Topic: CB750 K5 (1975) - Cafe Build

[AtTheRaces]

I am a long time follower on the forum and thought it would be best to start documenting my progress.

A little about the bike...
1975 CB750 K5 (to repeat the title)
Purchased in April 2012. It was mostly stock at the time minus the aftermarket 4 into 4, handle bars, seat cover and side covers. It was my first bike purchase. Little did I know the rabbit hole I got my self into. It only takes a little defect for the wound to start spreading. Come to find out the bottom half of case had a hole near the front sprocket. The PO tried to use JB weld to seal it up the best he could but it had oil spraying everywhere. So one thing lead to another and here we are five years later with countless man hours already poured into the build not to mention I've moved twice, switched jobs, gotten married and worked on numerous other side projects to get where I am at.
My goal was to have the bike up and running by Memorial Day weekend but I've run into some set backs with parts on order so that will have to be pushed.

Ill post a before photo below along with some project photos. I'll also list out my build ticket but to get a sense of what I've been doing here is a high level overview:
- 836cc big bore kit
- webcam camshaft
- HD case studs
- HD cylinder studs
- HD cam chain
- HD primary chains
- Glyptal line cases
- progressive front springs
- Hagon rear shocks
- all new bearings in the wheels and steering head
- numerous custom brackets and a cleaned up "tabless" frame
- electrical: m unit, Oregon reg/ref, dyno coils, shorai lithium battery, pamco ignition



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[AtTheRaces]

This the original bike i purchased in 2012


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[AtTheRaces]

This what the bike looks like now



I got a SS tank and a custom oil tank usually use on bobbers and mounted it under the seat.



I welded up a custom seat pan/rear cowl. It houses the rear tail light. I might put some other electronics in there too.

 

Here is a good side view. This is before the seat pan was all welded up. You can see the custom battery box as well.


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[SOHC4 Cafe Racer Fan]

What did you do to address the crankcase hole?  Did you have it repaired or replace the cases? 

Are the three taillights just cut-outs in the seat to single taillight unit underneath or are they 3 separate units.  If the former, I would consider aperture openings.  You want your brake lights to be well-seen especially in daylight by driver coming up on you with mediocre brakes.

[AtTheRaces]

Double check your tire clearance to the seat pan under full compression. Many who install a new hoop encounter just such a problem.

Its nice body work on that cowl, by the way  Love the beaded and recessed round lights. Nice touches!

Noted on the clearance issue. During the fabrication of the battery box I was crawling on and off the seat, compressing the shocks and not notice any issue at the time. 🤞


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[AtTheRaces]

What did you do to address the crankcase hole?  Did you have it repaired or replace the cases? 

Are the three taillights just cut-outs in the seat to single taillight unit underneath or are they 3 separate units.  If the former, I would consider aperture openings.  You want your brake lights to be well-seen especially in daylight by driver coming up on you with mediocre brakes.

For the crankcase I bought a used CB750 F1 case off eBay. The original case was too chewed up for my liking.

As for the rear tail light, it is a single LED light mounted to and under the cowl via some welded brackets. I also have a mud guard/shield which will protect the light from any road debris. With the shield and the cowl it's likes own little compartment which I was planning in painting the inside a high gloss black to act a mirror to help reflect the light.



Top view of the mud shield. The shield is mounted to the rear frame cross member which I welded on as well.



Bottom view of the mud shield. I didn't want any fasteners showing in this section so this has a bracket which mount to the rear frame cross member as well.


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[SOHC4 Cafe Racer Fan]

Since it's a single LED unit lighting the 3 holes, you might want to consider making the holes larger in diameter or shape.  I am sure they will be seen well at night, but in bright daylight, you want that semi-truck, texting soccermom in a SUV noticing that you have applied the brakes.  Even with these older bikes, they stop faster the many cars.  Bikes vs. rearend collisions with cars/trucks are not pretty. End of safety rant.

[bwaller]

I had an experience (in my car)where I damn near rear-ended a buddy on his GSXR1000 with a bloody tiny little light that just wasn't well illuminated. It scared the #$%* out of me because I'm a biker. I let him know as soon as we got to our destination.

Be responsible for your own safety, just because it might look cool doesn't make it right.

