1966 Ducati bobber

[DesmoDog]

I could have SWORN I started a thread for this here, but all I can find is a mention of it at the end of my 160 Monza Jr thread so I guess I'll start one.

The beginning of this will be old info, I started this thing about 20 years ago. I wish I were kidding... but anyway... A long time ago in a land far, far, no, wait, different story. It was a long time ago but the story begins in Ohio, which isn't really all that far from here. I got bit by the Ducati single bug and went to Ohio to look at a 250 Monza. The guy selling it also had a 160 Monza Jr for sale, but all I really wanted was the 250. I mean, I DID set my trailer up for two bikes before I left, but I really only wanted the one bike.

When I got there the 250 was pretty much as advertised, but the little 160 got under my skin too so I made the guy an offer which was all the cash I had with me. I was buying the 250 either way so what the heck. He accepted it. So right off the bat, I was ending up with more "stuff" than planned. This has been a theme with singles ever since. Like a friend once said, they're like Lay's potato chips, you can't have just one.

As I worked on those two bikes, I found myself accumulating a lot of parts. It got a little silly in fact. This was when the chopper craze was in full swing, and everyone was building over tired, over sized, over powered, underbraked, overpriced choppers. I kept joking with people that I had enough extra parts I could build my own bobber as a counter point. Something small and light and cheap, using mostly leftover parts. "All I really need is a frame" was the excuse I used to not actually do it.

I made the joke one day and a buddy said "I've got a frame that would be perfect. You want it???"

Oops. Bluff called. Now what?

Can't back down now, right? Well hell yes I want it.

And so began the Ducati bobber.

What I ended up with was a Ducati Monza Jr frame that someone had used a sledge hammer and hacksaw on to remove a pesky swingarm pivot, basically destroying the rear half of the frame in the process. Tubes were bent, footpeg serrations destroyed, swingarm pivot housing mangled. It was ugly. No one in their right mind would spend the time and money fixing a frame for a 160, so out came the hacksaw and the bent up rear section was removed.

I decided the hole location for the brake arm pivot would make a nice spot for the chain stay of a hard tail frame, so I started from there. The rear is stretched a bit from what a stock 250 would be, and the rest of it worked out to fit. I bent the tubes after hours at work, then started cutting and welding and drilling and generally making a mess.

The chainstays went through the original frame and met in the middle. I put a slotted sleeve over the top of them to hold the tubes in alignment which then got welded in place. A lot of welds will have to break before this is a failure zone for the frame.

The mounts for the front seat pivot are two tabs located on a peg that goes through the frame.

The peg is threaded so the seat stays bolt in place (there are slugs inside the frame that the bolts clamp down onto). They got welded too, the bolts helped hold it all together as I was aligning/welding it up.

The axle plates were sketched up and cut out of plate.

Then the welding started. I was into home built racing frames back then and everyone was "bronze welding" them so I bought the fancy filler rod and tried it out.

Note the fancy jig aka a long board with a centerline drawn on it. Good enough for who it's for.

 

[DesmoDog]

With the tail in place the bike was ready for mock ups, tossing parts on it to see how they worked. This project took a back seat to pretty much everything else I had going on so actual progress was REALLY slow for quite a while. As in years.

This was an early mock up, pretty basic but surprisingly close to how it's turning out

I've always liked valanced fenders and thought it'd be cool to use them, but they didn't really work. I haven't got the rear seat mounts worked out here yet either.

This was a day I just started dragging things out and trying them. These mock ups happened over a period of years by the way, it wasn't a long weekend.

I did a LOT of mock ups...

Every Monza Jr on the planet has bent foot pegs by now. This was no exception and over the years I imagined a ton of ways to fix them. Most of them very complicated. Finally one day I slid an old swingarm pivot into the frame, stuck an old fork tube on the peg mount, grabbed them both and pulled the peg back into position. I got it close, went for another tweak, and broke the peg mount off. Peg mount is the hole in the center.

You can see rust on the break, which tells me it had been cracked for years. No big loss that it broke. The end of that tube had serrations on it to lock the footpeg into position, they were trashed by the guys who "fixed" the swingarm pivot, so I would have had to cut the end off anyway. Here's the trashed serration.

And here's the start of the fix. I took some round stock, drilled out the center for the bolt to go through, then turned down the end to press into the frame. For the serrated end I put a plea out on the usual Ducati forims, but nothing turned up. Eventually I took a deep breath and cut one off my other single cylinder project. It's using rearsets so in theory they will never be needed. It still hurt to cut a decent frame though.

