Topic: Swing Arm Install Tightness CB750K1

[pjandrew99]

So, I am installing a 72-76 CB750 swing arm into a K1. The old swing arm was extended and a bit rough.
Put the bronze bushings in and proceeded to install the arm. Real tough to get in but installed it. Unfortunately it was very stiff so I took it back out. Filed down the top hat bushings a bit and installed. Tough to get in so I pulled it out and loosened both rear motor mounts. Went in much better. Tightened up the swing arm bolt with the motor mounts loose and still stiff. Loosened the swing arm bolt and tightened the upper motor mount first. It was stiff after just tightening the upper motor mount.
As I understand it, arm should fall on its own weight. This is not even close to that.
Any suggestions are very appreciated.

[bryanj]

Have you pumped it full of grease?
Are the end caps fitted?
Does the collar protrude slightly from the bronze bushes?

[Kenzo1979]

Have you pumped it full of grease?
Are the end caps fitted?
Does the collar protrude slightly from the bronze bushes?

Endcaps, that’s what I was thinking.  Definitely grease too!

[pjandrew99]

Have you pumped it full of grease?
Are the end caps fitted?
Does the collar protrude slightly from the bronze bushes?

No, its greased but not pumped full of grease. I'll do that.
The end caps are on and I believe as far as they can go. Not sure what you mean by fitted.
Yes, collar does protrude slightly but very slightly.
Thanks!

[pjandrew99]

Caps

[Alan F.]

The collar should be what the frame is clamping on, imagine it as the center race of a wheel bearing.

[pjandrew99]

The collar should be what the frame is clamping on, imagine it as the center race of a wheel bearing.

It does but it is very very slight. Wondering if I should file a bit more off the bushings.

[BenelliSEI]

The main tube inside has to stick out enough so the washers are not dragging in the swing arm. The last time I used aftermarket brass bushings, I had to take off about 1/2 of the end rim portion(of the bushings) for it to swing properly...... I think they make them a bit thick for fear of the part snapping off.

[bryanj]

When you tighten the bolt through the collar it should trap the thin end caps against the end of the collar and the whole endcap collar assembly in the frame, the distance between the inside of the caps should be fractionally more than the width on the swing arm and brass bushes.
If you had the arm powder coated and did not remove it from the ends before fitting new bushes the assembly will be slightly too wide.

[JamesH]

So, I am installing a 72-76 CB750 swing arm into a K1. The old swing arm was extended and a bit rough.
Put the bronze bushings in and proceeded to install the arm. Real tough to get in but installed it. Unfortunately it was very stiff so I took it back out. Filed down the top hat bushings a bit and installed. Tough to get in so I pulled it out and loosened both rear motor mounts. Went in much better. Tightened up the swing arm bolt with the motor mounts loose and still stiff. Loosened the swing arm bolt and tightened the upper motor mount first. It was stiff after just tightening the upper motor mount.
As I understand it, arm should fall on its own weight. This is not even close to that.
Any suggestions are very appreciated.

Has the swingarm been painted / powder coated? You need a bare metal finish where the top hat of the bronze bushings ‘seat’ on the outer face of the swingarm.


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[pjandrew99]

Took a little bit more off the bushings. No improvement. I believe I have room to take a little more off but getting close to making it too thin.
I'm using Mobil 1 grease. Not sure that makes any difference. It moves fine until I start to tighten things up.
Does it matter at all how I tighten everything up?  In other words, tighten up the motor mounts first or in some kind of specific sequence?
Never checked the old swing arm movement before I took off. For all I know that was tight too. Not sure. I measured the old swing arm and collar and they match up fine.
I'm grasping at straws at this point.
Appreciate all the help.

[BenelliSEI]

As stated. The centre tube needs to stick out enough from the busing “top hat” rim. When you tighten the centre through bolt the two washers at the end and the centre tube get locked tight to the frame. The swing arm and bushings need to be free to swing on the centre tube......

[seanbarney41]

Make sure the end cap's inside are not interfering with the swingarm.  I have seen some that fit too tight.  Especially when parts are getting swapped around.

[pjandrew99]

Make sure the end cap's inside are not interfering with the swingarm.  I have seen some that fit too tight.  Especially when parts are getting swapped around.

That is a possibly. When I rotate the cap on the bushing/swing arm it does tend to slightly bind.  In that case, modify the end cap so it acts more like a washer than a cap? Thanks!

[pjandrew99]

There are also some welds on the swing arm that may be interfering with the movement of the end cap. I could try filing that as well. Its very slight but could make a difference.

[Tracksnblades1]

Does your engine’s rear mount bolt hole bosses look like they’ve been ran loose or over tightened?

One could put a .005 or .010 precision shim washer in between the motor and frame to get the mount bolts to the required torque without impeding the swing arm movement. You could try removing them once everything takes a wear set…

Some large machinery service manuals recommends rapping the shafts with a deadblow hammer to seat pressed on  preloaded large bearings and shims prior to checking the rolling torque of the assembly.

[Henning]

Are you using the "top hat" style bushings? In that case you don't use the end caps. It came from the factory with straight bushings (and the end caps).

[pjandrew99]

Does your engine’s rear mount bolt hole bosses look like they’ve been ran loose or over tightened?

One could put a .005 or .010 precision shim washer in between the motor and frame to get the mount bolts to the required torque without impeding the swing arm movement. You could try removing them once everything takes a wear set…

Some large machinery service manuals recommends rapping the shafts with a deadblow hammer to seat pressed on  preloaded large bearings and shims prior to checking the rolling torque of the assembly.

From what I can tell the rear mounts are good but I will check into that. If I tighten the swing arm nut with the motor mounts loose the swing arm tightens up and becomes stiff.  Will that eliminate the motor mounts as a potential issue?

[pjandrew99]

Are you using the "top hat" style bushings? In that case you don't use the end caps. It came from the factory with straight bushings (and the end caps).

Yes, they are top hat bushings. The end caps I am referring to are the ones in the pictures I posted. Thanks

[xhevi]

my old swing arm bolt had a slight bend that made it stiff.

[pjandrew99]

my old swing arm bolt had a slight bend that made it stiff.

I'll check it out. Thanks!

[Kenzo1979]

Are you using the "top hat" style bushings? In that case you don't use the end caps. It came from the factory with straight bushings (and the end caps).

I would imagine you still need the end caps, they are just the dust covers.  The top hat style bushing probably just omits the thrust bushing.

[pjandrew99]

So, I cleaned up the caps and made sure they rotated on the bushings without any binding. I also took a bit more off the bushings. Put it back together with 40lbs of torque and no improvement.

Does anyone have a picture of how thin you can go on these bushings? I think I'm down to about half of what it was.

I noticed when I was greasing it up through the zerks on each side of the bolt that eventually grease was coming out between the cap and bushing. Is that normal?

Next step is to check out the swing arm bolt for straightness.

Thanks!

[Kenzo1979]

Can you post pictures like your previous ones but without the end caps on so we can see the thickness of the brim of the top hat? Also after all the milling you did, you should also post the current  thickness of that brim (lip, whatever, seems like we’re speaking in hat talk now so I’ll just run with that analogy) in millimeters.  Did you remove the old thrust bushings from the swing arm before you put the new bushings in, if so, how does that compare to the brim of the new bushing? If you didn’t have those pieces, maybe somebody does and can measure to tell you how thick that portion is supposed to be on each end. 

[Kenzo1979]

Apparently the brim of that hat (exposed lip outside of the swingarm tube, under the end “dust” caps) should be 2mm.