cantilevered*
The only real problem that I have with that is that the backbone of the frame is the oil tank [OIF] and that pivot housing is REALLY in there. It’s siamesed into the frame a good half inch, so I’d have to open up a good 2"x1" gash into the back of the tank to get it off. I mean, with a welder and some steel anything is possible, I just wonder which method is actually less convoluted?
Ducati pivot bolt is larger than the triumph. It’s 20mm. It’s really just a shaft with circlip groove in each end. No real provision for any side preload.
Actually, yes. I had considered building my own swingarm and then I reconsidered it the other day. And that was a thought I had the other day while looking at that swingarm; “damn that fucker is WIDE up front.” I thought about how far out I’d have to have my rearsets to clear the damn thing. It’s really just too wide. You might have just convinced me.
Having said that, I’ve read that it’s typical to have the cylindrical needle bearings configured with the outer race as the dynamic race, with the inner race pivoting around a static shaft. Should I consider that approach?
I just typed a big post and lost it.
Late Harley 4 speed transmissions use torrington (needle) bearings in both configurations, dynamic and static cage.
You really want a ground surface with low RMS in order to not tear up the bearings. If the ducati swingarm bolt was originally used with this type of bearing, then no problem, otherwise, you may be screwing yourself.
Is the ID of the triumph swingarm pivot ~1.1085? (Basing that off your press fit sleeve)
Those needle bearings will take zero thrust load, so you will need some provision for that no matter what swingarm you use.
Okay, so static/dynamic cage isn’t super important. Noted. Yes, the Ducati shaft is ground/hardened to ride on Torrington bearings from the factory.
Yes, the ID of the pivot is right around ~1.108". I can’t remember exactly the ID right now, but I believe I planned on a .002" interference. Should I shrink that down a bit?
The depth of the counterbore in the cups for the Torrington bearings is .002" deeper than the length of the bearing and I’ve got roller thrust bearings with hardened race washers to go between the cups and swingarm. Should only need a few pounds of side preload to keep everything tight.
I suspect you could go to .003 or even .004 if you torch the mount before you put it in. Since you’re welding it, I don’t think it really matters, just want to maintain the alignment.
I don’t think you need the thrust roller bearings but it certainly couldn’t hurt!
Best type of bearing in my opinion would be a timken tapered roller with the outer race in the frame. No need for any separate thrust bearings or a precision shaft. Going to be a little larger diameter, but worth it for simplicity. Just shove a bolt through and go.
Cool. Right…in this case the interference isn’t for retention, but merely alignment.
I didn’t think I really needed them either, but there had to be some type of thrust-safe surface in between the frame and swingarm. It was either roller bearings or copper washers. The bearings were cheap enough.
Can’t believe I didn’t even think of using tapered rollers. You’re right. That would be easier. I could drop to a 15mm ID bearing and my OD would be 35-40mm, so it wouldn’t be drastically larger, and I wouldn’t need a precision shaft as the bearing doesn’t ride directly on it.
One last thing, if you run the timken setup you will need a spacer between them. Might have to play with spacer length just a touch to get correct preload. I guess alternatively, you could run low torque on the bolt and use a lock tab and no spacer.
…that rides on the shaft, and prevents the inner races from crushing and brinnelling the rollers and outer races and allows a set amount of static preload? I see what you’re up to. Good looks.
The “right” way to do it would be to have the spacer stepped and actually go into the ID of the race, but I don’t think that’s critical, I think you could just use one that’s the correct length, you will just have to align the spacer to the hole in the bearing when inserting the rod.
Here’s a bit of semi-relavant info:
http://www.shovel-head.de/tech/fahrwerk/starhub_conversion.pdf
That really illustrated your point. I understand completely now.
I like this idea MUCH better than my previous plan.
Thanks, newman.
Glad I can help. I still really think you should consider making your own swingarm. It could look very slick and really set the build apart. I may be limiting myself to what I take in but in general I don’t see that much custom stuff. I browse bike exif now and then and so many of the “customs” are just littered with bolt-on parts. That and pipeburn are really the only places I browse, though.
Oh, I’m going to. I was on the fence about it, and you pushed me off the other side.
Build it from stainless and pre-polish it before welding. I know a guy who thinks that looks great. 
That sounds like a gigantic pain in the dick. Hah. I mean, this bike and your 'Knuckle only share the fact that they have two wheels and a motor, but I seriously appreciate all of your engineering expertise. I’ll still fixture up and fabricate a swingarm from scratch, but then I’ll powdercoat it black; only to have absolutely fucking no one ever notice it. Ever. Except maybe you. And others that followed this thread. Maybe.
Jr would think it’s quite rad. He informs me EVERY. SINGLE. TIME. we drive past your dads garage, “There’s a motorcycle in there!!!” “Remember when we stopped there and saw the motorcycle!!!” “He has a motorcycle!!!” “He doesn’t have any kids” “Why isn’t he a daddy!!!” And on and on and on.
A “cafe” type build you may be able to appreciate.
I followed this along when it was being built and this guys at-home DIY throughout the build continued to impress.
THE LAYOUT OF THAT FORUM IS HORRENDOUS.
YES IT IS. I followed it elsewhere but couldn’t remember where. had to google and that’s the first place it came up on. My bad.
I remember stumbling upon that forum when I was looking at CB919’s, woof! Andy Zion is probably the owner.
Did take this from the following page that Nick linked though:
I do like that rear sub frame portion though.
A Virago is THE bike I picture when I think of the ugliest 80’s motorcycle in existence