The first step in this project was finding a donor 160 frame. I was hoping to find something that had been neglected, as in CHEAP, when I put the word out on the bevelheads list. The first reply I got was from my buddy Rich Lambrechts of Motofinesse, who had a 160 frame that fit the bill perfectly.
A couple weeks later I met up with Rich at the AMA Vintage Motorcycle Days at Mid-Ohio and picked up the remains of a Ducati 160 frame that some complete hack had sent him. The swingarm had been removed with a hacksaw, cutting into the pivot bosses in the process. The remains of the swingarm pivot was then removed from the frame with a sledge hammer. From what I can tell, the frame was laid down on the ground and beaten within an inch of it's life until the pivot was freed. And the subframe was bent. And the passenger peg mount was bent. And the serrated end of the footpeg mount was destroyed.
Could this frame have been brought back to factory appearance? I suppose. But it would have taken more work than any sane person would put in to it. Ok, maybe if it was a '52 Vincent Black Lightning it'd be worth it, or some old boardtrack racer, but we're talking a square-styled Ducati 160 Monza Jr here. Out came the hacksaw and off came about 8 pounds of bent and battered tubing.
Then I needed to figure out how to attach the hardtail section. I decided to mimic the original frame tubes on the chain stays, coming out of the existing brackets with a 90 degree bend and running the tube straight up to the new axle plate. I used the hole that the rear brake arm pivot went through as a locator for the new frame tubes. First I turned up a bushing on the lathe so the bit for the hole saw would be centered, then tried to mount everything on the drill press. The test holes went fine with a 1" hole saw but when I went to do the frame things started to go wrong. It gouged the surface a little but I caught it before it was too bad. I got the hole through but it wasn't as clean as I would like. For the right side I went with a 15/16" hole saw and then opened it up with a reamer to fit the 1" tubing. I thought about doing this to begin with but decided the test holes were good enough... turns out it's a lot easier to drill through a flat plate than it is to drill through a bracket on a frame... oh well. Live and learn. The fit isn't too bad, it's just not great. The right side is shown above with a straight tube poking through it. At least I got the holes lined up well enough for a tube to go through! (Maybe a little play in one of them isn't such a bad thing!)
For the seat stays I decided to bolt them to the frame, and then weld them too after everything was in place. That way I could get away with a smaller bolt, and not have to worry that if the weld failed the frame would fall apart. Belt and suspenders, I know, but I really don't see any downside. If I don't like how the bolt head looks, I'll grind it down to match the profile of the tube, braze over it, then smooth it all down so when it's painted no one will be able to tell it's there.
One issue I haven't figured out yet is what to do with the original swing arm pivot area. I'm thinking I'll just remove as much of the boss as possible, blank of what's left, and put a plug in there to match the oil drain plug on the engine?