Topic: 77 "Black Motor"

[Heironymous Josh]

So, I've found a good deal on a 77, F2.  It is the "black motor" which I know has a little more power.  I have been using bikez.com to compare while shopping and the 77 has a considerably lower rating than the '74 K4 I already have a deposit on.  Is this site reliable or bs?  The ratings show a significant difference in the reliability of the black motor and the motor used in the K4.  Is this true?  I'm considering buying this 77 F2 and the 74 K4 to build up a bike.  I need some direction.  Which motor am I better off with?  I know the F2 has dual-disc front and single-disc rear whereas the k4 has drum rear and single disc front.  Which frame would I be better off with?  Will the 74 frame support the mounting of the F2's brake configuration.  I plan on going cafe style.  I know the tanks are different and placed differently.  And are bikez.com ratings worth a damn?  Thanks guys!

[Geeto67]

the bikez.com raiting are based on people's submissions which means that I wouldn't really pay any attention to it, or at least I would give this site more credence.

The advantages of the 77-78F wheels/brakes are that you can run tubless tires and the brakes are better. do a search on the 77-78 F head on this site and you'll see why they have less longevity - it is just bad valve design that will lead to oil consumption - not anything that will result in immediate catastrophic failure

the 77-78 F bike uses a larger countershaft and you will need the cush drive off the 77-78 K bike to use the 74 stock drum, or alternativly you can just use the whole 77-78 SS rear end and weld mounts for the rear master cylinder.

The tanks all mount the same, the seats are different and will have to be paired to the frame (if you use the 77-78 F frame, use the 77-78 F seat and tank, same with the 74 K). If you are going to run a custom cafe seat pan then run any tank you like. 

[Hockers Choppers]

I have a 78 cb750f supersport F3. I'm rebuilding the engine with a k topend. the f head is junk, but the k head and cylinder bolt right up. If you are going to build a hotrod this is the way to go. The f bottom end is better and the brakes are also better. Let me know if you have any questions. I've found out a lot of things the HARD WAY!! Jesse

[Hockers Choppers]

OH, I see your in Denver? Forget what I said about the f bikes, They are crap!!! sell it fast!! I'm in western Kansas and can come take that pile of junk off your hands for gas money!! Yeah, like I need another project!
Jesse Hockersmith
Victoria, Kansas

[Jerry Rxman Griffin aka MuthaF'er]

Josh,

Don't believe a word he says. He's not allowed across the state line. You have various other friends here in Colorado.
 

[Terry in Australia]

Geez, and I thought I was a mercenary bastard, only 3 replies and two of them are trying to part you from your bike, ha ha!

Anyway, the F2 is a great bike, but "can" be fragile, it's not a given that the one you're interested in will have any problems, particularly if it's a well loved, and well maintained, example. My previous F2 was such a bike, and was as reliable as any K bike I've ever owned.

The benefits of the F2(and F3 as they're the same bike)is that it is the best handling, best braked, and fastest of all the 750 family, as it wes specifically designed to combat bikes like Suzuki's GS750 and Kawasaki's KZ650, as both bikes were killing Honda's sales of CB750's.

Coversely The F/F1 and K7/K8 have probably the best engine as far as reliablity goes, but they're ugly, and it can be claimed that they were responsible for the untimely demise of the SOHC 750 and the rushed release of the early DOHC750's which were just as ugly, and unreliable to boot. (a good thing to do to them)

I've got a restored F2 and an unrestored "bitsa" K2, so I've decided to build a better K, utilising the beauty of the K0-K6, with the power and the handling prowess of the F2.

Basically I'll fab mounts for the rear MC on the K2 frame, then swap out the entire F2 front and rear end, the F2 engine, (but with a worked over 836CC K2 top end and Keihin CR29mm carbs)topped off of course with the K2 tank, seat, sidecovers etc. This I believe is the ultimate CB750 and will be great fun as a coversation piece at my "Old Farts" Ulysses Club meetings fooling guys who thought they new their 750's with my "factory look" CB750K9, ha ha! Cheers, Terry.

[Geeto67]

hey terry, as long as you are converting that k2 to comstars, why not find a DOHC wider rear rim (reverse comstar) and run a 150 series rear tire? I think it was the 82 900fs that had that wider rim (if you really want to be a badass find the cb1100f gold trispokes).

[Jerry Rxman Griffin aka MuthaF'er]

"Coversely The F/F1 and K7/K8 have probably the best engine as far as reliablity goes, but they're ugly, and it can be claimed that they were responsible for the untimely demise of the SOHC 750 and the rushed release of the early DOHC750's which were just as ugly, and unreliable to boot. (a good thing to do to them)"
 
Hey you mercenary bastard (thank you, always nice to be put in such good company!), what do you mean ugly, that's my bike you're looking at, not my old lady!  I'm here to help and I'm just down the street.

[Terry in Australia]

"Coversely The F/F1 and K7/K8 have probably the best engine as far as reliablity goes, but they're ugly, and it can be claimed that they were responsible for the untimely demise of the SOHC 750 and the rushed release of the early DOHC750's which were just as ugly, and unreliable to boot. (a good thing to do to them)"
 
Hey you mercenary bastard (thank you, always nice to be put in such good company!), what do you mean ugly, that's my bike you're looking at, not my old lady!  I'm here to help and I'm just down the street.

