Topic: Swing Arm Install Tightness CB750K1

[Kenzo1979]

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......

I think you need to focus on this;  And that lip thickness could be part of this.  The collar or "center tube" needs to be protruding out through the entirety of the swingarm, extending enough past those top hat brims in order for the frame to pinch on the collar, not on the bushings.  The bushings (inside) need to rotate on the collar (outside).  That collar needs to be trapped in place by the frame between the end "dust" caps.

[MCRider]

I had a swingarm once with aftermarket bushings. I had to make some shims from sheet metal to slip into the seams of the engine and frame to hold the frame at a point where the swingarm would swing.

[Kenzo1979]

Like this.

[Tracksnblades1]

Here’s a picture of the 75/76f swing arm depicting the top hat bushings (3)  a little better.

I think the members’ concerns are top hat’s outer ring thickness and od.. This Hat rim of the bushing provides the thrust bearings for side to side movement. (4) dictates the width between dust caps and prevents the caps from compressing on thrust part of the hat bushings. It’s made to pivot on (4).
Pivot bolt torque 32.5-50ftlbs.

The two rear motor mount bolts can cause some issues also if the width of the motor bolt bosses have been worn or altered. allowing those two bolts to draw the frame together farther than designed when torqued. 21-28lbft.

[pjandrew99]

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......

I think you need to focus on this;  And that lip thickness could be part of this.  The collar or "center tube" needs to be protruding out through the entirety of the swingarm, extending enough past those top hat brims in order for the frame to pinch on the collar, not on the bushings.  The bushings (inside) need to rotate on the collar (outside).  That collar needs to be trapped in place by the frame between the end "dust" caps.

This is where I am at right now. My cheap calipers are no more but the collar does protrude out of both sides although not by much. Maybe not enough?  Not sure how much more I can take off the bushings. I do understand that the collar must meet with the end caps  which fixes the collar in place allowing the swing arm/bushing to rotate around it.

I had a swingarm once with aftermarket bushings. I had to make some shims from sheet metal to slip into the seams of the engine and frame to hold the frame at a point where the swingarm would swing.

So, tighten the swing arm bolt to spec..  Then shim the upper or lower or both rear motor mounts as required

Here’s a picture of the 75/76f swing arm depicting the top hat bushings (3)  a little better.

I think the members’ concerns are top hat’s outer ring thickness and od.. This Hat rim of the bushing provides the thrust bearings for side to side movement. (4) dictates the width between dust caps and prevents the caps from compressing on thrust part of the hat bushings. It’s made to pivot on (4).
Pivot bolt torque 32.5-50ftlbs.

The two rear motor mount bolts can cause some issues also if the width of the motor bolt bosses have been worn or altered. allowing those two bolts to draw the frame together farther than designed when torqued. 21-28lbft.

until the swing arm frees up. Essentially torquing the frame to allow the swing arm to rotate freely.

Thanks!

[Tracksnblades1]

Look inside your end caps and see whether they are worn where (4) pinches everything together when the pivot bolt is torqued. Picture.

Check if end caps will seat against (4) with out touching swingarm first or od or thrust part of hat bushings.. I’d tighten it up with the bolt before placing in frame so you can identify where it’s binding when the bolt is tightened. You’ll probably need some washers..Snug first check, tighten check, torque check 😁

[Tracksnblades1]

http://forums.sohc4.net/index.php?action=dlattach;topic=189464.0;attach=456162;image

Is that satin mark a chamfer or wear mark…?

[bryanj]

Looking at those pics the od of the top hat is rubbing inside the end cap

[Tracksnblades1]

Looking at those pics the od of the top hat is rubbing inside the end cap

🎯
http://forums.sohc4.net/index.php?action=dlattach;topic=189464.0;attach=456162;image

And the paint is uniformly removed on swingarm tube in image above.  I’d like to see the end caps..

[pjandrew99]

Look inside your end caps and see whether they are worn where (4) pinches everything together when the pivot bolt is torqued. Picture.

Check if end caps will seat against (4) with out touching swingarm first or od or thrust part of hat bushings.. I’d tighten it up with the bolt before placing in frame so you can identify where it’s binding when the bolt is tightened. You’ll probably need some washers..Snug first check, tighten check, torque check 😁

Looking at those pics the od of the top hat is rubbing inside the end cap

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

Well, I think we are making progress. When I run my finger along the inside of both caps one shows some wear. An indentation where the collar meets the cap. One has wear, the other does not.
Also, rolled the swing arm bolt along a level table with a light behind it. The bolt appears to have a slight bow in it.

I'm going to order new end caps and try to find a used, straight swing arm bolt. Once I do that and if the issue persists, I'll work on shimming the motor/frame.

[pjandrew99]

Just wanted to thank everyone for all the help.
Great forum with great people!
I'll post an update after new end caps and bolt is installed.

[Henning]

  After looking at the pics and thinking about it, I stand corrected re. the use of end caps with the top hat style bushings.

