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On the basis the original twin shock set up has 4 non-rigid links (2 top and 2 bottom of shocks), and the shocks are inherently 'flexible', are they adding any strength to the swing arm?
Or, does the swing arm rely entirely on its own integrity to resist twisting at the axle?...
Swingarm is responsible for keeping everything in align and allow free movement in only one plane, the shocks and springs only carry the live load (your bum) and in practice less then half the weight of the bike (unless you pop a big ass wheelie), top eyelets on the originals are probably even rubber so they do virtually nothing to resist lateral movement. The drive train (chain) and rear brake actually impose some of the highest stress loads that the swingarm will ever need to contend with.

Which brings up another area of concern; you can beef up your swingarm all you want but the rear hub on your bike is not particularly strong by design, you have a skinny steel axle fitted with 2 light duty roller bearings worth (about 4 bucks each) pressed into an aluminum flange that is far from optimal in its design (light duty bearings not widely spaced apart and rubber cushion drive in the hub)

lol Toni Bou would destroy that in about 10 hops, even I have completely shattered better designed hubs then that one on an MX bike.

Modern hub off a 150 pound trials bike that has about half the horses, larger bearings, fatter axle, widely spaced bearing races and superior angle on the spokes for visual comparison.
 

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Shall we move on to the swingarm bearings now?
or in the case of your CB500K1 -> bushings.
... you're beefing up the swingarm, any plan to upgrade the things that carry it?
What is the condition of your original parts?
 

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I go away for the weekend and this thread really "takes off"

ok OP I have some questions:

1) Why are you mucking about with the junk stock swingarm? With the proliferation of aluminum and even box steel arms for the last 30+ years, why wouldn't you go find an alloy arm that was actually designed to be a monoshock? The materials would be better, the machining better, the whole thing would be both stronger and lighter, and most times you can get them for around $100. Honestly I would consider shortening a GS1100 alloy arm than I would considering working with the stock cb swingarm - they weren't even good when new.

2) considering the level of modification you are looking at, why wouldn't you just remake the frame as well? There is a reason why racing never embraced the idea of a monoshock with the stock chassis - most kept the twin shocks, or remade the frame design entirely. If you have the welding skills to reinforce a swing-arm (you know they have to be jigged to prevent warping, right?) then you have the skills to build a frame, so why not?
 

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The one shown in Trial's GIF, would be relatively easy from an "attachment point of view", but that's assuming a few things. Then you would need a front end to match and you still end up with something that flexes around the swingarm pivot points, steering head and everywhere in between. From a 600RR

600RR S:arm.jpg 600RR S:Arm2.jpg
 

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The one shown in Trial's GIF, would be relatively easy from an "attachment point of view", but that's assuming a few things. Then you would need a front end to match and you still end up with something that flexes around the swingarm pivot points, steering head and everywhere in between. From a 600RR

View attachment 84833 View attachment 84841
If a smart guy was to mount an eccentric adjustment on that lower link, could make the bike ride height adjustable B)
... ya, I think our CB500K1 would whoop his CB500K1 lol and it even has a rear fender.
 

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If a smart guy was to mount an eccentric adjustment on that lower link, could make the bike ride height adjustable B)
... ya, I think our CB500K1 would whoop his CB500K1 lol and it even has a rear fender.
I would rather stab myself in the eye with a fork than have a CB500 (or any other CB for that matter) darken my doorway. Unless it's starts with CR and it's 4 stroke then I couldn't give a rats ass. I just went to undo the castle nut etc etc. on the GL500 swing arm to remove it , and I had all of the proper tools sitting in my "special tool drawer". That in itself tells me I've already wasted enough of my fucking life. Talk about a misspent youth.
 

