Topic: Front end swap..750F3 to 750K8

[zeus87]

I have roller 78' cb750f3, and wanted to swap the single disc off my K8 for the dual disc F3.  Has anyone done this? is it as easy as removing one and replacing it with another?  also my fork tubes are rusty on the F3, can i swap them out with the tubes from the K8.  THanks!

[trprbill]

I put the front end from a 1980 CB750F on a 1976 CB750F. Just had to slide the forks out and then into the '76's triple trees. Had to use the master cylinder from the '80 too. It was easy, and the forks are just over an inch longer.

[eurban]

f3 and k8 (all sohc 750s for that matter) have the same dimension fork tubes so you can slide the entire k8 assembly into your trees.  You will need to use the K8's fork because the k8 caliper mounts completely differently than f3 stuff and you will of course need to use the k8 wheel and rotor.  The master cylinder for the f3 will not be sized correctly for the single disc k brake setup so you should replace it with something that is properly sized for the application.

[zeus87]

got ya, im doing it the other way around.  Single disc to dual disk.  Im going to pull the front end off the non running F3 and put it on my daily driver K8.  Thanks!

[eurban]

Whoops, misread you there!  You will have to use the comstar wheel.  Don't know if the fork lowers from the F3 will fit on the K8 tubes but no matter what, you will have to use the F3 lowers.  I think I remember Terry from Australia talking about the compatibility of fork tubes.  Ask him. Use a master cylinder sized for dual discs. . .

[doobiebro]

I am currently working on the same conversion, although I am using the F2 forks for a K8.  It is a relatively easy job if you use the F3 (or F2) Comstar wheels.  If you decide to keep your K8 triple trees so the rake and trail are not altered, you will need to use a double banjo bolt on the brake switch splitter to run your lines to both calipers.  Or you could use the F3 triple trees which has the two line brake splitter, but you would also need the F3 master cylinder because the brake switch is integrated with the brake handle.  Either way, the fork tubes are the same size.  Also, if you want to run with a front fender you will need to use the F3 fender because the mounts are different.

[eurban]

Both the K8 and the F3 have the brake switch integrated with the master cylinder so the wiring will be correct.  Also to the best of my knowledge there is no difference in the location of the fork tubes relative to the steering stem in the F3 and K8 triple trees.  Honda moved the fork tubes closer (front to back) to the steering stem on all of the late bikes. The location and height of the handlebar mounts might be different though and as mentioned the F3 bottom tree has the provision for the brake line splitter.  As to the fork tubes, the question isn't whether or not they are the same size (they are) but rather if their is any difference in their machining that would make them incompatible with the fork lowers from the other bike. . . .
.