I have a 750 K1. Ten years ago I replaced the collar, bushings, end caps, felt washers and thrust washers to original spec. with the straight style bushings. After assembly the swingarm was stiff to move up and down, I just tightened the nut and didn't use a torque wrench, and figured it would wear in. After maybe 10K or more miles I took it all apart for inspection and lube, and on reassembly it was just as stiff as when I first assembled it. Moral? I'm not fussed about it but it's difficult to communicate acceptably stiff to too stiff across the internet.

Yes, it can be a struggle to get the swingarm back in, even with the rear motor mounts loosened. I connect the shocks first, that keeps the swingarm level. Then a scissor jack under the front to push up, plus a mallet to wack the swingarm forward until you can get a screwdriver or whatever into the collar to guide it into place.

The PO of this particular gem of a motorcycle struggled so much to get the swingarm back in that he put the end caps on the outside of the frame 

[pjandrew99]

After looking at the pics and thinking about it, I stand corrected re. the use of end caps with the top hat style bushings.

I have a 750 K1. Ten years ago I replaced the collar, bushings, end caps, felt washers and thrust washers to original spec. with the straight style bushings. After assembly the swingarm was stiff to move up and down, I just tightened the nut and didn't use a torque wrench, and figured it would wear in. After maybe 10K or more miles I took it all apart for inspection and lube, and on reassembly it was just as stiff as when I first assembled it. Moral? I'm not fussed about it but it's difficult to communicate acceptably stiff to too stiff across the internet.

Yes, it can be a struggle to get the swingarm back in, even with the rear motor mounts loosened. I connect the shocks first, that keeps the swingarm level. Then a scissor jack under the front to push up, plus a mallet to wack the swingarm forward until you can get a screwdriver or whatever into the collar to guide it into place.

The PO of this particular gem of a motorcycle struggled so much to get the swingarm back in that he put the end caps on the outside of the frame 

LOL... I have a gem too but doubt that I'd resort to that! Although, last night I was close. Thanks for the help!

[HondaMan]

Hmmm...the collar must stick out of the ends of the bushings (the 'top hat' ends) by 0.001"-0.004". The collar compresses about 0.001"-0.002" when torqued to 17-25 ft-lbs.

Something to note, however: the bronze top-hat bushings are NOT made to smoothly rotate under the end cups like the phenolic ones did. They are going to have much more friction, so go with the lower torque number (15-17 ft-lbs) when tightening the bolt. Also: of all the flanged bushings I have measured, NONE meet the dimensions of the phenolic bushings. The outer installed height should be 2mm above the (unpainted) ends of the arm. Having a bowed bolt does not matter: it will straighten when tightened.

[pjandrew99]

Hmmm...the collar must stick out of the ends of the bushings (the 'top hat' ends) by 0.001"-0.004". The collar compresses about 0.001"-0.002" when torqued to 17-25 ft-lbs.

Something to note, however: the bronze top-hat bushings are NOT made to smoothly rotate under the end cups like the phenolic ones did. They are going to have much more friction, so go with the lower torque number (15-17 ft-lbs) when tightening the bolt. Also: of all the flanged bushings I have measured, NONE meet the dimensions of the phenolic bushings. The outer installed height should be 2mm above the (unpainted) ends of the arm. Having a bowed bolt does not matter: it will straighten when tightened.

Thanks HondaMan! I thought the spec was 40ft-lbs. I'll reduce it to 15-17ft-lbs. I ordered new end caps but I'll keep the bolt I have. Hopefully the reduced torque and the new end caps do the trick. I'll post an update as soon as I get that done. Much appreciated!

[HondaMan]

I looked back at some old notes about the bronze bushings: I was able to "fix" a set that someone had installed, but it bound tightly when he torqued the bolt down. He sent me the arm, and I sanded the flange faces down until the collar stuck out 0.002" (0.001" on each side when installed) and rounded the outer edges of those flanges with a file. This should keep them from cracking off, which the bronze ones are famous for: when they rub too tightly against the outer cups because of the sharp outer edges (and the originally too-thick flanges) they can crack right at the sharp edge where they enter the swingarm tube. Rounding off the outer edges let them rotate more easily.

[pjandrew99]

I looked back at some old notes about the bronze bushings: I was able to "fix" a set that someone had installed, but it bound tightly when he torqued the bolt down. He sent me the arm, and I sanded the flange faces down until the collar stuck out 0.002" (0.001" on each side when installed) and rounded the outer edges of those flanges with a file. This should keep them from cracking off, which the bronze ones are famous for: when they rub too tightly against the outer cups because of the sharp outer edges (and the originally too-thick flanges) they can crack right at the sharp edge where they enter the swingarm tube. Rounding off the outer edges let them rotate more easily.

Time for me to replace the cheapy caliper I tossed out. I'll check the thickness and round the edges. As soon as I get the new end caps I'll install with these modifications and update. Thanks HondaMan!