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this mono shock fixation is a loosing game for anybody but a master frame builder with a good knowledge of suspension design
you are much better off buying some externally adjustable twin shock like what race tech fox ohlins and others offer
the twinshock geometry could be modified a bit to get the best action and a bit more wheel travel 6'' or so would give best results in my opinion ,increasing ride height at the same time an inch or so
bonus is more cornering cklearance
but you have to decide on the design ,then get the shocks properly sprung per all your data
and then build the frame and swingarm to suit because its so much better to build with the shocks in your possesion,springs removed so that you have eyeballs on what is happening
the rear frame and seat base height need to clear at full bump hence springs removed to ease observing full travel
chain slack variation can easilly be observed as well

the superbikes of the 1015cc era are good forms to follow
simply laying the top mount forward gives more travel and better geometry, into a slight rising rate
the 34 is more radical giving a higher swingarm leverage ratio than on the 140
woo (1) (1).jpg
 

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Discussion Starter #71
Swingarm is responsible for keeping everything in align and allow free movement in only one plane, the shocks and springs only carry the live load (your bum) and in practice less then half the weight of the bike (unless you pop a big ass wheelie), top eyelets on the originals are probably even rubber so they do virtually nothing to resist lateral movement. The drive train (chain) and rear brake actually impose some of the highest stress loads that the swingarm will ever need to contend with.

Which brings up another area of concern; you can beef up your swingarm all you want but the rear hub on your bike is not particularly strong by design, you have a skinny steel axle fitted with 2 light duty roller bearings worth (about 4 bucks each) pressed into an aluminum flange that is far from optimal in its design (light duty bearings not widely spaced apart and rubber cushion drive in the hub)

lol Toni Bou would destroy that in about 10 hops, even I have completely shattered better designed hubs then that one on an MX bike.

Modern hub off a 150 pound trials bike that has about half the horses, larger bearings, fatter axle, widely spaced bearing races and superior angle on the spokes for visual comparison.

Thanks for the clear explanation on the swing arm. I'd figured the vertical explanation. As you say/imply, both ends of the shocks are 'loose' (not literally but isolated to allow minor rotation). The horizontal 'twist' from the drive side hadn't got, but as it remains in line with the swing arm as spec it's all as intended.

I had a cheeky look inside the hub (photo attached) all in order but as you say nothing special.

At this stage I'm proposing to clean it up. I've built a few wheels and agree your comment on the hub width v wheel strength.

I'll post some photos of the wheels - paint flake/rust for an opinion.
 

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Discussion Starter #72
Shall we move on to the swingarm bearings now?
or in the case of your CB500K1 -> bushings.
... you're beefing up the swingarm, any plan to upgrade the things that carry it?
What is the condition of your original parts?
Best I can say at this point is all in place (including felt washers) and well greased on a bike that's done 44,000 miles.

Replacing the bushings sounds like an obvious start.
 

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Discussion Starter #73
I go away for the weekend and this thread really "takes off"

ok OP I have some questions:

1) Why are you mucking about with the junk stock swingarm? With the proliferation of aluminum and even box steel arms for the last 30+ years, why wouldn't you go find an alloy arm that was actually designed to be a monoshock? The materials would be better, the machining better, the whole thing would be both stronger and lighter, and most times you can get them for around $100. Honestly I would consider shortening a GS1100 alloy arm than I would considering working with the stock cb swingarm - they weren't even good when new.

2) considering the level of modification you are looking at, why wouldn't you just remake the frame as well? There is a reason why racing never embraced the idea of a monoshock with the stock chassis - most kept the twin shocks, or remade the frame design entirely. If you have the welding skills to reinforce a swing-arm (you know they have to be jigged to prevent warping, right?) then you have the skills to build a frame, so why not?
Trust you had a good w/e

1. Mods to the swing arm are largely to provide mounting for the mono-shock. I've seen lots of images of box swing arm conversions and researched what and how to fit. BUT, and no offence intended to any owner/builder and this is definitely a taste/style opinion, I struggle with the elegance of the tubular frame juxtaposed against the clunk of the box alloy swing arm. What chance radio silence on that one?

2. The level of modification, at this stage, is intended to be very limited - mono-shock only. Although the inputs of Trails Rider are gaining traction.
 

