Author Topic: 78 CB750F "Modular-ish" cafe build? (Read 52588 times)

madScientist · « **on:** September 28, 2012, 08:36:08 am »

78 CB750F "Modular-ish" cafe build

First off I want to say the information and support on this site is incredible and thanks to everyone who's provided any kind of technical, creative, or other input. I've been lurking for about 4 months reading through virtually every post and have learned more in that time than i have in about 14 years monkeying around with 2wheelers.

This will be my first CB750 build. I've done several Kaw KZ's but going in a straight line is only fun for a little while and the KZ series seemed adverse to cornering.

Quick backstory on this bike. My dad and I bought this bike about 15 years ago when i was 14. It came as a $400 package deal with a 74 cb125s. I promptly got the 125 running and spent the better part of a year getting the 750 to run "right". It never did run perfectly but it ran and I rode the snot out of it. I then got a V-Twin intruder and lost interest in the old SS. Fast forward to me discovering this website and now I'm salivating at building up the 750 (now have funds and a VERY understanding girl to do so which helps).

The was thinking about making this bike a 'modular' cb. By modular I mean I want to be able to move from having a cafe bike with a cafe seat and relocated rearsets to a more "stock" style ride with the stock cowel (corbin seat) and standard sets within a couple hours of wrenching. It would live as the cafe primarily but when i go on a long ride or go 2-up i would switch up the configuration to accommodate for more comfort.

Please feel free to weigh in if anybody has tried this before, if this is a horrible idea, or any weirdness i might be overlooking. Right now my muse's are BOTH of Tweakin's bikes. I've been gushing at both of them for several months now...

Powerplant:
new primary chains
manually adjustable primary tensioner
hd cam chain
manual tensioner
836 dynoman kit
MRieck head magic (stage2...pending his availability of course)
different cam
stock carbs / airbox with different jetting

Things i'm not sure about:
backcut transmission -- would it be worth it for the setup above?
hd primary chains?
switch to a K head and then have the head work done or stick with the F head? I've read about the reliability issues with the F head and I would really like the bike to be solid

Frame stuff:
Gordon frame kit (procured...BIG thanks to Gordon!)
making the seat lock and hinge perch removable (going to bracket the lock and drill and tap the frame to accept bolts...the perch i'm going to weld nuts to the top of the frame and rill holes through the perch countersinking them)

Any tips or suggestions are very much welcomed and sorry for the long post.
-- i do have another F that i was going to make a dedicated cafe with a 915...but that's later...

madScientist · « **Reply #1 on:** September 28, 2012, 08:40:48 am »

Figured I'd post a couple pictures of the beast as well...

I did get the bike pretty well torn down through this week. Just need to pull the motor and I'll start fabbing. Hopefully more to come this next week.

srbakker · « **Reply #2 on:** September 28, 2012, 10:03:42 am »

Have fun!
And talk to me if you're looking for engine rebuild stuff - I have a bunch of things I'm offloading due to a change in plans, basically for what I paid for them.

brandEn · « **Reply #3 on:** September 28, 2012, 10:11:01 am »

Subscribed.
I will give you my 2 cents on the lower end upgrades. That stuff is always nice to have and if you can afford it then by all means spring for it! But, IMO the HD chains, backcut tranny, upgraded rods, and stuff like that is really overkill for these bikes. Yea that stuff is cool but man just those chains alone will break your pocket book. My advice is replace the primary chains with OEM, make sure your transmission dogs are in good shape, replace the bearings, primary tensioner, and button it up.

For the head. If you rebuild the the F head you will have no problems. The issues you hear about are due to the valve guide wear. Rebuild with new parts and your golden. If you put on a K head you will need K carbs. The F head spigots are different.

madScientist · « **Reply #4 on:** September 28, 2012, 10:54:55 am »

srbakker -- thank you and i'll let you know!

brandEn -- thank you for the advice and you're right about breaking the bank...the HD pri chains and tensioner kit alone is like 550! When i get in there i'll is there anything specific i need to look for on the dogs?

Thank you also for the head advice. I feel much better now as I really wanted to stay with the F head and carbs.

brandEn · « **Reply #5 on:** September 28, 2012, 11:24:48 am »

Glad to help. I learned alot rebuilding my F3 and am glad to pass along the info. For the dogs just look for obvious damage to the mating surfaces. Pits, nicks, dings, that sort of thing.

Retro Rocket · « **Reply #6 on:** September 28, 2012, 05:36:02 pm »

I'm on the other side of the fence, back cut box means smoother changes and less to no jumping out of gear, heavy duty chains cuts down on chain slap and the associated noise, and last a lot longer , rods are good insurance, i always over engineer my engines, actually most things i build, gives me piece of mind....

madScientist · « **Reply #7 on:** October 01, 2012, 06:58:37 am »

Thanks for the input fellas. I'm going to have to mull over this for a little bit. The heavy duty primary chains and a backcut transmission would eat up about 1/3 of the budget I have set aside for the engine.

