Topic: CB750 engine year/model compatibility?

[macvit7906]

Starting a 1975 CB750F Supersport project.

I'm going to have to piece together much of the engine. Right now I only have the cases, crank, pistons, heads, and most of the tranny.

Wondering if engine components are compatible across all CB750 models. Do K1 parts fit into an F, etc?
Anything I should stay away from interchanging?

I've built a few bikes but this is my first CB so I'm unfamiliar with the engine component interchangeability across all the models.

Thanks!

[bryanj]

Heads, barrells and associated gasket rubber bits change so you need head and barrells from same model and gaskets to suit

[macvit7906]

Heads, barrells and associated gasket rubber bits change so you need head and barrells from same model and gaskets to suit

Thanks Bryan. Have all those already, so good there. What about pieces like shift drum and shifter pieces, valves, valve springs, cam and cam chain/holders, rocker arms? internals the same for the most part?

[Don R]

 77/78 F's have different parts, the output shaft bearings differ at some point, The 71 head is visually different but will work fine. Any real early stuff (k0) you find can be traded for newer parts. The 75/76 F and 77/78K motor was a good one, if you find one grab it. 

[bryanj]

As Don said, over the many years there were 3 different output shafts and 4 different crankcase castings plus many "in service" modifications like shift drum, clutch pack etc but if you keep complete sub assemblies together they mostly swop over. Different valves in 77 onwards that only fit in those heads and multiple different cams but they all interchange.

[macvit7906]

gotcha. Thanks guys.

I'll stay away from later year 77/78 parts to be safe.

Using this site and basically just making sure I'm grabbing the correct parts #s
http://www.hondachopper.com/engine/fiche_pages/fiche_pages.html

[PeWe]

Make sure that the outgoing shaft has the dual row bearing. Early engine had only single row.
(front sprocket shaft and just inside the big oil seal)
K6 got another clutch with outer fiber plate with wider tabs that fits its clutch basket. The basket is fastened in the shaft with a clip. Earlier has just a bigger spline washer, no groove in shaft going thru the primary hub for the clip.
EDIT: I ordered a primary hub from USA that came from a 1975 F. It was the earlier model. As you can see, no groove for clip as the later 76 /K6, F1, F2 got.
https://www.5thgearparts.com/products/1975-honda-cb750-super-sport-4?variant=1056024541

Primary hub has rubbers inside that most likely must be hard as bakelite. There are upgrade kits. CycleX has in US. There is another company in Germany that can do the job for 20€ extra. But it cost shipping to send the hub to  and from them. Total still OK. I let them replace the needle bearings inside hub too just for sure in one they did for me.
http://www.fourever-classic-parts.de/index.php?option=com_content&view=article&id=26&Itemid=31

[macvit7906]

Make sure that the outgoing shaft has the dual row bearing. Early engine had only single row.
(front sprocket shaft and just inside the big oil seal)
K6 got another clutch with outer fiber plate with wider tabs that fits its clutch basket. The basket is fastened in the shaft with a clip. Earlier has just a bigger spline washer, no groove in shaft going thru the primary hub for the clip.

Primary hub has rubbers inside that most likely must be hard as bakelite. There are upgrade kits. CycleX has in US. There is another company in Germany that can do the job for 20€ extra. But it cost shipping to send the hub to  and from them. Total still OK. I let them relace the needle bearings inside hub too just for sure in one they did for me.
http://www.fourever-classic-parts.de/index.php?option=com_content&view=article&id=26&Itemid=31

Thanks for the info. Think I have the correct output shaft already. Number 7 here? http://www.hondachopper.com/engine/fiche_pages/F0/F0-Primary_Chain-Tensioner-Kick_Gears-Ouput_Shaft.pdf

I have no wheels yet. I may get a fresh pare. Any suggestions on sizes/brands that fit nicely? I'm all ears.

[Don R]

  If you need rims and hubs you are limited by the F rear disc brake. 75,76 F are the only two factory wire wheel disc brake options. If you're talking needing just rims there are lots of options. A parts bike might be a good choice.

[macvit7906]

  If you need rims and hubs you are limited by the F rear disc brake. 75,76 F are the only two factory wire wheel disc brake options. If you're talking needing just rims there are lots of options. A parts bike might be a good choice.

Yeah still need the whole rear set up and rim. Was thinking about rear disk conversion, but like the look of the original drum.