Author Topic: CB750K 1978 - Swingarm & Bushings (Read 4024 times)

kixbox · « **on:** July 10, 2018, 07:57:11 AM »

Hi -

I did the good deed and took out the swingarm to inspect/re-grease. I noticed uncomfortable weird things happen during turns on a few rides. Felt I was going to lose the tail (mostly on right turns).

- replaced grease zerk (good there)
- pulled out old plastic (original) bushings - they popped right out w a socket and a extension rod - no force. Can be pressed back in easily. They need replacement. I ordered the bronze ones online (should be arriving in a week or so).

Where I am hoping to get some help is ‘how’ to put it all back together and reassemble without damaging the collar or the bushings.

Saw online vids and posts on here, but they are not specific enough for an amateur first timer. I recognize this could be a super simple job but I am no pro

and def slow).

Here is what I gathered so far:
- first, press bushings (both sides)
- second, insert collar (how?? it seems that I’d damage the collar if I force it in - this is my biggest mental block).
- third, place end dust caps, then bolt and torque. Should I replace the nut? Mine seems fine, but think I can order one.

I know the above seems soo basic, but feel monumental to me. I am gaining confidence as I press forward with my restoration. This one is so important to the overall bike that I don’t want to mess it up.

Thanks so much

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madmtnmotors · « **Reply #1 on:** July 10, 2018, 09:15:37 AM »

The OD of the collar is supposed to fit the ID of the bushing.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #2 on:** July 10, 2018, 09:58:32 AM »

Put the new bushings in your freezer overnight.

kixbox · « **Reply #3 on:** July 10, 2018, 10:07:43 AM »

I made the measurements and will retake again when the new bushings arrive.

Good idea to freeze before assembly.

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bryanj · « **Reply #4 on:** July 10, 2018, 02:43:46 PM »

The collar needs to be a good fit in the bushings and, in fact, frequently wears more than the bushes but is an expensive part.

The collar is trapped in the frame by the bolt and nut being tightened and does not turn, replaced lots of bushes and collars but never changed a bolt or nut---unless they were "Lost"!!!

kixbox · « **Reply #5 on:** July 10, 2018, 02:58:16 PM »

Quote from: bryanj on July 10, 2018, 02:43:46 PM

The collar needs to be a good fit in the bushings and, in fact, frequently wears more than the bushes but is an expensive part.

The collar is trapped in the frame by the bolt and nut being tightened and does not turn, replaced lots of bushes and collars but never changed a bolt or nut---unless they were "Lost"!!!

Awesome. I will use the same but/bolt combo.

In terms of collar wear, to my eye, it looks fine. I will make sure it’s a good fit.

Thanks

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kixbox · « **Reply #6 on:** July 21, 2018, 10:12:18 AM »

Gents - mission accomplished. I pressed in the bronze bushing (wasn’t a big hassle). It took some force - but too my time. Thanks for the tips.

Now I have a second problem: how the heck do I insert the collar into the new pressed in bushings? Seems like an impossible task without damaging both the collars and the bushings. Any advise?

Did I do it wrong?

I feel stuck at every corner with this swingarm. Your help is greatly appreciated.

Kal

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seanbarney41 · « **Reply #7 on:** July 21, 2018, 11:10:11 AM »

that collar looks pretty worn, start looking for a new one, grease it up and it should slide right in by hand. If it is galled or has burrs, you gotta fix that

madmtnmotors · « **Reply #8 on:** July 21, 2018, 11:14:05 AM »

The collar is supposed to fit inside the bushing. If the I.D. of the bushing is too small then it will need to be reamed or honed to fit. This is somewhat common depending on the supplier of the bushing. Some fit right out of the box, while others require the extra fitment step.

kixbox · « **Reply #9 on:** July 21, 2018, 11:24:21 AM »

Thank for this!! And I thought it looked worn as well. On the look out for another one for sure.

@madmtnmotors, I like the approach you are proposing. I have never honed anything before. Is that a specialty job that have to be done by someone or can I do it at home.

I took some measurements:
- ID of Bushings: 21.2mm
- OD of Collars: 21.4mm

I have to hone the bushings by 0.2mm - is that a big deal? And will it affect the integrity of the bushings/swingarm properties?

Thanks again. I am a bit more at ease now. Though I don’t know what it take to hone something - off to YouTube.

Kal

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madmtnmotors · « **Reply #10 on:** July 21, 2018, 11:29:57 AM »

Automotive machine shops can usually do it for a reasonable price. Many are experienced in reaming suspension bushings for things like king pin bushings for Ford twin I-beam suspensions and similar.

seanbarney41 · « **Reply #11 on:** July 21, 2018, 12:09:58 PM »

Make sure your collar is not egg shaped before deciding on bushing dimensions

kixbox · « **Reply #12 on:** July 21, 2018, 12:37:16 PM »

Will def do. Thanks again.

