Swingarm Bushings

Twins, thanks for that. I'm going to follow the advice as it is easy to do and bushings like plenty of grease. But, the bushings will immediately wear at the tube to bushing interface creating clearance and I should think the grease will distribute through the bushing even if the only ports are the 2 factory ones. Has experience shown this is not the case and hence the additional grease path is critical? Just curious.
 
Well I am 2 flights of stairs above the shop and on crutches so I avoid going up and down too much. But I had to check the pivot bolt. I must have been blind! There is clearly a shoulder at the threads. That makes a very effective stress riser.

The more I look at this pivot design, the less impressed I become. Who said the designer must have had a bad day? I agree! It is essentially a friction or interference fit between the frame and the outer tube that depends on too many variables to assure that only the pivot tube rotates within the bushings. Surely a tang or pin or any number of methods could have affordably been implemented.
Scottie
 
I think when you assemble everything and torque it all up, you most likely wont have any play there. The inner tube is what stops the frame ears in the correct clearance. Those "ears" on the frame will deflect a few thousandths or so then stop when they hit the tube. The Mikes pivot shaft is a finer than stock thread with a nylock nut. I don't think that will be a concern. What was my concern with the part is the lack of any finish. It also had a lot of metal chips in the threads and grease drillways. I think I will trial fit it this week end. I can let you know how it fits anyway.
 
Thanks Gibson. I will look forward to how yours fits up. I am not worried about making this fit, I just think it is a poor design relying on too many variables for it to work properly. A positive capture of the pivot tube would have been easy to implement and reliance on bending the frame inward and shimming the thrust covers and simultaneously assuring the pivot tube properly hits the thrust covers to prevent the tube from rotating when the pivot bolt is tightened. Good grief!
 
Changed out the pivot bolt tonight. Fit was fine. I removed a lot of chips. These would have damaged new bushings if not thoroughly cleaned. I was able to open up the hole in the lock tab to make it work also. Pumped up with grease...
 
I got new bushings and seals (thrust covers) from Mikes. I didn't really like the fit of the bushing with my pivot tube as I thought it should be tighter. However, on checking the dimensions on the forum, I found my bearing area of my pivot tube measured 0.864" - the same as others have measured. My new bushings measured also exactly the same as that listed on this forum: ID = 0.868" and OD = 1.104". So my conclusion was there isn't a way to tighten the tube to bushing by ordering a new tube. The clearance is 0.004" and it will fill with grease, but I'd prefer to see a bushing with 0.001 to 0.002" clearance.

I pressed the new bushings in by heating my swingarm on my wood stove and freezing the bushings and using a 1/2" all thread with a little grease. Went right together, but definitely was a tight fit (as it should be).

With the swingarm re-assembled, I did a fit check into the frame to see what gap may exist between the seals and the frame boss. I measured one side by holding the SA firmly to the other side. Measured 3/32". That will divide by 2 when the SA is centered within the bosses. Should I shim this or button it up? gggGary, I sent you a PM on this.

I also carefully measured the amount the pivot tube is proud of the bushings. 0.004" and that means 0.002" on each side for the seals (thrust covers) to press against once the pivot shaft is torqued down. I was hoping for a little more, but that is what I have.

5Twins, I added the 45 deg zerk fitting to the SA, but did not drill new holes in the tube. I also put the zerk fitting 2.5" from the left side vs. in the center. I reasoned this would allow a bit more access during maintenance.

I'll post some pics after a bit. Scottie.
 
Hi Scottie,
my post #12 in this string explains what I'd do instead of Yamaha's "Designer's Hangover Monday" swingarm pivot concept.
If you are concerned that your 0.002" per side swingarm sideplay is too tight a few strokes of a large file across the bushing faces will fix it.
And yeah, the M14 ends on the stock 16mm throughbolt DO snap off.
Happened twice on my bike.
A full M16-ended throughbolt is just about a necessity.
That or good dirtbike riding skills. There's a photo someplace of the 100' black line my son left on Hwy 14 riding my bike to a standstill from 60mph with it's back wheel locked up.
 
HI Fred, thanks for the reply. I do agree the designer was having a bad day. I read a number of your posts on the forum, clearly you share your knowledge with all...hats off to you. I didn't see the one about the 100' black strip though...hard to watch that when its your son. We made a tradition of riding on New Years Day here in these mountains. Lastt year a riders son went down on black ice...nerve racking for the father. But only small damage to the bike.

On the fix for the SA, yours is certainly robust. I think part of the problem (other than a poor design) is that when the SA assembly does not mate up closely to the frame bosses, the frame has to be squeezed to apply enuf pressure to prevent the tube from rotating relative to the frame bosses. This means the frame bosses are no longer face parallel to the seals and a bending force is applied to the pivot bolt. That bolt we all know is weak due to its diameter step at the thread ends and that it is hollow at the same point. Keeping the faces of the bosses parallel to the faces of the seals will eliminate a bending force on the pivot bolt at the thread ends. I think shimming the gap is a good idea because it keeps the tightening force on the pivot bolt aligned with the centerline of the pivot bolt. My guess is that's what has caused the many failures of the pivot bolt.
 
Hey TwoMany, no we don't know the boss faces were intended to be parallel. Except, I would assume, when all is fitted together. Did the engineers design a jig that held the frame such that it achieved alignment only when fastened together? Seems unlikely, but who knows? Could the assembly line hold such tolerances? Seems very unlikely given the quality of welds I observe. I do believe the intent would have been to have tension only on the pivot bolt without any shear, but who knows.
Lyman77.jpg


Photos coming .
 
