Topic: Trying to make one bike out of two! K8 and F2 capability ?

[24on48off]

Bear with me as I try to paint a picture of my CB builds thus far. It started about two months ago when I picked up a 78 Cb750 k8 with title off craigslist for a flat $1,000. The bike was pieced together with at least three bikes but other than that it looked ok! The wiring was a mess, had a funny sound coming from cylinder #4, and It wouldn’t idle.. But still nothing that worried me too much for a bike kept in a barn for the last few years. 
Pictures of the K https://imgur.com/gallery/Mre19jE

Get the bike back to the shop and pull the spark plugs to check compression, cylinders 1-3 were around 90-110. Number 4 however was at 75-80 with a spotless sparkplug getting spark AND a very bent valve screw that had been banging against the valve adjustment cap.. That’s where I left it for the night.
Fast forward a few hours fearing the worst I start looking for a local donor motor on Craigslist to pull pieces from to replace whatever awaited me when I opened the motor the next day.  While searching I came across a 77 CB750 F2 SS that a guy just posted, a few hours away from me. Apparently, he had hopes for a Café build but once he tore the bike down lost interest and time now just wanted it out of his garage. SO the next day after some haggling no title and $200 later I had doubled my CB collection in about 48hrs and my girlfriend looked at me like I was crazy. What I was most excited about was getting a SS tank in such great shape since that’s the tank I planned on using for my build.

Pictures of the F https://imgur.com/a/johjJZN


SO now I’m not sure what to do..
Should I build the F2 and go through all the trouble of getting a title and converting the Comstar Mag wheels to wire spoke which is a no compromise for the look im going for.
OR
 Should I swap the F motor and tank into the K frame circumventing the Title and motor issue.. But are they compatible?

[Bankerdanny]

Nice pickup on the F, I just paid $140 for a tank by itself and felt quite good about the deal I got. The rear master is also pretty valuable.

All things considered the F is probably a better café candidate than the K. That year motor is the strongest of the 750's and it is geared a little shorter, so a properly running stock F will walk pretty much any STOCK K, although it also has a major weakness related to excess valve wear, so give the engine a good going over.

The F frame has some slightly different geometry and at least in the opinion of the reviewers back in the day handled better than the K. Then there is the twin disk front end, although at the cost of the Comstars that so many people hate (although not me). An F0/F1 rear wheel should bolt right up, I know an F2/3 rear caliper setup bolted on to my '76 F1 with no problem at all.

You can swap the K front end on to get a front wire and then do the twin disk conversion (K wheels are twin disk ready), although not with any of your F components except the master cylinder and the splitter. The stock F rotors (5 bolts vs 6) on your bike won't work with the K model wheel. I also don't know if the rotor spacing on single disk 750's is compatible with the F2/3 caliper spacing.

Personally I would part out the K, build the F and then get a title using the Vermont method (there are several threads here on how it works).

[24on48off]

You make it sound so easy haha. Thanks for the info, I spent the last few hours reading about the conversion options from the GL1000 front end swap to building your own wheel with aftermarket rings and getting it strung. Ive seen you comment in a few of the threads ive read and seem to be very knowledgeable so I appreciate the input! I think you're right, swapping the k frontend and buying a F0/F1 rear wheel would probably be the best course of action given I have most of the parts already. Could I use the controls from the K on the F?

[Bankerdanny]

Either controls will work, so use whichever you prefer.

I re-spoked the rear wheel on my 550 earlier this summer. It took me several tries as I had never done it before, but in the end I got it round and true and have about 250 miles on it with no issues. So don't be afraid to build your own.

I know several guys with GL front ends. The conversion isn't simple, but its not rocket science either. Converting your K front end to twin disks is the "simplest" way to get a twin disk wire wheel setup. There is a member based in Wisconsin, Godffrey, who has a resto business. He sells individual components or a complete kit to convert a single disk CB500/550/750 to twin disk.

How did you try to clean your rims? I am a big fan of 0000 steel wool and simichrome polish. It will clean up rims that you might not think were salvageable.

[scottly]

 Should I swap the F motor and tank into the K frame circumventing the Title and motor issue.. But are they compatible?

The F2 motor will bolt right into the K8 frame with no problems, and will be compatible with the K8 spoke wheel and sprocket.

[70CB750]

I blended K3 frame, tank and seat with 1978 F2 engine, wheels, brakes, swingarm and forks.  I had to fabricate one upper shock mount to accommodate the disc brake but the result is very satisfactory.  Love the power and brakes are excellent.

Oh, the brake pedal needed some alterations too, same for the rear master cylinder.  I used one from younger Honda. See my signature for the build thread.

[70CB750]

But it is only fair to mention, that the F2 engine has issues with valve guides at about 30 000 miles.   I learned that too late - aka after I picked up the engine - and it delayed me considerably since I had to install new guides, new valves and retainers and also cut valve seats.

[Jerry Rxman Griffin aka MuthaF'er]

If you go the F0/F1 rear wheel route be sure to use the K8/F2 rear sprocket carrier for the 10mm offset. 

[24on48off]

But it is only fair to mention, that the F2 engine has issues with valve guides at about 30 000 miles.   I learned that too late - aka after I picked up the engine - and it delayed me considerably since I had to install new guides, new valves and retainers and also cut valve seats.

The f2 has 26k miles on it, so it sounds like a valve overhaul is in order. where did you pick up most of your parts? Ebay?

[70CB750]

Cycle X for valves and retainers.  APE Bronze guides from some place else, not sure where from now.  Also tappet adjusters.