swingarm pivot

fredintoon

Fred Hill, S'toon.
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Seems to me the XS650 swingarm pivot could be improved.
Some XS650s I've worked on have had the pivot tube turning with the swingarm because there's very little stopping it moving, only the frame squeezing on it's ends and only that if it's been assembled correctly.
This leaves the de-facto swingarm "bearing" to be the tube's bore turning on the throughbolt's outside diameter.
That's steel on steel and was never designed to be a bearing fit anyway.
How about replacing the pivot tube and throughbolt with a big fat throughbolt with a hardened and ground outer diameter that fits the swingarm bushings.
Bore the frame to suit with a locking block on the bolt's head and a Nylok nut on the tail to control the end float?
Comments?
 
Snug that down and it just clamps the swingarm, it can't swing. Gotta have an inner spacing sleeve to carry the clamping force, leaving the swingarm free to move. When clamped, that inner sleeve now becomes part of the frame structure, stiffening the frame. Imagine installing one of your wheels without the inner bearing spacers.

Here's some swingarm setup info:

http://www.xs650.com/forum/showthread.php?t=1496
http://www.xs650.com/forum/showthread.php?t=1677
http://www.xs650.com/forum/showthread.php?t=25126
http://www.xs650.com/forum/showthread.php?t=25966
http://www.xs650.com/forum/showthread.php?t=28637
http://www.xs650.com/forum/showthread.php?t=29270
http://www.xs650.com/forum/showthread.php?t=30469
 
Snug that down and it just clamps the swingarm, it can't swing. Gotta have an inner spacing sleeve to carry the clamping force, leaving the swingarm free to move. - - -

Hi 2Many,
Yeah, that's why I said use a nylok. Just tighten until the swingarm has the recommended end float.
Mind you, I did not consider the need to stiffen the frame by locking the sides together.
Pity the bearing sleeve almost always works loose over time.
OK then, back to Yamaha's design obsession, the shoulder bolt.
(Ever notice how many of them there are on an XS650? Even the stock throughbolt?)
Neck the single fat throughbolt's threaded end down to 16mm and reef it up solid.
 
... Yamaha's design obsession, the shoulder bolt.

Neck the single fat throughbolt's threaded end down to 16mm and reef it up solid.

I like the idea of a threaded/shouldered, heat-treated, hardened, polished pivot shaft 'reefed' up solid into a threaded section of one side of the frame. That's a much better lock to the frame than a pinched thin-wall bushing.

Now, how to lock-in the other end to the other side of the frame, as solidly as that threaded end.

I'm thinking a collar/nut, threaded ID and OD. Its ID would thread onto a threaded/shouldered end of the shaft, while simultaneously threading into the frame. Torque its ID to the shaft, and locknut its OD to the frame. (Could really use a chalkboard here)...
 
Ok, wait, amend that.

Shoulder and thread both ends of the pivot bolt.
One end threads into the frame as above, and is locked down (let's say the right side, for example).

On the left side of the frame, a hollow, smoothbored bolt (like a much larger version of the front camchain slipper barrel screw) screws into the frame, over the small OD of the protruding pivot shaft.
It's torqued into the frame, the inner surface abuts the shaft shoulder, and establishes initial swingarm sideplay clearance.

Then the pivot shaft is lock-nutted to this 'smoothbored bolt', hence locked to the frame.

Swingarm sideplay clearance is established by the shoulder spacing of this pivot shaft, plus shim washers (if needed). It may be possible to adjust sideplay by servicing just this left side.

Pictures in my head are screaming for a chalkboard. The voices are, well..., just screaming...
 
Another amendment.

Switch sides. The left side needs to be static, to preserve chain alignment.

The right side will be the service side, to accomodate swingarm endplay adjustments.
 
Design by committee, eh?
Fat pivot bolt to be a 2-piece weldment with a rectangular head with two 12mm holes through that bolt to the frame from the outside.
Also a good place to shim if needful.
 
My 'committee' kept me up last night.

Then the simplest would be a single shaft, same dims as current inner bush tube, solid, internally threaded both ends. Prefit into swingarm, install, bolt-in thru existing frame holes. Two bolts fitted to the ID of the existing frame holes.

This requires no frame mods, but puts major compression and shearforces on the threaded zone...
 
My 'committee' kept me up last night.
Then the simplest would be a single shaft, same dims as current inner bush tube, solid, internally threaded both ends. Prefit into swingarm, install, bolt-in thru existing frame holes. Two bolts fitted to the ID of the existing frame holes.
This requires no frame mods, but puts major compression and shearforces on the threaded zone...

Hi 2Many,
there we go then, just about perfect. How about plain-boring the shaft mebbe a 1/2" deep each end before the thread starts and bolts with a plain shank to match so the shear stresses are on the plain part of the bolt and the threads only take the tension?
And a single minor frame mod:- the throughbolt stop block needs to be ground off to clear the new bolt head.
Perhaps MikesXS could make a kit?
 
Fred, that's it! Grade 8 plain shank snug-fitted bolts with buried threads! Super-simple, stout, minimal frame grinding. Add 5Twin's swingarm grease nipple mod, and you just might have a winner.

Wonder if grease grooves still necessary.

Spindle thru-hole on my little Atlas is too small for this.

Still have access to that Rolls Royce machinery?
 
Hi 2many,
great, we got her aced!
Got a sleeve handy to measure the OD?
Get a length of this:-
http://wingatealloys.com/products/s...-adgroup=ppc&gclid=CIab8Y6A8b4CFXQiMgodk28Aww
If you have a roller steady for the Atlas you can chuck the one end and drill & tap the other?
Alas, I left R-R (and the UK) in 1969 and my AECL contacts stopped when the bastards laid me off and closed their machine shop.
BTW, I did the 5twin nipple job back in 1988 when I did the bronze swingarm bushing & Timken headrace upgrades.
 
Here's a thread with swingarm bushing dimensions:

http://www.xs650.com/forum/showthread.php?t=24292

As it so happens, I have a brand-new set of swingarm parts from MikesXS.

Pic #1 - These are MikesXS swingarm bushings, sleeve, and grease seals. Dimensions taken from these.

Brass bushings:
ID - 22.05 mm - (0.868")
OD - 28.05 mm - (1.104")
Len - 40.00 mm - (1.575")
Flange OD - 34.00 mm - (1.359")
Flange width - 2.50 mm - (0.098")

Pivot Tube:
ID - 16.02 mm - (0.631")
OD - 21.95 mm - (0.864")
Length - 197.13 mm - (7.761")

Pic #2 - These are dimensions of the swingarm mount bungs, as measured on an XS1B:

ID - 16.00 mm - (0.630")
Inner OD - 30.00 mm - (1.181")
Outer OD - 26.00 mm - (1.024")
Length - 39.00 mm - (1.535")

Pic #3 - View of XS1B right side, showing locknut, locking washer and locking post.

The post is recessed below bung level and its distance to the bung is sufficient to avoid the head of any proposed retension bolt.
 

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