I also haven't seen the inside of the engine yet but I'm kind of expecting to see damage that I haven't accounted for. I'm hoping to be into the engine by Monday so we'll see what time has done. Luckily I have a fair amount of vacation days left that I can use to feed my new obsession.

On a side note. I made the initial cuts for the frame kit last night. I still need to trim out the excised frame piece and weld it in. I'll have pictures of that to post up soon. I elected to made the horizontal cut on the triangle a little higher than center to allow for just a little more room to work. I dont have a compulsion to have things perfectly center and I'm the only one who'll see it anyway (except for the powdercoater and you guys since there will be pictures).

Mercutiojb · « **Reply #8 on:** October 01, 2012, 01:34:32 pm »

Subscribed. I have a 77F that I want to do in the same way. I love the cafe look, but the girlfriend will demand a ride from time to time!

I'll be curious to see how this turns out!

brandEn · « **Reply #9 on:** October 01, 2012, 05:42:07 pm »

Well think of it this way... I would be willing to bet that there are more 836 kitted hot rod motors WITHOUT all the expensive upgrades than with them. My 836 F3 engine pushes just over 70 HP with a stock (but rebuilt) lower end and I couldn't be happier.

madScientist · « **Reply #10 on:** October 04, 2012, 12:22:32 pm »

I've been getting about an hour a night this week to work on the tank. As of this morning it's completely torn down...sure i go to work at 6:30am but i'm all for waking up at 5 to get an extra hour in the garage :-D I woke up thinking about it anyway.

I have the frame kit welded in but I still need to finish the welds underneath the inserts and do some finish welding. I also need to do the bracket for seat lock as well as drill, tap, and thread the seat perch.

I have tomorrow and Monday off so I'm hoping to get this all done and get the first round of parts to the powder coater. I did notice that I have a LOT of play in the swingarm so I'm probably going to forgo sending that to the coater and send it to Hondaman instead for a little rebuild action.

Aiming to get the following coated in this first round:
--frame
--calipers
--kick stand
--fork legs
--trees
--battery box
--rear brake arm and bracket

It might be a bit lofty but we'll see...added pictures of the frame kit as it stands...

trippmann · « **Reply #11 on:** October 04, 2012, 12:37:36 pm »

ive been wondering for awhile now, what is the purpose of the frame kit?

builds looking good so far

madScientist · « **Reply #12 on:** October 04, 2012, 12:53:50 pm »

The kit allows for the removal of the bottom bars on the frame. therefore you can perform head work without removing the engine.

I also found out on Tuesday that it makes removing the engine SUPER easy. unbolted it from the frame, jacked it up about 3" with a floor jack, wiggled it over to my motorcycle lift. Done in 3 minutes.

750resurrection · « **Reply #13 on:** October 04, 2012, 01:06:19 pm »

Okay I'm all for the transformer aspect you want to do.

This other stuff is old hat and fine and all, but a good transformer rig (modular you called it) up would be groundbreaking.

Yes, so I'm thinking duplicate seat attachment scheme... you know you'll have to do your build with the transformation covered as you cafe convert it...

I like, don't let anyone tell you it's not possible. You can do it.

madScientist · « **Reply #14 on:** October 04, 2012, 01:27:15 pm »

I'm going to try to keep it as simple as I can. The seat conversion is the easy part.

The ingenuity is going to come in when it comes to moving the standard peg and foot control position to the rear sets since that involves a completely separate set of sets and controls. Complicating matters, from what i remember, the rear peg extension bracket on the F goes through the swingarm and i intend to run without a center stand. I'm thinking an additional bracket that will be held on by the swingarm bolt but will not be removed once installed. That way I can create rear sets that will attach to it as well as be able to fab up an extension for the rear pegs.

I'm also trying to avoid adding permanent tabs to the frame. Everything will be done in powdered black plate steel...might look at billet later.

750resurrection · « **Reply #15 on:** October 04, 2012, 01:46:00 pm »

Sounds good madScientist, allow the evil Einstein to flow through you...

I'm wondering about the taillight though on cafe vs corbin seat, isn't the taillight an issue too ?
noobaroo approaching 100 posts could be wrong here
I'll be over at the bar taking my beating
lol

madScientist · « **Reply #16 on:** October 04, 2012, 02:09:47 pm »

I'll examine a few other posts. I know tweakin did a build with a cafe seat and another with a corbin with the stock cowel. I didn't even consider the lighting issue. I really dont want to hang a light off the side either.

I could put a fiberglass cafe seat together. I have it down on the whiteboard in the garage...yeah i'm a nerd.