 

[DesmoDog]

Did I mention I did a lot of mock ups?

This doesn't show it very well, but since I stuck the frame through the old brake lever pivot location, I had to come up with a new rear brake lever/pedal. The centerstand pivot seemed like the logical solution so I turned a new pivot that would mount both. I also had to cut/weld the brake arm to move the footpad on the pedal back to the right location since the pivot had moved. Seat spring mounts are starting to materialize here too. And no, I just can't get the valanced fender idea out of my head.

 

[DesmoDog]

I bought an NOS battery years ago. It's not "correct" for a Ducati but it looks the part. I considered putting some acid in it and trying to run it, but... its got to be 50 years old. It was old when I bought it, then it sat for another 10-15 on my shelf.

I like the look though. Hmm... what if I cored it out and used it as a shell for modern crap? First I scraped the tar off the top to see what I was dealing with.

Then started taking off the plastic top. I thought it was one piece, but it was three seperate compartments.

Bash the covers off and the cells pull out in one piece. Much easier than I was imagining. It's nice it never had acid in it.

One the internals were pulled I cut slots in the partitions and broke them out with a pliers.

A chisel smoothed the walls/floor and I ended up with a bare battery case with enough room to hide a modern 6 volt battery inside.

Yeah I know you can buy fake battery boxes that serve the same puropse, but I already had this sitting around, and that was the original reason for this project.

Hmm, about that... once this started to look like a real bike I started spending money on parts especially for it. The forks were the start of it, though I came really close to having a spare set of those too. In fact I do have a spare set of forks but they're upgrades intended for my 350 that I decided not to use, so the 350 kept what would have been the front end for this.

 

[DesmoDog]

Buying parts... I mentioned that because I decided to order a set of rims for this instead of trying to match something I already had. I painted the original spokes, decided to go with the stock Ducati front hub (you Honda freaks may have noticed a CB brake/hub in a few photos. The CB brake is a not unknown mod for Ducati wheels), and built the wheels.

Obviously the rear fender still needs to be trimmed. I've changed headlight shells - it's the same size (130mm) but this one has a boss for an igniition switch, plus I have the internals for it. The sidestand will likely be removed so I can use it on another bike.

Flanged rims were not my first choice, but the non-flanged rims I found that were affordable had been out of stock for ages. So, I went with black flanged rims hoping they wouldn't look as massive as silver. The day after I got the notice that these had shipped, I got an email saying the silver non-flanged ones I wanted were back in stock. Oops.

Did I ever I mention I have done a few mock ups of this along the way? I trimmed a front fender to see what it'd look like. I was a little restricted by the damage on the donor part but overall I don't think I like the shorty fender, so back to the valanced front once again. And that means the matching "round" rear fender.

 

[DesmoDog]

One thing that's obvious in a few photos is the centerstand is too long. The rear tire sits too high. The stand is basically made of a bunch of plates welded together, but they all run at angles to each other so shortening this results in that being too wide and/or too low to fit back together again. I considered solutions that involved cutting and bending and patching and rewelding, etc. Finally I took the thing off and cut the top off. Then I put the rear wheel on a block of wood and set the centerstand in place next with the two pieces overlapped so I could mark how much to cut off. Did I mention that somewhere I have a spreadhseet with all the geometry calculated to figure that out? Yeah... whatever, nerd.

I had to cut an inch out of it to get it where I wanted.

Just as expected, nothing fit back together when I was done, but all that cutting and bending and patching and welding wasn't going to fly. Instead I bought a strip of steel, laid a few pieces of it where the gaps were, and started welding.

It's no masterpiece but if you see that view once when it's installed, something has gone horribly wrong.

After it cooled down I put it on the bike and tried it out. Oops. I was shooting for the tire to be an inch and a half off the ground. It was more like half an inch. At most. Hmmm...

No worries. I also thought it was angled too far forward so I stuck an 1/8" shim where the swingarm hits the frame when it's down. Perfect. It's more like an inch off the ground now but that looks fine to me. I cut a strip of metal and welded it in place.

Don't mind the red parts, that's the stuff I 3D printed to check the fit. They are printed with TPU (Thermoplatic Polyurethane) and the only black TPU I have is four times the cost of the red I have, so I use the red for trial parts...

