Topic: whats the difference between a F and a K frame?

[jaguar]

im building up a CR750ish cafe racer.  im useing a 76 F frame.  im tring to mount the seat right now.  i know that the "tabs" on the bottom rear of the seat and the eyelets on the rear of the frame are supose to line up(been told thats how it mounts).  but i cant slide the seat back that far because of that rear brigde on the frame.  and anyway that would be too much of a gap between the tank and the seat.   so i figure its made for a K frame.  im tring to find out if there is any other big differences between the F and K frames.  if there are not i will just cut the rear of the frame to fit but if there are maybe i will look for a K frame

[mrbreeze]

Not sure of all differences cause I'm a K kinda guy but one difference would be the F has a disc brake in the rear so should have different mounts back there. Also...the newer F's had 630 chain so they have a wider swingarm. Someone will chime in and tell you more differences......there are lots of F owners here.

[75750SS]

I believe the 75 (first F) and 76 were identicle.  Don't know about 77 and 78 models.  Here's a link to a review done on the 75:

http://www.sohc4.net/index.php?title=1975_Cycle_World_Test:_Honda_CB750F0

[jaguar]

i know that the whole bike is different.
i would like to run disc on the rear.
im looking for differences in  only the frame

[Clyde]

Differences (between a 76 F and an early K frame) I can remember are:-
-Steering head angle is different (greater, but compensated by the forks being closer to the steering head) (preferable to use F triple tree rather than K)
-Has a bracket for the rear disc brake master cylinder
-Seat mounting is totally different to the K (opposite side/one hinge)
-Seat Bridge is further back (seat cowl)
-Oil tank is different although I think the mounting points are the same
-Side cover mounts are different
-Rear engine mount is different.
-Rear fender mount points are different
-Rear tank rubber mount is in a different position (further back I think-need to check?) The tank rubber is the same
-Exhaust supports at rear are different
-has a bracket for the wiring box at the front of the frame (remove if using a K wiring harness

If you can fit the seat and tank I would stick with the F frame, especially if you want to run a rear disc. If you are running a stock rear disc, I suggest changing the rear caliper to a later F2 DOHC type. They fit perfectly and will work much better, plus you can get parts easier for them.
I also find the F handles better than the K (this should upset a few people)

Regds Clyde

[jaguar]

the rear motor mount is different?  so i cant use a K motor? 

[Clyde]

No problem interchanging motors, I meant the mounting bracket that bolts to the rear of the engine on the right hand side.
The early K's had a flat bracket that had the nuts welded on the back. The F has a similar, but different bracket that is screwed into threads already in the frame.
Sorry to cause confusion
Clyde

[jaguar]

im still thinking about how to go about this.  might be easyer to just cut the frame

[754]

By CR 750 do you mean factory raced back in 69 or 70??

Seing as they only had K frames back then, would an F frame not be a bit incorrect.. unless you consider an F discwheel/brake setup to be the hot setuip? Which was not what the CR used..

[Geeto67]

By CR 750 do you mean factory raced back in 69 or 70??

Seing as they only had K frames back then, would an F frame not be a bit incorrect.. unless you consider an F discwheel/brake setup to be the hot setuip? Which was not what the CR used..

honestly...who the F%$% cares

certainly not the people making the parts for all the different frames. Besided which honda recalled a lot of the 970 CR kits so the original stuff is pretty rare.

I don't remember the F frames being any longer than a K bike frame. In fact here in the city there are a couple of guys who have F cb750s where they have adapted K rear fenders, lights, etc and used custom seats.

remember the oil tank fill nec is supposed to be in between the tank and the seat (that is why the seat has that horseshoe shape at the front.