Topic: CB750 to CB550 Swing Arm Swap

[W00d5]

So, I understand that there may be existing threads on this one. I understand that as a human being I should search first, which is why that is what I have done. I have searched this forum and others and can't find much detail at all other than, yep they swap. I am doing a full build, frame up on a 1974 CB750K. I have already purchased (for a sweet deal) a 1974 CB550 rear swingarm which has the exact same dimension from where I have measured. So, I know they swap somewhat easily. What I am not solid on is the 750 wheel on the 550 swing arm. I intended to use the wheel that came off the bike originally, sprockets included. Several questions I have below are what is keeping me uneasy at this moment as I have not gotten to the point of mock-up in the build to find out by trial and error.

1) Does the 750 wheel and sprocket work on the 550 swing arm without mod?
2) Is there any mods needed for the brake control rod?
3) With the longer axle to drive sprocket distance, what is the best approach to getting a longer chain?
4) I have heard bigger tires are possible with the 550 swing arm, but never details, how big of a tire (width specifically) could I use on the 550 swing arm with a 750K rear 18" rim?

I'm sure I missed something that someone will bring up. This is my first frame-up build and swap out of the swing arm like this. So, advice is welcomed. 

[754]

 Simple answer,
1.. Try it and see , i dont care what anyone says , put arm on and wheel without spacers, align wheel , take it from there. Be sure

3... 750 uses around a 100 links,  so longer arm, buy a 110 link, put it on and trim chain..

[Don R]

 I'm not sure about the swingarm but tire width is mostly determined by rim width. You can go a size over stock before the rim starts to pinch the tire and make it run on the center most of the time.  Have you checked the width between the adjusters on both swingarms? 
 

[BenelliSEI]

Curious to see how this turns out. Always liked the look of a CB550 swing arm! Good Luck and share some photos.

[seanbarney41]

I can see the 550f swingarm being able to accept a somewhat wider tire, but the 74-76k I dunno.  77-78k is it the same as an 550f swingarm?  Another thing I know is why there is little information to be found...because few guys see much benefit to using it and there are several problems.

[jonda500]

500/550 swing arms are all basically the same dimensions with only minor differences
- the later ones have a grease nipple.
- the 'F' ones have closed ends and the end plates are thinner (so use longer axle spacers) than 'K's with the removable ends.
- the 'F's rear chain guard mounting bolt hole is in the end plate instead of having a separate bracket on the arm. (the chain guard is chrome on 'F' models, plastic on 'K's.)
John

[newday777]

Welcome aboard WOOd5
You didn't really say why you were wanting to put the 550 swingarm on the 750 but from your wording I'm assuming(bad thing to do.....) you want to put on bigger tire sizes??
You know that bigger isn't always better with tires? Handling will suffer and tires will cup from too narrow a rim.
Rim width is a key factor putting on wider tires.
Another factor is the brake arm and chain guard will rub on wider tire.

http://forums.sohc4.net/index.php?topic=99207.0

http://forums.sohc4.net/index.php?topic=4248.0

Wider rims are available to put wider tires on a 750

https://cognitomoto.com/products/wide-rear-wheel-kit-cb750?variant=8109390401

[WhyNot2]

Are the 550 swing arms a direct bolt on to the 750K frame??

[kerryb]

My only experience with this is running a stock size'78 rear wheel and tire on a '77 cb550.  Everything bolted right up and worked.  I don't recall whether the axle spacers needed to be swapped too, but that will change with a wider tire probably.  The whole front end bolted up too and worked just fine.  I made the swap because someonre had fitted comstar wheels to the bike before me and I preferred the look of spokes.

[bryanj]

Dont think the 550 arm will take a tyre bigger than 750 standard, was smaller originaly

[Don R]

 If I wanted a big back tire I'd use a 750A swingarm. They have a longer axle and are wider as well as longer. Cycle X can fix you up with a wide rim.

 It's always a surprise when you see a post that's been around a while and suddenly 754 is there. RIP friend.

[Jcop.550]

Welcome! I am in the same boat as you are. Started my ‘73 cb750 build yesterday and have already acquired a cb550 swingarm.

From my research and understanding it will bolt right on to the frame. My plan is to put a the wider cognito rim to lace on to the stock 750 hub in order to get a bigger tire on. One thing to keep in mind is the sprocket offset which is included with the kit that cognito sells.

I’ll keep an eye on your build. One of us will get to it first and we can help each other out.


Sent from my iPhone using Tapatalk

[rocket johnny]

yes ..  rip frank .   he was always a breath  of fresh air

[bryanj]

I think you will have problems with wide tyre rubbing the swingarm, the 550 is longer but NOT wider

[WhyNot2]

My interest is not a wider tire, it's a lowered bike.

[HondaMan]

Why not just fit shorter shocks on the 750 arm? The one on the cover of my book is like that: it has 550-size shocks. The front fork tubes are also slid upward. The owner of that bike had a short pants inseam, something like 27 inches, and needed some assistance with holding up the tall 750.

[WhyNot2]

Why not just fit shorter shocks on the 750 arm? The one on the cover of my book is like that: it has 550-size shocks. The front fork tubes are also slid upward. The owner of that bike had a short pants inseam, something like 27 inches, and needed some assistance with holding up the tall 750.

I  have the 11 inch shorty shocks and still higher than  I like it. Forks also up in the tree, was told that isn't ok.

[bryanj]

Only not ok if you bottom out the forks

[WhyNot2]

I know it's been a while, but I just installed the 550 swingarm, and the chain is too short.

Any recommendations for new chains......this chain and sprockets, are fairly new, only about 500 or so miles on them.

I also install the brass(bronze) bushing, and wanted to replace the grease zerks, but lost confidence in doing so.

All else seems fine at this moment.

[chesterburnet111]

Strange when someone starts a thread and then never responds. I wouldn't be surprised if it's all still sitting around unassembled. After reading the thread, I never saw someone explain what benefit there would be by doing this swap.

[Shtonecb500]

The only reason I've seen is personal preference. Some people don't like the stamped steel 750 swing arm and enjoy the look of the round tube swing arm, as it matched the rest of the bike. The 550 swingers are the longest of the SOHC bikes I believe. 750 and 550 hubs are different so you cant use a 750 sprocket on a 550 hub and you'll have to modify chain and maybe sprockets.

[BenelliSEI]

I know it's been a while, but I just installed the 550 swingarm, and the chain is too short.

Any recommendations for new chains......this chain and sprockets, are fairly new, only about 500 or so miles on them.

I also install the brass(bronze) bushing, and wanted to replace the grease zerks, but lost confidence in doing so.

All else seems fine at this moment.

I replace those all the time. The originals just pull out. Grab them with a pair of vise grips and tap back. Somewhere I have a little package with the correct size drill bit and tap for a std. zerk fitting. It only takes a few minutes!

[HondaMan]

I know it's been a while, but I just installed the 550 swingarm, and the chain is too short.

Any recommendations for new chains......this chain and sprockets, are fairly new, only about 500 or so miles on them.

I also install the brass(bronze) bushing, and wanted to replace the grease zerks, but lost confidence in doing so.

All else seems fine at this moment.

I replace those all the time. The originals just pull out. Grab them with a pair of vise grips and tap back. Somewhere I have a little package with the correct size drill bit and tap for a std. zerk fitting. It only takes a few minutes!

The normal USA zerk threads are 1/4-28 size.

[WhyNot2]

Thanks for all the info.

[bryanj]

Whats wrong with m6 zerks? The rest of the bike is metric after all