 

[DesmoDog]

I'm stealing most of this content from another forum I've been posting on. I'm leaving a lot of things out because I went down a few rabbit holes, one of which was 3D printing. Holy cow I've printed a lot of, wait for it... MOCK UP parts for this. I'm skipping most of that stuff for now because in the end, I didn't use much of anything I mocked up. Anyway, if you see a comment that seems out of place, it's likely in reference to something I deleted when posting here.

I hemmed and hawed about how to mount the rear fender and finally went with one idea just to have it done. It's probably way over built but at least the fender will be solid. I added bosses to the frae to meet up with an exsisting bracket on the fender.

Check out the high tech fixturing!

Tacked in place. Seems to work.

One day I went downstairs to do some cleaning and got distracted. I didn't have a matching set of levers but had been putting off dealing with it in case I decided to order a new set (or steal them off the 350). In sticking with the "use what I have around" philosophy, I modded a lever to get a more or less matching set.

Close...

And after a little nip and tuck, close enough

They need more work but that can wait until I get into final assembly mode. There are a LOT of things on this that are waiting for final assembly mode.

 

[ridesolo]

Looking good! I used bosses like that to mount the R1 footpegs I used as rear sets on my CL360.

 

[DesmoDog]

I don't even want to say how much 3D printing I've been doing, of things that mostly end up getting tossed. The good news is I finally ran out of magenta filament so no more pink parts. SO close to finishing the final part but had to change at the end. This shows a progression of battery tray designs, I've decided to make it a bolt-on part to make it easier to connect all the crap inside the battery box. The regulator attaches to the bottom.

I've drawn up about 14 versions of the strap that runs over the battery. I've printed 4 or 5. Each time I print one I think of something I want/need to change. I've printed 4 versions of the pad the battery sits on. Some of those changes forced changes in the strap. The funny part is, I finally decided to bolt the battery case to the tray which means some of the pad changes and therefore strap changes are no longer needed... I'm keeping details in the pad I don't need anymore just to use the current strap! It's like they say, at some point you need to shoot the engineer and start building the damn thing.

Here's the general idea. I'll add a fender mount also.

I still need to add the mount to the other side.

 

[DesmoDog]

I bought a tail light for this ages ago. The problem is, it's made for a larger fender. I spent a ton of time modeling and printing an adapter, then had to accept that it just didn't fit so I took the lens and trim ring off it and started working on a 3D printed version. I decided to go with an LED light vs incandescent, which aside from less heat allows a shorter/smaller body. Like everything else, it was a process. I printed quite a few of them.

The family tree. Not everything printed is pictured. The white is basically the same as the silver but has a few errors corrected and details added. Of course as soon as it was printing I thought of other changes I'd like to make.

I was printing other stuff too, including a fake oil tank that might hide a breather valve/filter. Printing's easy once the model is done, I just click the buttons and let it go while I do other things. Someone on another forum asked about videos(?) so I flipped on the timelapse option.

Yeah... 3D printing is actually kind of boring. Sometimes you have to find things to entertain yourself.

 

[DesmoDog]

I printed a chain guard too. I never really intended to use it as the finished part, it was more to get an idea of what I wanted to build, or use for a fiberglass form.

I decided on using metal though. I bought some rectangular channel and cut it up more or less like the plastic part. Cut and paste, just like kindergarten. At some point I gave up on bronze welding and bought a MIG welder. Should have done that years earlier but anyway...

A lot of ideas for an air filter too. The stock bike has a tool box side panel thingie with a filter in it. That wouldn't work here. I eventually said screw it and hit the easy button.

Before people start tossing out ads for K&N filters and other stuff, I'd like to point out this is already a huge step above my last project.

The screen on the new one will make all the difference. It'll be fine.

 

[DesmoDog]

After doing that stuff, I got tied up with other projects for a bit over a year. During that time I started using ASA filament in some of my prints. One cool thing about ASA is it can be smoothed with acetone. So I played with that.

Back to tail lights. I spent a bunch of time with LED bulbs and figuring out lights. I'll save the headlight until it's actually done, but my LED bulb festival led to a slight redesign of the tail light. After printing a couple demos of another new design I messed around with smoothing them with acetone to remove the layer lines.

Bulb and socket installed

I seem to have misplaced the trim ring but with a lens it'll look something like this.

I'm sure I'll end up painting it but I'm pretty happy with how smooth the acetone gets the surface. With this newfound trick I printed up a knob to use on a fake steering damper.