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a rubber cush drive of some kind is pretty much what you want on the street and those honda wheel bearings a far from light duty they will handle more load than the smaller balled units in that dirt hub

the honda hub is heavier by a lot than what it could be but plenty strong the cush drive is part of the assembly its bearings becoming a part of the assembly when axle is tightened
20mm rear axle is not like wimpy skinny its plenty big for what even a modified 500 can do
 

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... those honda wheel bearings a far from light duty they will handle more load than the smaller balled units in that dirt hub
the honda hub is heavier by a lot than what it could be but plenty strong the cush drive is part of the assembly its bearings becoming a part of the assembly when axle is tightened
20mm rear axle is not like wimpy skinny its plenty big for what even a modified 500 can do
um, that dirt hub, it has a 20mm axle and runs a pair of SKF 6004 bearings
... pretty sure his axle is 15mm although not having it in front of me that is just a quick google guess.
Register; what's the diameter of your rear axle and the dimensions of your rear wheel bearings?

oops ... Scratch that! I zoomed in on the photo and see 6304 on his bearing :| they are practically the same bearing!
 

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Trust you had a good w/e

1. Mods to the swing arm are largely to provide mounting for the mono-shock. I've seen lots of images of box swing arm conversions and researched what and how to fit. BUT, and no offence intended to any owner/builder and this is definitely a taste/style opinion, I struggle with the elegance of the tubular frame juxtaposed against the clunk of the box alloy swing arm. What chance radio silence on that one?
I mean, do I really have to point out the dangers of making engineering decisions on the basis of aesthetics? There are bikes that still use tubular steel swingarms and have monoshocks, I actually own one (Ducati Sport 1000). The tubing diameter of the swingarm is at least 5 times that of a cb550's arm and the bike is substantially lighter (368lbs vs 450lbs+ for a cb550).

Here is a pic of one for reference (it's an offset monoshock - shock only on the left side, it's also a hybrid gull arm on the right to clear the exhaust):
F61860833.jpg

If you want a tubular swingarm and monoshock, it's pretty clear the "right way" to do this is to increase the tubing size and just remake the whole arm, or in light of trying to save fabrication time, adapting an arm from something else. Working with the garbage arm of the original bike is just going to give you very pretty garbage, any improvement you think you are getting by monoshock is going to be undone by the jello like nature of the stock arm.

But don't take my word for it - put the stock swingarm in a vise, and get a piece of tubing that is the same diameter as the axle and extends past the swingarm half the height of the tire and insert it where the rear axle goes, then grab the protruding extensions and twist the swingarm by hand. What you are replicating is the twisting forces the tire exerts on the arm and is partially dampened by the twin shocks. Without the twin shocks and springs there to partially dampen those twisting forces that is what you will see on your monoshock bike and will translate into a weave during hard cornering as the arm binds and then springs back.

bikes didn't migrate to box section arms because box steel or box aluminum is cheap, they did because that design is more resistant to a twisting load than a round piece of tube. To use a piece of tube to do the same thing the size and weight would have to be considerably larger.

now, there is still a way to "do it right" and use the stock swingarm - and that is using a hoop brace top and bottom. Either way I think to be safe your upper brace (and monoshock mount) should use at least as thick diameter tube as the stock swingarm itself, the bottom can be slightly smaller but not too much (maybe 1 size down). This is not an uncommon mod (most braced arms use bottom braces rather than top), but consdering the amount of work - it might be easier to just make a new arm or use a stronger one to start with.
 

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Discussion Starter #79
The one shown in Trial's GIF, would be relatively easy from an "attachment point of view", but that's assuming a few things. Then you would need a front end to match and you still end up with something that flexes around the swingarm pivot points, steering head and everywhere in between. From a 600RR

View attachment 84833 View attachment 84841
Thanks for the thought but I'm wedded to a tubular frame solution.

Illigitemi non tatum carborundum
 

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Discussion Starter #80
because we have a $5 bet. he has to get the POS bike pictured in post #1. to run under its own power. (which included the stock swingarm). should include the stock forks too. but if he wants to change them to USD he can.(just like everybody else and just like everybody else a uncompleted project). if I lose it would be worth it just to see a completed bike.
When you lose.
 
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