:wink2: I like the way you think. Machine bushings are available in many thicknesses, to take up slop. I've used them a time or two when the frame was wider than I was comfortable trying to squeeze in, note how close the lower frame cross bar is to the swing arm bolt. If the frame swing arm clearance is shimmed to start with you don't need to go all gorilla on the nut to keep the bush from rotating on the pivot shaft.

IMHO this is an area where low cost won out over proper design. Then again the design is typical of it's era. Many modern swing arms run in tapered rollers with threaded take up collars.....

Scottie said:
HI Fred, thanks for the reply. I do agree the designer was having a bad day. I read a number of your posts on the forum, clearly you share your knowledge with all...hats off to you. I didn't see the one about the 100' black strip though...hard to watch that when its your son. We made a tradition of riding on New Years Day here in these mountains. Lastt year a riders son went down on black ice...nerve racking for the father. But only small damage to the bike.

On the fix for the SA, yours is certainly robust. I think part of the problem (other than a poor design) is that when the SA assembly does not mate up closely to the frame bosses, the frame has to be squeezed to apply enuf pressure to prevent the tube from rotating relative to the frame bosses. This means the frame bosses are no longer face parallel to the seals and a bending force is applied to the pivot bolt. That bolt we all know is weak due to its diameter step at the thread ends and that it is hollow at the same point. Keeping the faces of the bosses parallel to the faces of the seals will eliminate a bending force on the pivot bolt at the thread ends. I think shimming the gap is a good idea because it keeps the tightening force on the pivot bolt aligned with the centerline of the pivot bolt. My guess is that's what has caused the many failures of the pivot bolt.
Click to expand...
 
Here are some pics of the SwingArm with the new bushings and grease nipple and as the SA sits in the frame.


The Pivot tube is 0.004" proud of the bushing with the other side held flush. That's 0.002" on each side; exactly the same as with the original bushings.


the Gap between the frame bosses and the SwingArm seal faces is about 3/32". this is not a very accurate measurement as I just held the SA firm to one boss and observed the gap on the other side...sort of an estimate really.
 
Right Gary. The lower frame member is a rigid structure and bringing the SA bosses closer together that what they are at rest is inducing a bending force on the frame that is resisted by the lower frame member...over a very short moment arm (from the lower member to the bosses). It would be nice to know what the factory considered an acceptable gap as any gap is going to add a force to the pivot bolt than what there would be if there was a "0" gap. Too much thinking on my part, I know. It is a personality flaw. My wife has to live with it every day. :)
 
machine bushings to take out the clearance are often as close as the hardware store. Fred called the pivot 16mm but I was kind of thinking it's 17mm?? anyways 5/8" bushings would do the deed. maybe with a touch of ID filing needed. really you could face file a metric washer to the needed thickness also. Hint stainless steel washers tend to be thinner than plain steel washers. Two equal shims on each side, probably not necessary.
 
I think I would a single 5/8" steel washer would be right in range.

21/32 1-5/16 0.095 why not add one?
 
Scottie, factory spec for max side play is .020". Gary's shot was taken without the torque plate/grease seal in place and at 3/32" he's still within spec.

Right, flex at the swingarm pivot can be a problem under race conditions. The first thing to do is to find out if you will have a problem at your most aggressive performance. It's a simple test: Pick a nice sweeper, heel the scoot way over on the brakes. If the bike tries to stand up when you release the binders, you have a problem with frame flex, and on this frame, you're right--the first area to address is the swingarm and pivot.

The swingarm itself is wimpy, but you know the fixes for that. If you brace or replace and the bike still stands up on you, it's time to brace the frame. Let me be clear about this. I like to pitch 'em over and I'm a bit better than average at it, but I've never needed frame bracing on a late (74 and later) frame. The simplest fix for this area came from former road racer Dwayne Burge, who used to operate 650 Central for Michael Morse. Dwayne's solution is low tech and highly effective: he welded a length of flat steel bar stock behind the motor, right across the pressed steel elements that tie the frame together and house the pivot.
 
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So, thanks to All for this dialogue and great advice. Nice to have expertise to call upon. Thank you!

Griz, I don't see Gary's pic in my thread. If you are referring to the SA pic about 9 posts up, that is mine and the Thrust Covers (seals) are in place. That is the 3/32" measurement I made. 3/32" = 0.094" or more than 3Xs the 0.020" tolerance....thanks for that. With that in mind, I noted that the old Thrust Covers are stainless steel and if one removes the old rubber, a nice "spacer" emerges. These are 0.039" in thickness and they fit nicely over the frame boss with their cupped edges facing the boss. I've cleaned them up on my wire wheel.

An executive decision has been made! I am going to use these two seals without their rubber over each boss. They will back to the new seals and that should make a pretty good interface with the right 17mm hole for the pivot bolt to slide through.This will leave me about 0.026" (less than 1/32") as the gap...assuming I can fit them in, if not, I'll use at least one. I thought about removing the cupped edge, but I can see no advantage and the cupping makes the "shim" stiffer.

I noted that my old seals have a wear pattern indicating they have been rotating relative to the bosses. That is not how it should work as the pivot bolt pinches the seals onto the Pivot Tube and it will do so with my shims too. So the seals should not move relative to the frame; the bushings (and hence the SA) should rotate relative to the seals. The seals (Thrust Covers), Pivot Tube, and the Pivot Bolt should be fixed to the frame.

I will post photos later. Note the Honda Moly 60 grease I'm using. Good stuff for sliding components.

Griz, I am interested in the handling comments. But I'll have to save that for another day!
 

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