Topic: Round tube swingarms that fit the CB750K

[Mr Freeze]

Hey everyone. Looking for an answer about which round tube swingarms would fit a 1978 K frame. I got a late model '77 or '78 CB550F swingarm that fits the mounting width, but has an offset that the CB750 arm doesn't have. With my 1978 wheel and spacers, the wheel is shifted way off center. I'm thinking that's the difference in motors maybe? Anyways. I'm looking for the info on what arms fit. I'm also looking to use eye to eye shocks so if it's a Suzuki or Kawi arm that'd work too.

[Mr Freeze]

Anyone?

[seanbarney41]

probably not many have done it as the the cb750 arm is actually one of the best of the '70's jap bikes once the bushings are sorted

[calj737]

I'm with Sean on the lack of those who've made the swaps. Can you not simply make the appropriate axle spacer and re-center your wheel? Or, perhaps an offset sprocket will align the wheel to your motor?

As for Eye-Eye mounts, just knock off whats there, and weld on what you need. The modifications you're describing are pretty easy to do and would let you have exactly what you want without enormous geometry changes or milling expense from grafting in a different brand arm to your bike.

Another option would be to acquire a Seely-type arm, but that will be expensive and the shocks are still clevis on bottom.

[madmtnmotors]

Doesn't the 79' DOHC come pretty close?

[70CB750]

Doesn't the 79' DOHC come pretty close?

I think Lucky adapted 79 DOHC arm to SOHC frame.  From what I remember, he had to narrow it - not much - to fit in the frame.

[Mr Freeze]

Thing about the spacer thing is that with an offset swingarm such as the 550. It makes the wheel sit way over to the right if you are sighting the bike from the rear. I'd want measurements of a 79 DOHC swingarm before I looked for a new one so I know what I need to do to make it fit.

[seanbarney41]

Just curious...what is it about a round tube swingarm that you want?

[Mr Freeze]

I'm doing more of a swingarm chop thing with this current project and I think a round tube swingarm looks better with what I'm going for. Right now the 77 CB550F swingarm is on there, but the offset makes the wheel very off center.

[seanbarney41]

Ok, I get it now.   Tried centering the wheel with axle spacers then do what needs to be done to line up sprockets?

[Mr Freeze]

So I paired the 750 rear axle and spacers with the 550 swingarm and because the swingarm is offset, the wheel is shifted off the center line as a result.

[Mr Freeze]

See this is a '79 DOHC CB750 swingarm and already the forks look more symmetrical compared to a 550 arm.

CB750 DOHC



CB550 that's on there now.



If someone can verify that the DOHC swingarm will work with an SOHC frame ( I can shorten the width if neccessary) then my next question is bronze bushings for a DOHC swingarm and does the SOHC pivot fit. Need dimensions if possible.

[WaleFab]

I made my swing arm bushings and looked for my drawings as to the OD and shoulder thickness/dia but cant recall / find them..., but I know that the ID for the CB750 is 14mm which really is all that would matter in regards to if the shaft would fit. Could buy a OEM for the 8$ or whatever they are and measure them for the OD for the press fit...

Compare the widths of the pivot tubes that goes between the frame. If need be, get some custom swing arm bushings made up with either thinner or thicker shoulders to fit between the frame (keep in mind dust seals have to go on aswell)
Its a good time replace or install a grease nipple aswell...

Side note... do the drop out slots and axle size for wheel being used correspond?

[BPellerine]

the longer side of the pivot tube has to be trimmed to make the dohc arm fit,then it is a straight forward swap.bill

[Mr Freeze]

the longer side of the pivot tube has to be trimmed to make the dohc arm fit,then it is a straight forward swap.bill

That's the answer I was looking for. Thanks!

[Nipet1974]

the longer side of the pivot tube has to be trimmed to make the dohc arm fit,then it is a straight forward swap.bill

hi,Nipet1974 here!!i bought a 1981 cb750c DOHC swingarm for my cb750 k2 as i wanted the extended look.can you please help me out and tell me if i need to trim the pivot tube only on the right side or at both sides and if so why in every occasion and what to do exactly with thd inner bushings and seals to make it fit my frame??i would really appreciate it!! I could use the mm measurements but i guess i can work with inches too!!thank you guys!!!!

[todd.s.holloway]

See this is a '79 DOHC CB750 swingarm and already the forks look more symmetrical compared to a 550 arm.

CB750 DOHC



CB550 that's on there now.



If someone can verify that the DOHC swingarm will work with an SOHC frame ( I can shorten the width if neccessary) then my next question is bronze bushings for a DOHC swingarm and does the SOHC pivot fit. Need dimensions if possible.

What was the outcome to this? Did you use the DOHC swingarm?

I’m currently trying to make a 550 swingarm work on my 1975 cb750, with the same offset to the right issue you had. Is the only answer to get a new swingarm?

I know some big name bike builders have used the 550 swingarm on a 750


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[madmtnmotors]

I am running the DOHC 750 swingarm on my dragbike. Had to trim the tube at the pivot but don't remember how much. I seem to think I may have trimmed a little off both sides with most of the trimming being done to the long side, on the right (brake) side. Also, the DOHC 750 swingarm is about 1-1/2" to 2" longer than the SOHC 750 swingarm which will lean the shocks over a little more making the rear sit just a little lower with the same shocks.

Big name? Like, more than four syllables?