[pjandrew99]

Update: Thickness of bushing top hat looks good. Rounded out the edges. Installed the new end caps. Put swing arm on and torqued to 17ft lbs. Side note: Seems like I should add some Loctite to the swing arm bolt/nut?? Also, my self locking nut doesn't seem very self locking anymore. Time for new nut.
So, once I did the above the swing arm dropped on its own weight. Looked good. Went to tighten upper rear motor mount bolt. Tightened it up first before torqueing it down fully. Checked the swing arm and it was tight.
I suppose my next step is adding shims between the engine and frame. Is there a procedure to follow for this? What kind of shims? Based on a previous post sheet metal is good. If so, would I cut it in a horseshoe shape to slide it in around the bolt between the engine and frame?
Since tightening the top mount increased the swing arm stiffness, I assume I would tackle that first then move to the lower.
As always, appreciate the help!!!!

[BenelliSEI]

Try squeezing the ground strap between the engine and frame (usually on the outside of the frame). Make sure the frame is clean in there. That should give you some extra clearance and it looks good too.

[pjandrew99]

Will do. Thanks!

[pjandrew99]

So, really didn't have a lot of confidence that I could clean it well enough between the frame and engine to put the ground wire. However I did get a stainless washer in there which was close to the same width as the ground connector.
Tightened everything up and swing arm is still stiff.
Thinking of shimming the other side of the top engine bolt. Need to find a better way to get in there without causing any damage. Pretty good access to get to three of the four areas where the rear of the engine meets frame. Right lower looks difficult.

[HondaMan]

A word of engineering input here:
First: the battery ground lug goes between the left-side frame bolster and the engine, at the top of the engine, by the chain. This sets the proer width of the front side of this section of the frame. This thickness is important, here's why:
The frame system on this bike is a 'loaded rhombus' center strut design. In non-engineering terms: the engine's side of the frame is tighter than the swingarm's side of the frame in the middle of the frame so as to prestress the center of the whole assembly tightly. This is normal, and needed, to reduce flexing in the middle of the frame, which would give (and does) the bike a sensation of having a 'hinge' below your butt when cornering and flipping the bike side-to-side at speed. So, do NOT shim the engine side to loosen up the swingarm: that's not good, nor the right thing to do.

Normally the swingarms are stiff upon rebuild, for several hundred to a thousand miles or so. When the bikes were brand-new the swingarms did not drop under their own weight: they were quite stiff for several hundred miles. That is normal for a plain-bearing, near-interference fit.

[Don R]

   A few years ago, I bought out a guys cb750 stock that was moving and retiring, I got a few parts bikes, boxes of stuff and a lovely K4 type swingarm with new brass bushings already installed. Except it's been chromed. Yuk.
   I may take it apart to see what's been done and hopefully move the parts to my brothers one owner K4.

[pjandrew99]

A word of engineering input here:
First: the battery ground lug goes between the left-side frame bolster and the engine, at the top of the engine, by the chain. This sets the proer width of the front side of this section of the frame. This thickness is important, here's why:
The frame system on this bike is a 'loaded rhombus' center strut design. In non-engineering terms: the engine's side of the frame is tighter than the swingarm's side of the frame in the middle of the frame so as to prestress the center of the whole assembly tightly. This is normal, and needed, to reduce flexing in the middle of the frame, which would give (and does) the bike a sensation of having a 'hinge' below your butt when cornering and flipping the bike side-to-side at speed. So, do NOT shim the engine side to loosen up the swingarm: that's not good, nor the right thing to do.

Normally the swingarms are stiff upon rebuild, for several hundred to a thousand miles or so. When the bikes were brand-new the swingarms did not drop under their own weight: they were quite stiff for several hundred miles. That is normal for a plain-bearing, near-interference fit.

My ground wire is attached to the outside of the frame as shown in the picture. I placed a shim of the same width on the other side of that between the engine and the frame. So, from the factory was the ground wire where I placed the shim? This was recommended on a previous post but my concern was that I could not clean that area well enough to be confident my ground would be good. Currently, the shim takes up the space where the ground would be and the outside ground mount was functional.
Based on that and if I am reading this correctly could leave the shim and the ground where it is? Appreciate the help!

[BenelliSEI]

A word of engineering input here:
First: the battery ground lug goes between the left-side frame bolster and the engine, at the top of the engine, by the chain. This sets the proer width of the front side of this section of the frame. This thickness is important, here's why:
The frame system on this bike is a 'loaded rhombus' center strut design. In non-engineering terms: the engine's side of the frame is tighter than the swingarm's side of the frame in the middle of the frame so as to prestress the center of the whole assembly tightly. This is normal, and needed, to reduce flexing in the middle of the frame, which would give (and does) the bike a sensation of having a 'hinge' below your butt when cornering and flipping the bike side-to-side at speed. So, do NOT shim the engine side to loosen up the swingarm: that's not good, nor the right thing to do.

Normally the swingarms are stiff upon rebuild, for several hundred to a thousand miles or so. When the bikes were brand-new the swingarms did not drop under their own weight: they were quite stiff for several hundred miles. That is normal for a plain-bearing, near-interference fit.

Mark.... for clarification, when I do final assembly of my ‘69 cb750, you’re saying the ground strap from the battery should be slipped in, between the engine and the frame (upper, rear through bolt)? Thanks.