I have to tell you, I’m kind of pissed off that the fit is not right - sold under the pretext that it’s a perfect fit (this is who makes them). I needed to get this off my chest. I’m equally mad at myself for not measuring the fitment before I pressed them in. That said, I am keeping an open mind and can’t complain as I’m about to learn a new skill - honing.

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70CB750 · « **Reply #13 on:** July 21, 2018, 01:31:08 PM »

How much is the difference, any way to measure it?

kixbox · « **Reply #14 on:** July 21, 2018, 01:32:04 PM »

The diff is 0.2mm

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70CB750 · « **Reply #15 on:** July 21, 2018, 01:35:14 PM »

Best bet is to find a shop and have it reamed to fit.

But the collar looks worn out, maybe you want to find a better collar first. Message Bill Benton, I am sure he has some.

kixbox · « **Reply #16 on:** July 21, 2018, 01:53:54 PM »

Thanks man.

Stupid question: is reamed the same as honed?

Thanks for the lead on where to find a replacement - agree it looks worn out.

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70CB750 · « **Reply #17 on:** July 21, 2018, 03:04:44 PM »

Honing is more like polishing while reaming is more precise machining of the hole using a reamer that has specific precise diameter.

madmtnmotors · « **Reply #18 on:** July 21, 2018, 03:54:26 PM »

Quote from: 70CB750 on July 21, 2018, 03:04:44 PM

Honing is more like polishing while reaming is more precise machining of the hole using a reamer that has specific precise diameter.

+1

Reaming will be more accurate and better aligned. This is a common and relatively inexpensive procedure for an experienced and knowledgeable machine shop.

754 · « **Reply #19 on:** July 21, 2018, 10:41:10 PM »

First off , you got nothing to lose by trying to polish the shaft down to fit the bushings.
Will think up a method to do this.
By the time you take .2 mm off it can only look better.
In my mind I would rather have to ream or hone to fit, than use a pre fit one that ends up loose due to shaft wear.

Reaming and honing both have their own advantages.
For example if you have slight misalignment, you can often correct it by reaming. I have used an expanding reamer to fit these. Small cuts and many of them. An expanding reamer is fairly cheap, and can be done at home.
Honing is a bit more involved.

trigger · « **Reply #20 on:** July 21, 2018, 11:32:29 PM »

Quote from: kixbox on July 21, 2018, 12:37:16 PM

Will def do. Thanks again.

I have to tell you, I’m kind of pissed off that the fit is not right - sold under the pretext that it’s a perfect fit (this is who makes them). I needed to get this off my chest. I’m equally mad at myself for not measuring the fitment before I pressed them in. That said, I am keeping an open mind and can’t complain as I’m about to learn a new skill - honing.

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I have sold and fitted 100's of those bushes over the years with no problems, never had to ream any. These are top quality bronze bushes from Germany. As said before, make sure the collar is in good condition.

kixbox · « **Reply #21 on:** July 22, 2018, 03:35:18 AM »

Thanks all and for validating the brand and you experience.

Here is roughly my plan:
- find better collar and try to fit that in
- if no resolution, then I am going to attempt to hone/ream
- if nothing working, popping them out (if that is even possible) and starting from scratch again w new bushings.

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kixbox · « **Reply #22 on:** July 22, 2018, 04:01:01 AM »

Quote from: calj737 on July 22, 2018, 03:53:12 AM

Not to kick a dead horse, but, the measurement you took of your collar is likely where the delta is, not the bushing. Wear on your collar can easily account for an out-of-round dimension, galling, etc.

Before you ream that bushing, find someone with a lathe and chuck up the collar. Have them barely turn the surface to clean it up and reduce its OD. Take the swing arm with you to test for fitment. When you get the fit correct, mark the end and repeat with the opposite end.

If you're not using micrometers, your measurements are questionable.

That is definitely a good first step to make sure I’m starting off w the right collar dimensions.

I am using an electronic micrometer but it’s one of the cheap ones and not sure if it is accurate. So yes, having a pro help here is not a bad call.

With this groups help, we will bring this one to the finish line, dead or alive haha

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bryanj · « **Reply #23 on:** July 22, 2018, 04:49:34 AM »

Said it before, the pin wears more than the bushes

trigger · « **Reply #24 on:** July 22, 2018, 05:51:56 AM »

The ID of the bush is 21.50 and they fit perfectly to the collar, Some pic's

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Author Topic: CB750K 1978 - Swingarm & Bushings (Read 4024 times)