This is mid-print after a nylock has been embedded in it to hold the rod

Knob printed and smoothed, nut and spring to hold it on the ste nut and set some tension so the knob doesn't just rattle around and spin. I did the same thing on my 160 years ago and it worked pretty well.

In position on top of the steering stem nut. It could be polished but a lot of parts on this are going to look used (because they are) so there's no need to make the knob look pristine.

I also did some work on the exhaust, adding an extension with a slight bend in it to position the muffler better. Yes this is a new aftermarket muffler, the old originals I had were just too beat up to use.

 

[DesmoDog]

With this post I'm up to things I did a couple weeks ago. I've covered about 20 years of work now...

Time to work on the muffler. It's an aftermarket part - I probably should have ponied up and bought the correct style muffler for it but that ship has sailed, I'll run what I have for it. This is supposed to be a bike that's built mostly out of stuff I have sitting around after all. THAT ship sailed a while back too but still, I've got it, I should use it.

It's a simple megaphone shape but not an open mega. Those are hella loud and I hate that. Nope, this one has internals. I don't think I've shown them though? I don't know who designed it so I have no idea what their thoughts were when they came up with it, but as someone who spent a lot of his career designing mufflers, I can say that after pulling it apart I still have no idea what this person was thinking.

Shell is on the top. Perf tube and baffle in the middle, end cap on the bottom. Note the amount of fiberglass packing including. Why did they bother? Seriously, there's not enough there to be worth the cost. Whatever. That's an easy fix. Just wrap the tube in a wedge shaped mess of packing and stuff it in there.

But wait... what's this? A ring welded in there that prevents stuffing a wrapped core? WHY???? It serves zero useful purpose fro what I can tell, why waste the money doing it???

I guess that's why Gertrude Dremel invented her nifty little rotary tool we all know and love.

Much more better. Unfortunately, I'm still not to the point I can just wrap the core and stuff it all back together. The designer saw fit to stuff a perfed baffle into the tube and the hole pattern is such that there is less than half the open area in the baffle as there is in the tube.

This baffle creates backpressure. I've said a bunch of times that backpressure isn't as evil as some will have you believe, but that's regarding engine performance. The issue here is, if there's a baffle in the pipe creating a restriction, it could/will force flow through the perfs in the tube, through the packing, and back through the other perfs on the downstream side of the baffle. This would probably not be an issue on this bike, but... it's the principle of it. That's just bad design which could break down/blow out the packing faster.

I'll admit I considered grinding out the spot welds and removing the baffle, but there were 5 welds, and I'm lazy, so instead I drilled a 3/4" hole in it and then shoved a 25mm doming punch through the hole. Good enough. We're not building a space shuttle here.

 

[DesmoDog]

Here's the material I'll be using. The packing included with the muffler is unwrapped and displayed in all it's finery in the foreground. Pretty much worthless on it's own but might come in handy for wrapping the end of the tube that goes into the smaller diameter end of the cone.

I wrapped the core in more or less the shape of the shell. I could have added more but when slipping it into the shell it compresses what's there so it's close enough. And much better than the as delivered set up. I used a packing that's supposed to expand a little in use, mainly because the shape/size lent itself well to wrapping a cone shape.

This was supposed to show the packing up against the perfs but it doesn't. It shows other stuff though.

The muffler has been in pieces for years and not surprisingly I lost the screws that held the end cap on. They were trashy little self tapping things anyway so no big loss. As luck would have it, the holes were just the right size for a 4mm tap. Add a few stainless button head fasteners that were bought for some other forgotten reason, ream out the holes in the shell a touch, and it's good to go.

I'm wondering if the outlet isn't a little too large, but if it's too loud adding something to the outlet will be relatively easy later on.

 

[DesmoDog]

A big step today - I found a HUGE Ducati 750cc single engine and fit that up for size!

Ok, fine, I didn't. But what I DID do is finally put together something so I could mount a narrowcase engine on an engine stand. I've been building this in my head for 20 years and finally actually did it. Took a week, which is twice as long as I expected, but I got distracted along the way so there was that.

It's pretty simple really, just a 3' section of 1 3/4" Angle iron cut into smaller sections, then welded and drilled.

For how simple it is, I have to say I'm pretty excited about having it done.

In other news, obviously the bike is coming apart now. Time to finish up the frame so it can be painted and this thing can start going back together for real. There are a lot of little details to attend to - finish welding, add some holes, figure out the centerstand spring, etc.

