Topic: Swing arm bearing shaft dimensions needed. Just the numbers Pls.

[Oldschoolmachinist]

I bought a 1980 cb750 DOHC swing arm on eBay. In preparation for modding to fit my K8 I removed the bearings and inspected the shaft. Really the shaft wasn't horribly worn but it was showing the first signs of indexing. Since I was going to need new bearings anyway I decided to get a new shaft as well and found a set on eBay.

Well... Everything is great except the bearing kit doesn't fit the swing arm. So obviously I have either the wrong bearing kit or the wrong swing arm. So I'm hoping someone here has shaft and bearing dimensions for the 1980 cb750K DOHC swing arm.

Many thanks in advance for to the person who has the answer.

Here are the pertinent dimensions for the DOHC swing arm. It goes without saying that old parts are subject to wear and thus measurements very somewhat.
Swing arm ID 1.219" ( 30.93 )
Bearing shaft OD .944" ( 23. 97 )
Bearing shaft ID .634" ( 16.10 )
Bearing shaft length Aprox. 9.5"

Here are the dimensions of the bearing kit bought on eBay.
Shaft bearing OD 1.0435" ( 26.50 )
Bearing shaft OD .8065" ( 20.48 )
Bearing shaft ID .599" ( 15.21 )
Shaft length Aprox. 9.687

Best regards

[Oldschoolmachinist]

Rounding things out...

That'd be 31mm and 24mm

[bryanj]

For the CB750 SOHC the maximum bore of the bush is 21.8mm and the minimum OD of the shaft is 21.4mm no spec on length

For the first 750 twin cam(K model)max bush bore 21.7mm and minimum shaft OD 21.4 again no length spec

Those are numbers from the original Honda workshop manuals

[Oldschoolmachinist]

Thank you Bryan,

Do you know if those numbers are for the bronze bearing type or the needle bearing type?

[bryanj]

For the SOHC the Plastic type(bronze was aftermarket) not sure about the Twin cam as I never done one but the picture in the manual looks like a solid top hat type bush---probably plastic as well.

In that era I don't remember any chain drive Honda having needle rollers standard

[Oldschoolmachinist]

That makes sense. It could be that I've got a later model swing arm. It was sold as 1980 but who knows for sure? In any case I can make it work.

[Oldschoolmachinist]

It looks like what I have is the swing arm from an 82 CB750 Nighthawk, rather than an 80. Looks like it'll work without much additional fuss. The bearing kit I got was an after market upgrade. I'll probably just re-ebay it.

Thanks for your help.