750resurrection · « **Reply #17 on:** October 04, 2012, 02:37:00 pm »

Hey I just remembered someone did it with the lighting in the rear bar around the back (bottom edge) so that would be a potential it will work.

madScientist · « **Reply #18 on:** October 05, 2012, 02:50:50 pm »

It's been a pretty productive day. I got the forks taken apart. Got the frame kit finish welded. Started taking the brake calipers apart but the pistons are really stuck in the housings and i'm trying to not grab hold of them with a set of channel locks.

I also spent about an hour with the acetelyn torch, a hammer, and chisel trying to get the lower bearing race off the tree post. The bearings literally disintigrated when I slid the tree off the neck...little marbles EVERYWHERE! The bottom race was fused to the lower part of the tree but a little bit of heat and brute force knocked it loose.

The icing on the cake though was getting the seat perch figured out. I originally planned to just drill holes and tap them. This proved futile when I realized the frame isnt' think enough to really accomodate threading...even with fine threaded bolts. So I flipped to plan B. That consisted of drilling bigger holes and welding nuts into the frame. SUCCESS!! I still need to grind it smooth but the nuts are in there and they work great! I also need to get the bolts to set flush against the frame. i might weld inserts underneath the perch between it and the frame and then drill the holes extra wide? Or perhaps grind the tops of the screws down since the phillips recesses are pretty deep.

Took a picture of my helper today...it never fails she'll look away as soon as you hit the camera button...

brandEn · « **Reply #19 on:** October 05, 2012, 05:56:31 pm »

For the stuck brake pistons. If you use a grease gun they will (should) pop right out. Just connect it to the bleeder and install a bolt in the banjo port.

750resurrection · « **Reply #20 on:** October 05, 2012, 06:36:25 pm »

Looks good madScientist.

madScientist · « **Reply #21 on:** October 07, 2012, 01:35:34 pm »

Today was a "poke-around" day. Meaning I just kind of poke around and stuff...make little bits of progress here and there.

Branden-- thanks for the advice on getting the pistons out of the calipers using a grease gun. However they were so stuck in there that method failed. I resorted to tightening the bleeder valves down and then blowing about 40lbs of air in the hose bolt hole and POP out they went! I'm still debating whether the pistons are salvageable. I think they can be polished up. I didn't notice any pitting...a slight bit of rust but nothing real severe. There was dried nasty in the caliper though.

I had no motivation to work on the frame today. I figure I'm off work tomorrow and can finish it up then. I just have to design and build a mounting bracket for the seat lock...no big deal right?

I did get into the motor today because I could not resist the urge to see what I'm working with. The head looks pretty dang clean. There wasn't any noticeable wear on the rocker arms but I still need to gauge them. The cam looked good too...shame I'm probably not going to use it. The jugs absolutely refused to come off. I had to delicately pry up on them to unseat and after that there was so much caked on gunk on the headbolts that i had to use a rubber mallet to get them clear. The surprising thing was how good the cam chain rollers and guides looked! You can tell they've been used but they haven't disintegrated. I got a few other pieces off too. Almost time to break open the case. Then I had to move on to setting the valve lash on the 66 mustang...

Sorry for the lack of photos. The camera was acting up. I'll have a slew to post tomorrow I'm sure.

A couple things I'm wrestling with:
-- What tabs, if any, should i whack?
-- Should I forgo sending the frame to the coater until I have the seat I want to use? Probably yes
-- Polish or coat brake caliper brackets? Leaning towards coating them silver

As I ponder those questions...back to reading through Tweakin's and Branden's builds...really dig what they did...

madScientist · « **Reply #22 on:** October 10, 2012, 10:45:29 am »

The frame mods that I planned are done. I finished up the removable seat perch as well as the removable seat lock. Once again I went with welding nuts in the frame. I also removed the helmet holder and a tab on the back leg.

I ordered the seat cowel yesterday from Airtech. They make them on order so it's going to be 3 weeks or so till i see that which isn't a big deal to me. I went with the 750F long chassis. I did not get the seat pan or tail light bracket. The tail light bracket might not be needed as I'm going to try and fashion the tail light system so that I wont need to remove it with the cowel when changing seats.

The 3 week wait time does somewhat impede progress as I'm not going to send stuff to powder coat until after I've confirmed that the seat fitment is okay and no other frame mod's are required. I think it will work out for the best though since I'm sending the swingarm to Hondaman for a rebuild. It was pretty sloppy. Please pardon the crappy pictures.

madScientist · « **Reply #23 on:** October 10, 2012, 10:47:31 am »

The top end of the engine is apart. I'm probably going to err on the side of caution but...is this cam chain guide and roller usable?

750resurrection · « **Reply #24 on:** October 10, 2012, 11:12:49 am »

Answer is, it is for me. If it's not cracked in half it's good to go.

dangit, okay sorry couldn't resist.

Nice work, and metal bench.

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Author Topic: 78 CB750F "Modular-ish" cafe build? (Read 52588 times)