Topic: Front end compatibility - cb650 and cb750

[MTNman]

Hey guys,

I have the opportunity tomorrow to pick up a 1982 CB750F front end.

Will it bolt on to my 1980 CB650C frame?

Thanks

[MTNman]

Okay, so I’ll add in a few details.

I have a 1980 CB650C and I want to swap out to a 1982 CB750K SuperSport front end.

I have the opportunity to buy an entire front end from the CB750K, triple tree, gauges, tire, fender, stem, everything.

Can I mount the 750 part to my chassis? Is it the same size?

Thanks

[grcamna2]

The steering bearings are a different size between the two bikes;the good news is you can still swap the 82' CB750 SS complete front end onto your CB650(modify/swap the steerer tube)with a few optional choices.
I'll now let the other members here who know more about this procedure add to this thread.

[MTNman]

The steering bearings are a different size between the two bikes;the good news is you can still swap the 82' CB750 SS complete front end onto your CB650(modify/swap the steerer tube)with a few optional choices.
I'll now let the other members here who know more about this procedure add to this thread.

That helps a lot, thanks

[grcamna2]

The steering bearings are a different size between the two bikes;the good news is you can still swap the 82' CB750 SS complete front end onto your CB650(modify/swap the steerer tube)with a few optional choices.
I'll now let the other members here who know more about this procedure add to this thread.

That helps a lot, thanks

The one member I know of who I imagine knows how to get the correct steering bearings,etc. to accomplish this swap is member 'Alan F.' and I think it will help if you get in touch with him;send him a PM.
He has a link at the bottom of his member info that has some helpful swap information.

[Alan F.]

Thanks for the vote of confidence Bill, I'll share a few resources, encouraging facts and sticky parts that can be overcome.

82 CB750SS front end will work, if you think it's a good deal get it. Your 650 has 35mm diameter fork tubes, the chrome part. CB750s of all flavors had 35mm fork tubes from 1969 to 1980, 81 & 82 had 37mm fork tubes.
Refer to this list, it's all over the Internet, just search Jap Bike Diameter List and you'll find it in several places.
http://www.clubchopper.com/forums/metric-chopper-talk/77043-jap-bikes-fork-tube-sizes-neck-bearings-axle-diameters.html
It has axle diameters, steering bearing sizes and fork tube diameters.
You'll find Honda CB650 (79-82), CB650C (80-81), CB650SC (82-85) all use:
Upper: 26 x 48.5 x 15.2
Lower: 30 x 50 x 14.4

While Honda CB750C/F/K (80-82)
Notice this list may be imperfect...
Use:
Upper: 26 x 47 x 15
Lower: 30 x 55 x 17

OK, that leaves you with 2 options.
Grind off the weld and press the steering stems out of the 2 lower triples, swap your 650 stem into the 750 triple and weld it in place. This allows use of stock size 650 bearings.

Or go to https://www.allballsracing.com/forkconversion/
Select CB650 and scroll down to 1982 CB750 SS and buy some bearings that'll adapt THE 1982 CB750SS stem to your CB650 frame neck.

I don't know if a 650 frame neck has the same height as an 82 CB750SS frame neck, there may be differences to work around, or they may be the same. The 82 CB750SS steering stem may be too long, I don't have that info.

The 82 CB750SS forks may be longer than the 650 forks, you may need to raise the fork tubes in the triples to get back to stock 650 geometry. Different, shorter fork tubes and shorter preload spacers will alter the 750 forks down to 650 fork length if needed, save that for last.

You'll also have to figure out some steering stops to keep your handlebars from hitting the tank, daunting but pretty easy in practice, you can weld in New ones, drill and tap the old ones for adjustment or drill and tap your lower triple and add some bolts to do the job. Search around for ideas, it's been done many ways.


My Google page is now lost thanks to Google changing their stuff, I've still got all of the documents somewhere. Maybe someone backed it up and it's still out there.

That was easy: https://ariesmotorcycles.com/list-of-motorcycle-reference-documents/

[grcamna2]

I appreciate you Alan F. !