[AtTheRaces]

I finished the last of my fabrication this week.



Mounted the motoscope tiny in the headlight bucket.



Made a shock mounted license plate bracket. 



Had to use a little heat to release the caliper piston.



Dropped off the parts at the powder coaters. I'm getting the 4 into 1 exhaust ceramic coated. There is a 2-3 week lead time.

In the meantime I'll be prepping for what I think is the largest challenge: wiring. The next post will be my wiring diagram.


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[AtTheRaces]

Below is my wiring diagram

  COMPONENTS● Motogadget M Unit v.2● Motogadget M Controls● Emgo ignition switch● Oregon REG/REC● Shorai Lithium Ion Battery● Dyna, 3 ohm coils● Hondaman resistor pack● Pamco Ignition● Motogadget Motoscope Tiny Gauge● Motogadget M Blaze turn indicators● LED Tail Light





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[SOHC4 Cafe Racer Fan]

Below is my wiring diagram

  COMPONENTS● Motogadget M Unit v.2● Motogadget M Controls● Emgo ignition switch● Oregon REG/REC● Shorai Lithium Ion Battery● Dyna, 3 ohm coils● Hondaman resistor pack● Pamco Ignition● Motogadget Motoscope Tiny Gauge● Motogadget M Blaze turn indicators● LED Tail Light





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I might be a bit biased, but with all of these nice components, you might want to ditch the Emgo ignition switch.  They are not very well made.  There are better aftermarket options, including the M-Lock, a better key unit (https://www.lossaengineering.com/products/lossa-custom-ignition), a modern key switch or a clean/refurbished stock ignition unit. 

[AtTheRaces]

Below is my wiring diagram

  COMPONENTS● Motogadget M Unit v.2● Motogadget M Controls● Emgo ignition switch● Oregon REG/REC● Shorai Lithium Ion Battery● Dyna, 3 ohm coils● Hondaman resistor pack● Pamco Ignition● Motogadget Motoscope Tiny Gauge● Motogadget M Blaze turn indicators● LED Tail Light





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I might be a bit biased, but with all of these nice components, you might want to ditch the Emgo ignition switch.  They are not very well made.  There are better aftermarket options, including the M-Lock, a better key unit (https://www.lossaengineering.com/products/lossa-custom-ignition), a modern key switch or a clean/refurbished stock ignition unit.

I double checked my key switch. Thought it was Emgo but its actually a universal key switch made by V Twin. We'll see how it works 🤷‍♂️


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[AtTheRaces]

Finally getting back into the build. Over the last couple of weeks I've finished up my parts ordering and my frame and parts have been powder coated.



Powder coated parts pick up. I had the frame done in matte black.



Unwrapping very carefully



Powder coating quality is very nice. Brake caliper done in satin black. That's my buddy's AMC Eagle in the background



He had a little trouble with the timing the other day.



Engine installed,new steering bearings and swing arm bearings. Waiting on wheel retainers to get delivered before I do the wheel bearings.



Next steps: work on rear set linkages, mount the remaining controls, finish plumbing the oil system, and wiring.



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[AtTheRaces]

Churning along slowly with the build. I've run into some minor set-backs. Wrong rear bearings, wrong front brake pads, etc. but it keeps going.

I've got a set of brand new EBC FA13 front brake pads never used if anyone needs them. I'll let them go for cheep to forum members. DM me.

I got the controls and headlight mounted.



Mounted the battery, m unit, solenoid and ran the larger cables. I've got very little clearance from the bottom of the seat pan to the 10AWG Wire going to the solenoid. I have some right angle connectors in the mail so hopefully that will solve that issue.



I mounted the coils in their original spot and barely had enough clearance on the bracket for the Oregon reg/rec to clear the push pull mechanism on the carbs. As you can see it was a tight fit.



I polished up the aluminum bowls and ring clamp on the carbs. Re-jetted to 135 on 2 & 3 then 132 on 1 & 4. Installed the velocity stacks and carbs.

Can't wait for this baby to howl.




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[theDQG]

I finished the last of my fabrication this week.



Mounted the motoscope tiny in the headlight bucket.

Can you tell me more about how you did this? I'd appreciate more info. I want to do this on another build I have in the works.

