I believe the K8 had the same engine as the F2 (different carbs)
Both had different carbs but the K8 engine will accept earlier carbs whereas the F2 engine will not. F2 has larger intake diameter on the head, K8 has the same size as earlier engines.
I have recently acquired a 1975 CB750F1 which I intend to fully restore over the next 12 months, however the engine casings are badly cracked due to the chain snapping, I have been told they are beyond repair.
I have been offered at a reasonable price a 20,000 mile engine from a CB750K8 ( these bikes were not officially imported to the UK)
Will the carbs from my F1 be suitable?
Will the standard F1 exhaust system or the equivalent Motad 4 into 1 aftermarket system fit OK?
Will the F1 wiring loom be compatible?
Are the frame engine mounting points the same?
Thanks.
I have only put a K8 engine in a '78 750F, not the '75 your inquiring about, but here's what I think:
1) carbs from your F1 will be suitable
2) Standard F1 exhaust should fit the K8 motor fine as I believe the external demensions are the same on the K8 motor as they are on your F1. K8 motor has studs sticking out of the head for mounting exhaust. If your F1 exhaust uses the bolt in "spigot" type mounts then these studs will need to be removed in order to mount your exhaust (The studs screw into the head and can be screwed back out).
3) F1 wiring loom should be compatible. The alternator,oil light switch,ignition, and neutral switch and any other electrical connections to the motor are the same on the K8 as on your F1. Pretty sure they are the same on all CB750's(70-78).
4) Yes, I believe that all the CB750 motors share the same mounting points. I could be wrong on this since I only have '78 frames so hopefully someone else will chime in on this.
The only difference between your motors that may be a problem is that the K8 runs a heavier chain, 630 rather than the 530 your running now. It may be as simple as taking the 530 front sprocket from your "cracked" motor and putting it on the K8 motor (I ran a 530 chain on the K8 engine with no problems). But it also may be that the front sprocket mounting point was moved out a hair on the K8 motor in order to fit the larger chain. If this were the case then your front and rear sprockets would be out of alignment.
I know this topic has been covered before so a search of the tech forum may yield this answer.
