MikesXS Needle Bearing Swing Arm Kit? Dec 29, 2011 18:50:44 GMT -5
Post by Burns on Dec 29, 2011 18:50:44 GMT -5
WARNING: KINDA LONG
My re-assembly starts at zero (everything off) since I'm putting things back together after their trip to the powder-coater.
Like everything else related to my perpetual but less-than-professional tinkering with this motorcycle, this task has been educational. What figured to be a straight bolt-it-back-together operation sent me on yet another information gathering quest.
As always, all XS650 roads lead to this Garage.
This particular search started when I bolted every thing back-up and noticed that the swing arm would bind as the pivot shaft nut was torqued down; something that is not noticable with the shocks mounted.
I had Mikes brass bushings in that swing arm. Inspection revealed that the flanges of those bushings were flush with the center-tube (a.k.a. "bush center", item 2, Fig 4.5, pg. 98 Haynes 1993 manual).
Since the flanges of the bushings stuck out further than anything else in the swingarm assemble they bottomed against the inner grease caps and frame members when the pivot bolt pulled those frame members in.
The bushings are a press-fit, so functionally they are the ends of the swing arm itself and when they bottom against the frame they bind the entire assembly and the grease caps become de facto bushings
As Hank Hill would say, "that's just not right."
There is a fair amount of confusion in posts regarding swingarm mounting generally. Not everyone who has posted on the topic understands that the center tube is designed as the "pinch point" (with the grease caps acting as washers abutting the frame itself). The tube is held static when the frame members are pulled together by the pivot bolt.
Also, many do not understand that the factory shims (if you had any in your stock grease caps in the first place) are not intended/designed to take up any of that "pinch" space. They do not affect the distance from the frame to the outside of the grease cap (i.e. the end of the swing arm assembly). They effect only the distance from the flange of the bushing to the inside of the grease cap. What function they serve is beyond my comprehension.
Well, bottom line is the tube has to protrude above the bushing surface and this one doesn't.
Ok, located the bind. But what was the problem?
I suspect that a batch of mikes bushings are too long. Generally speaking, tolerances are not his historical strong suit as anyone with one of his two-lobe points cams will attest.
My word of warning to anybody putting brass bushings in (other than don't) is to be sure that the center tube protrudes from the bushing flange surfaces enough to give you something to pinch between the grease caps in the frame.
I've read some other posts that suggest that powder-coating can be a culprit sometimes, but in my case there was no powder-coating on the surfaces of the swing arm fork that touch the bushings. There was just too much brass.
BTW that tube was frozen to the brass bushings and had to be driven out.
I knocked out the bushings, ordered the needle-bearing kit/new pivot bolt/zerks, and started looking for assembly instructions.
Which stalled here at: two on each side " install them in the right position."
Any clarification on 'right position" would be most appreciated.
p.s. If the kit comes and its center bearing is shorter than the swing arm is wide, I may have to eat all these words and my understanding of how this stuff all fits together will have to enter its next phase. I'll be back.
Please correct anything that I have wrong. I live by the motto: It ain't what you don't know that gets you in trouble, it is what you do know that just ain't so.
Happy New Year