Topic: mismatched parts CB750 F1 - CB750K0

[mazingerzeca]

Hello.
I'm finding new surprises on the K0 engine that I'm rebuilding. The bike is a CB750 F1 Supersport, but the engine come from a K0. But also, the final drive is from the F1 engine. I'm finding a problem with the final drive bearing (the one from the outside of the engine), because the inside of the K0 bearing is smaller than the F1 shaft, and the F1 bearing is too wide for the K0 crankcase and also doen't have the groove that the K0 crankcase uses.
The old bearing that the bike had is crap, and it is a bit wide, in fact, the oil seal was a bit off the engine.
So, these are my alternatives:
- To find a K0 final drive, but I don't know if it is the same lenght as the F1, and I don't know if it will align wiht the rear wheel sprocket. Maybe that is the reason why they left the F1 final drive. Also, I've seen that the F1 final driven gear has 56 teeth, and the K0 only has 50, and also, I don't know if it only refers to performance and fits or not, I mean if the width is the same and only changes the number of teeth (I would try to buy a final driven with the gear on it).
- To buy a new bearing which fits with the F1 final driven on the K0 engine. Probably I will not find easily one with the row machined, but I think it can be done on a machine shop. Maybe this is the easier route, but I've read somewhere that these bearings from the engine should be "high speed", or anything in particular.
- To have the F1 shaft machined to the K0 bearing size. I don't know if that wold weaken the shaft too much, maybe not, because the K0 shafts were that smaller width.
What would you do?

[70CB750]

I would start with measurements and a bearing catalog - just to see whaat your options are.

F engine final drive is out more compared to K0 - if the motorcycle had a rear disc brake.  What year F are we talking about here?

[mazingerzeca]

it is a cb750 fq 1976 and yes, it has a rear disc brake

[70CB750]

That means the final drive is out 10mm to acommodate for the disc.  Here is the difference:

http://www.cyclexchange.net/index%20pics/picture%206.JPG

courtesy of cyclexchange.

Hopefully somebody will pitch in with shaft compatibility option.

[754]

The 50or 56 tooth comes off easy its a non issue.  You way be able to find an inbetween bearing. .
With the wider bearing I have no doubt that the seal is almost out.. But if it hangs in there I would probably run it
 Grooving a bearing can be done but its tricky. Should be ok if bearing is full hard. Cutting shaft for other bearing can be a problem if its only case hardened, you may get thru the layer..or even worse.. Partly thru ..leaves an uneven surface.
 On late shafts.. Always check splines, have seen premature wear on these.

[mazingerzeca]

Hello.
Went to the machine shop, and they told me they could machine the shaft for the bearing that fits on the K0 crankcase. They didn't tell me about the hardened surface, and I didn't know that the surface was hardened, I thought that the shaft was all the same all through the diameter, so maybe machining it is not a good idea...

[mazingerzeca]

I think that I will start searching for a bearing and, if it is imposible to find one with a groove, I will have it machined, which I think it would be easier than machining the shaft. About the bearing, ¿which type of bearing should it be? I mean, about temperature, rpms and so on?