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Will a 79 swingarm fit my 70 frame

markm

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I started another thread and got no responses and I looked at the title and was not what I thought I wrote, so I made a new thread with different title hoping I can squeeze a knowledgeable reply, If someone can delete my earlier post Id appreciate it.


Part of my goal of my build is to lower the total bike. I was reading that a 1979 cb750 swing arm is 2 inches longer than sohc model and is direct fit for the earlier years but no models were given. I have a 1970k frame and would like to know which 1979 cb750 swing are is the direct fit part. Any information will be appreciated. thanks
 
If anything you'll need the K one as the F one will not have a brake drum rod attachment point, it has a disc back there. '79 has plastic bushings, '80 has needle bearings and thinking the swing axle gets a little bigger with them. Only two models that year.

I for one do NOT have direct knowledge of any interchange there.
 
I copied this post;
A 79 CB 750 swing arm is a straight swap, and gives about two inches. The 80-83 swing arm can be used buy drilling the mounting holes in the frame out to 5/8 inch, and triming 1/4 inch off each side of the swing arm where it attaches to the frame.
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And this;
But that is DOHC. However it is a one year only swing arm. You could swap it with an older uglier square, ribbed one off a 77-78, or an even uglier, and shorter one off a 69-76. These will all be bolt on. Now if you want to go to some work, you can swap on an 80-83 swing arm that will look just like the 79 swing arm. You would need to cut 1/4 inch off each side of the swing arm, and the bushing inside. Then drill out the mounting holes to 5/8 inch. Also you would need to cut down the bolt, or make spacers.
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I bought a 79 750k swing arm. At least it was listed as such. Was hoping for a straight swap. No such luck. I must have been sold something other that what it was listed or folks are mistaken about straight swap.
Well the one I ended up with has the same axle size but it is wider over all.We had to take a quarter inch off both sides to make it work and the spacer that is inside the swing arm. And it is wider back where the rear axle goes also.
I will have to make some spacers for the axle. If anyone has done this and remembers the length of the spacers please let me know. I will need one on both sides.
The only good news it seems is that it is longer by 2 inches and also the mounting of the lower shock bolt is 3 inches farther to the rear that my stock 70 swing arm shock mount holes. So it does do what I need it to do. I’m not getting rid of the stock parts at this time just in case.
 
The '79 is only 1.5" longer than a '78 750K swing arm (which is a direct bolt on) and does have to be trimmed 1/4" off each side of the frame pivot. After that you can use your stock bolt. As far as spacers, use the spacers from a '78 750K. The thicker one on the drive side.
The '80+ is 2" longer and has to be trimmed the same way as the '79 BUT the frame has to be drilled out to accommodate the thicker bolt. Not a good option IMO.
I also believe (but not sure) the bolt needs to be shortened as well.
Good luck.
 
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How did the swap work out for you? I just bought a 79 swing arm for my 76 F model. Reading the forums, some guys say take a 1/4" off both sides, other guys say to take it all off the one side....
 
You need to remove 1/4" from both sides. I laid my completely stripped stock swing arm on cardboard on the floor with the very back side against a stable straight edge. I then marked where the edges of the rear arm was on the card board. I then lined up my laser (I got it for $60 to align my Jeep) to focus on the very edge of the pivot case. I made sure the laser beam was square with the back straight edge. I then removed the swing arm and replaced it with the '79. It was dead on 1/4". I thought the other side would be different just eyeballing it but when I lined up the other side it was 1/4" as well.
Good luck.
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Awesome. My biggest concern was not having the swing arm centered on the bike. But I’ll take your word for it….bike looks great by the way. The 79 swing arm looks much better.
 
Awesome. My biggest concern was not having the swing arm centered on the bike. But I’ll take your word for it….bike looks great by the way. The 79 swing arm looks much better.
You definitely want it centered. Otherwise you will not have a centered tire and it will track funny not to mention chain alignment.
 
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