OOPS! Did I say "ugly"? What I really meant was, er, "conservative"! Yes, that's right, "conservative" is what I meant, you know, like chicks who work at Library's and secondhand book shops, whereas F2's and K0-K6 are like lingeree models.

Nothing wrong with those F/F1 and K7/K8 "chicks" Griffy, they might look, er, "conservative", but they've got hearts of gold! You're familiar with the expression, "she's got a great personailty"? Well, that's what I'm talking about, ha ha!

[Terry in Australia]

hey terry, as long as you are converting that k2 to comstars, why not find a DOHC wider rear rim (reverse comstar) and run a 150 series rear tire? I think it was the 82 900fs that had that wider rim (if you really want to be a badass find the cb1100f gold trispokes).

G'Day Mate, that's not a bad idea, I've got an 1100F back wheel in my garage, but I really want it to look like it might have been a factory prototype, so I want to use items that were available in 1977?

I may try to use a pair of the "all alloy" Comstars of the period, (used on CBX's, I believe) they really are superlight, I've got a front one, I just need to find a rear, and make it fit. I've got a 150 rear tire on my K1, but had to remove a fair amount of metal from the centre stand to fit the bugger, and I've had to fab my own chain guard, there's no room for the OEM item now, ha ha! Cheers, Terry.

[Geeto67]

G'Day Mate, that's not a bad idea, I've got an 1100F back wheel in my garage, but I really want it to look like it might have been a factory prototype, so I want to use items that were available in 1977?

weren't the cb1100f tristar gold rims (identical to the cx500 turbo rims btw) just a copy of the first performance machine rims from the 70's?

I'm pretty sure you can use a 1979 cb750F back end (I think on some of the early 79 F's the swingarm even fits the SOHC frame) if you want to go crazy with it. The swingarm is longer but then you can run the DOHC cb750F Showa shocks (or those 900F piggyback showas) for that killer factory setup (the DOHC shocks are an 1" longer than SOHC shocks). Then it is all period correct for 1979.

[Jerry Rxman Griffin aka MuthaF'er]

"Nothing wrong with those F/F1 and K7/K8 "chicks" Griffy, they might look, er, "conservative", but they've got hearts of gold! You're familiar with the expression, "she's got a great personailty"? Well, that's what I'm talking about, ha ha!"

Yeah, that's like "roll her in flour to find the wet spot" 

[DammitDan]

Heironymous Josch,

I gotta know, did you get the first part of your name from Elder Scrolls 4? 

[Heironymous Josh]

OH, I see your in Denver? Forget what I said about the f bikes, They are crap!!! sell it fast!! I'm in western Kansas and can come take that pile of junk off your hands for gas money!! Yeah, like I need another project!
Jesse Hockersmith
Victoria, Kansas

Funny, funny!  Thanks for the input.  I may be asking you questions as my project is starting to take focus. Building the motor with the K topend solves the problem with the F valves I was told about.  Thanks, my friend!

[Heironymous Josh]

Josh,

Don't believe a word he says. He's not allowed across the state line. You have various other friends here in Colorado.
 

RxmanGriff, good to know.  You can't always spot this riff raff at a glance.  I'm glad to meet other Colorado SOHC owners!  We'll have to do some riding this summer!

Josch

[Heironymous Josh]

Geez, and I thought I was a mercenary bastard, only 3 replies and two of them are trying to part you from your bike, ha ha!

Anyway, the F2 is a great bike, but "can" be fragile, it's not a given that the one you're interested in will have any problems, particularly if it's a well loved, and well maintained, example. My previous F2 was such a bike, and was as reliable as any K bike I've ever owned.

The benefits of the F2(and F3 as they're the same bike)is that it is the best handling, best braked, and fastest of all the 750 family, as it wes specifically designed to combat bikes like Suzuki's GS750 and Kawasaki's KZ650, as both bikes were killing Honda's sales of CB750's.

Coversely The F/F1 and K7/K8 have probably the best engine as far as reliablity goes, but they're ugly, and it can be claimed that they were responsible for the untimely demise of the SOHC 750 and the rushed release of the early DOHC750's which were just as ugly, and unreliable to boot. (a good thing to do to them)

I've got a restored F2 and an unrestored "bitsa" K2, so I've decided to build a better K, utilising the beauty of the K0-K6, with the power and the handling prowess of the F2.

Basically I'll fab mounts for the rear MC on the K2 frame, then swap out the entire F2 front and rear end, the F2 engine, (but with a worked over 836CC K2 top end and Keihin CR29mm carbs)topped off of course with the K2 tank, seat, sidecovers etc. This I believe is the ultimate CB750 and will be great fun as a coversation piece at my "Old Farts" Ulysses Club meetings fooling guys who thought they new their 750's with my "factory look" CB750K9, ha ha! Cheers, Terry.

Sorry for the slow reply everyone!  I didn't mean to ignore you.  I followed the thread for a day or two with no replies and just noticed all of the comments.

Terry, thanks for the advice.  It sounds like I've got some go-to resources as my build continues.  The bike seems to be very well taken care of, but I haven't peaked inside where it really matters yet.  I may drop the sump this weekend.  I'll keep you guys posted on the build.

Josch

[Heironymous Josh]

Heironymous Josch,

I gotta know, did you get the first part of your name from Elder Scrolls 4? 

Actually, Heironymous Bosch was a Dutch painter in the 15th and 16th century but I have been asked about the elder scrolls a few times now.  I don't even know what they are but I'm curious as hell.