very thin just in front of where the shock original mounts.
I have a backup but it's not as pretty as the KTM Swingarm.

[irk miller]

Good sticky tires and you may put the arm above its limits. Dirt bike parts dont always translate to street for a number of reasons.

See: cush drive hub

[farmer92]

The biggest load on the SA will likely be from the chain pull, luckily that’s usually mostly a compressing force on the SA.
The vertical loading of the SA depends on where you place the shocks.

As you see here, the closer the mounts on the SA are to the frame, the more of a load is placed on the arm itself. If they are in line with the rear axle, there is virtually no load on the SA in that plane. (As long as the are parallel with the direction of travel)

The other loads to worry about are the twisting and sideways bending loads. Both of these are strongly helped by triangulation of the SA either above or below, or both.

One more thing when considering where you mount the rear shocks.


Ideally i suppose you would want to be somewhat in the progressive angles, and defined want to avoid the regressive angles.

[Popeye SXM]

Ha, It took me a 2nd run with the welder before I was happy too! I still had a little straightening to do. I want to heat treat mine when I am finished so please do keep documenting. I like farmer's post, I think with twin shocks done well and with your fab skills I am sure this will be done superbly, the KTM SA will take the torque/hp of the Duc engine. Love your image, Duc engine with traditional cafe lines 

[HansS]

Got some new parts. Rear shocks👍 So now i can continue with the swingarm. Got them from TEC bike parts. Looks OK. But it's not a Öhlins. They will work just fine for now. And at only 150$ I just couldn't resist.


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