And with this post, the thread is at current state of the project, From here on out everything will be real time as it were.

 

[Luugo86]

Cool project. Did you oxyfuel-acetylene torch and brazing rod those frame connections? Brazing is very strong but intended more non-structural applications when it was used a lot more back in the day. It has greatly reduced breaking tolerances than a normal weld. I know they used it back in the day a lot. I like the frame geometry a lot, did you use another frame design as a loose template?

 

[DesmoDog]

I did start out with oxy acetylene using the same rod a lot of other people were using for frames back then (and probably are still now). It's not just some random brazing rod but I can't recall what exactly it is. It's used for "brass welding" vs "brazing" but I'm not about to start arguing the difference between those. in any case, it's been used successfully for ages. Most of the joints also have a mechanical backup so if a weld were to crack the frame wouldn't catastrophically fail.

The frame geometry is basically the same as a 250 Monza with the wheelbase extended something like 2", though with the hardtail it's a little lower than a stock Monza would be when just sitting there.

 

[Hurco550]

Just got caught up on this thing. I love it. While i know next to nothing about the Ducati bevel drive cam singles, other than that they are Ducati bevel drive singles, I have always though that they were one of the prettiest motors that were surrounded buy a less than great looking "everything else". Not that I can't appreciate an old stock Ducati single, I still have always thought that the motor deserves a cool bobber looking frame. I really dig that this project is happening.

The only thing that I wish you were a little bit more clear on though.... Did you happen to do any mockups? I just couldn't tell if you had done any mockups

I am looking forward to watching this build, and it makes me really want to find a single cyl Duc lump for my next hardtail build.

 

[Luugo86]

I did start out with oxy acetylene using the same rod a lot of other people were using for frames back then (and probably are still now). It's not just some random brazing rod but I can't recall what exactly it is. It's used for "brass welding" vs "brazing" but I'm not about to start arguing the difference between those. in any case, it's been used successfully for ages. Most of the joints also have a mechanical backup so if a weld were to crack the frame wouldn't catastrophically fail.

The frame geometry is basically the same as a 250 Monza with the wheelbase extended something like 2", though with the hardtail it's a little lower than a stock Monza would be when just sitting there.

Very cool man, I didn't know there was a different brass rod that was designed for welding applications vs Brazing, ty for the new info.

 

[DesmoDog]

After years of thinking I knew how I was going to hold the rear of the gas tank down, I started working on making that happen and changed my mind. As per usual, break out the 3D printer! No, it's not vintage looking but I have other ideas and this will work until I go with a more era correct idea. Yeah, it sounds like one of those permanent temporary fixes to me too but I'm going with it. I have to keep doing things instead of spending more time thinking about how I'm going to do things when I get around to actually doing things.

That also shows the fix for the front seat mount. I screwed up originally and the pivot thingie wasn't level. So I drilled out one side in a larger diameter and had a bushing to hold the original bushing to make it all work. It wasn't pretty. It took a while but I finally realized if I put the bushings in from the back side I could use the flange thickness to replace the spacers I had planned to use. I'm changing the lathe tooling I use and couldn't remember what I had and what I still needed, so one afternoon I went down to see if I had everything to make a couple new bushings. Before I knew it I had made two new bushings so I guess I had everything. I still ordered more that night, but that's a different thread...

With that it was time to strip it down to a bare frame so I can do the final welding and clean up in prep for paint. Once that's done... it starts going back together for real.

Spot the differences! No? Ok... the bolts that were at the top of the seat stays have been welded over and smoothed. I ditched the idea of bolting the battery tray on, it's now welded. A tab was added on the frame to hold the main wiring, and a couple other tweaks I've forgotten about.

The last thing I did was try to come up with solution for a part that I lost a long time ago. One side of one end of one of the frame tubes still needs to be closed off with half a dome thingie. I bought a bunch of them when this all started and put all but this section in place. Maybe I screwed it up way back when and had nothing to replace it with? We'll never know. In any case I have a set of doming dies that have been int eh box for ages. I tried to make a dome once and it didn't work so I kinda forgot about them. The other day as I sat there thinking abtou solution (including leaving the tube open, you can't really see it very well anyway) I decided to try th edies once again. It's not a structural part so I grabbed a scrap of some rusty, thinner metal, the dies, and a sledge hammer.

Ta dah! I've got my new dome to cut up! And it only took 15 years to figure that one out.