[AtTheRaces]

@DQG

For the gauge in the headlight I first measured the OD of
my gauge, halved  that measurement to get the radius and used a draftsman compass to place a scribed circle in the position I wanted on the headlight bucket. Once I removed the bulb i drilled a pilot hole at the center of the scribed circle. I then cut the hole using a hole saw bit with a diameter slightly smaller than that of the circle. Finished rounding and smoothing the hole with a dremel sander and a fine file.

Hope this helps!


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[theDQG]

@DQG

For the gauge in the headlight I first measured the OD of
my gauge, halved  that measurement to get the radius and used a draftsman compass to place a scribed circle in the position I wanted on the headlight bucket. Once I removed the bulb i drilled a pilot hole at the center of the scribed circle. I then cut the hole using a hole saw bit with a diameter slightly smaller than that of the circle. Finished rounding and smoothing the hole with a dremel sander and a fine file.

Hope this helps!


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Thanks for the SBS. How did you secure it? Did you use a grommet?

[AtTheRaces]

@DQG

Inside the HL bucket I welded two Steel L brackets. Each bracket has a hole to accommodate an M3 bolt. The gauge has two M3 mounting bungs which hold it in place. After welding I had the bucket powder coated.


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[theDQG]

@DQG

Inside the HL bucket I welded two Steel L brackets. Each bracket has a hole to accommodate an M3 bolt. The gauge has two M3 mounting bungs which hold it in place. After welding I had the bucket powder coated.

Actually, there is an even easier means:
MotoGadget makes and sells a "cup" for the gauge to sit within below whatever bracket (in this case the headlight shell). Follow ATR's method for cutting the hole, drop the gauge thru, slip the cup up, onto the gauge from underneath, use M3 bolts to secure cup to gauge. The cup then "pinches" the gauge down onto the headlight bucket, everything solid and secure. No welding, no extra space consumed within headlight.

Yeah, you gotta buy the cup, buts its pretty cheap-

Thanks for the good tip.

This the cup you talking about?

https://revivalcycles.com/products/outer-cup-a-motoscope-tiny-by-motogadget

[theDQG]

Thanks.

Sorry for the thread hijack, ATR.

[AtTheRaces]

Started wrapping thing up on the build. Wiring the ignition system, running all wires, installing new brakes, installing new wheel bearings, kick stand installed, exhaust system installed. I also got got the engine started.

Installed these EBC sintered brake pad in the front. It's parked with the the EBC 1062LS front rotor. The rivets on the rotor interfered with the brake caliper and pad while spinning the wheel so i had to grind the pad down a little and sand the outside caliper body to gain clearance.



✔️Seat, tank, ceramic headers, cone muffler
I move the muffler forward about 5 inches after taking this photo. I was going to make a n aluminum bracket for the exhaust. It's just held on by two self tapping screws for now.





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[SOHC4 Cafe Racer Fan]

Love F tanks on K builds. The tank has a great shape.

[AtTheRaces]

I took the bike out for its maiden voyage this past weekend. It's always a bit nerve wracking when you're asking yourself "did i torque those bolt to in-lbs or ft-lbs?" Or  "I think it looks right".

At any rate the bike has no issues starting up, no oil leaks, no fuel leaks, no back firing, shifts okay through the gears. It gets hung up a little going from 1st to 2nd. Not sure how I get it to engage every time without having to really lift up hard on the lever.

The engine is strong. I can really notice a difference with there 836cc big bore kit coupled with the web cam. Albeit, on city street only. Once I put some more miles on I'll hit the freeway to really test it out. I want to break it in around town first.

Does anyone have recommendations for breaking in an engine rebuild?

One other issue I have to sort out is the braking sensitivity. I wish it would stop faster. Even with new pads in the rear and new EBC pads and rotor up front it seems a little slow to stop.

After the holiday I'll begin on the seat and paint.

 




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[SOHC4 Cafe Racer Fan]

Do not run it at a constant rev for sustained periods of time.  Vary the revs, ride it under load and do not baby it, but do not redline it either.  Make sure it has time to go through several heat cycles.  Ride, cool down, ride, cool down, etc.  Change the oil after 500 miles.