Topic: 72' CB750K2 Resto-Mod

[FridgeRaider]

Hey guys, I picked up a 72' & 78' CB750K, both in rough shape, about 6 months ago and have finally started getting serious about rebuilding the 72' how I want. The previous owner wouldn't split them up and I probably ended up paying to much for the condition that it is in. After restoring a 74' CB750 for my father, I knew I wanted to restore an early one in candy gold for myself. It has the original 4 into 4s and was supposedly a runner. I parted out a lot of the 78' to forum members to offset the initial cost. Hopeful those parts went to good use for their bikes.





I wasn't planning on writing a build thread since I'm not thinking of breaking the mold. So instead of cluttering up the general forum, I will ask my questions here and document my progress.  I want to keep close to the iconic original look of an early CB while modernizing the internals where I can. The plan for it is to be my daily rider so here are my goals for the build:

- Complete tear down of engine
- Upgrade to 836cc or Cycle X's 849
- Motogadget M-unit
- Hagon Shocks on rear
- Powdercoat everything (most of which I can do in house)
- Dual disc upgrade
- Replace old zinc hardware with stainless steel fastners
- Replace all wearable parts within reason

Here is my progress so far:







Engine removed with help from the pups.

I have set up a media blaster and powdercoating oven in my garage so I can blast and coat almost all the parts from the bike myself. The only thing I will have to outsource is the frame, swing arm, and chain guard. I went with satin black (70% gloss) and an All-in-One Chrome for my color choices. The chrome ends up being more of a shiny silver, which I wasn't immediately a fan of but once intermixed with the black and actual chrome/zinc plated/stainless steel bits, it looks really clean.



Fork leg lower after media blasting and then the others are after the chrome powdercoat:




Front Wheel:
- All-Balls bearings
- Laced and Trued w/ Zinc-plated spokes from 4into1.com
- Shinko 712s



Rear Wheel:
- All-Balls bearings
- Lace and Trued w/ Zinc-plated spokes from 4into1.com
- New EBC Drum brakes
- Shinko 712s





One of the previous owners was nice enough, among other things, to murder the original unicorn triple tree. He drilled two holes in it to mount the gauges with the later style plate. Thanks to Bill Benton for not breaking the bank with a replacement.





The plan is to work from the wheels inward, ending with a total tear-down of the engine. When removing the engine, I dropped the oil pan to find all sorts of metal shavings in the bottom and clogging the oil pump screen. The previous owner said his shop had got it running and I'm hoping if true, it was the shortest time possible. The oil pump screen was so clogged that it was holding back oil until some of the debris was wiped away. There was also a sizeable chunk of.....internal bearing maybe?





Let me know your thoughts on what it could be.

[Davez134]

I don't have a guess what that chunk is, but glad you're going through the motor. Great job on the powder! Following, as I have a soft spot for 72 restomods

[Stev-o]

Subscribed.  Looks like your off to a good start and your shop looks great.

[SOHC4 Cafe Racer Fan]

Please DO clutter this thread with updates. This will be a great project to watch.

[FridgeRaider]

Please DO clutter this thread with updates. This will be a great project to watch.

Haha, thanks.

I'm not working against any time frame here for the restore, just doing what I can between school and work. I like the challenge of working on motorcycles more than I do actual riding. That mindset probably puts me in a select group of weirdos. 

I do know that I want to upgrade the engine with a big bore kit since it's something that I haven't done before. I live in Central Florida (Polk County) and don't personally know of any local machine shops that are able to bore my cylinders to spec. I am open for recommendations from anyone who might know one that does competent work at a reasonable price. How I see it now is I will must likely have to ship my cylinders off. Here are the two options I'm thinking:

Option #1:
- Wait till Cruzinimage_co puts their cheap 836 kits (~$150) back online for sale
- Ship pistons and cylinders to a machine shop to bore
- Have machine shop ship freshly bored cylinders with corresponding pistons back

Option #2:
- Purchase Cycle X 849cc Big Bore Kit which has a higher 10 1/2 compression ratio (~$250) compared to Cruzinimage's 9.0 CR kit
- Ship cylinders to Cycle X
- Have Cycle X machine the cylinders to match their 849cc pistons I am purchasing from them and then ship both parts back

Cycle X offers a "budget" boring up to 849cc which includes: Surface top, bore and hone, for $150.00. That price doesn't seem outrageous to me coming from a reputable shop that specializes in our CB750s. Again, I don't have any experience in this and am going off of online reviews.

I'm looking for opinions on the pro's and con's of both options, or possibly a third option. I might purchase an after market cam and try my hand at porting the head to help round out the upgrade.
 

[SOHC4 Cafe Racer Fan]

I think the cruzinimage kits are great if you want to be budget conscious but you'll get much better performance from a higher-compression piston kit.

As for porting, I would not DIY. 

[calj737]

Harrison - I can handle the delivery of your head and jugs to a well-trusted shop here that I use, and then either ship them back or hand deliver on my regular spins through. Did the same thing for Wilbur and he got breakfast out of the deal too.  Let me know if that will help you-

[FridgeRaider]

Harrison - I can handle the delivery of your head and jugs to a well-trusted shop here that I use, and then either ship them back or hand deliver on my regular spins through. Did the same thing for Wilbur and he got breakfast out of the deal too.  Let me know if that will help you-

That would be awesome! I'll probably go with that option, thank you Cal.

With the cruzinimage pitsons, what else would you suggest replacing/upgrading? I know I want to go with Ape HD cylinder/main bearing stud kits and Kibblewhite valve springs.

Will the stock cam work well enough as is?

As for porting, I would not DIY. 

even if it was something simple as smoothing out the exhaust ports?

[bill440cars]

   Interested to see how this goes. Trying to get to where I can do a "Project" bike and checking out what ideas other folks have and how they go about it. This one is interesting, from the start. Lots of support on this forum and that is why it is going so well, along with the Great Folks here, from Staff to the members. 

[SOHC4 Cafe Racer Fan]

In my opinion, porting the intake is the more important and requires some experience to optimize performance.  You can also screw the pooch easily.  I'm not sure why you would only address the exhaust ports.

[PirateB]

The "chrome" powder coat looks great, I am really diging that

Sent from my SM-G900V using Tapatalk

[FridgeRaider]

The "chrome" powder coat looks great, I am really diging that

I'm excited to do the whole motor in chrome, It should turn out a little bit fancier than going with a standard silver. I love the look of polished aluminum but there is minimal maintenance with powdercoat.

   Interested to see how this goes. Trying to get to where I can do a "Project" bike and checking out what ideas other folks have and how they go about it. This one is interesting, from the start. Lots of support on this forum and that is why it is going so well, along with the Great Folks here, from Staff to the members. 

Thanks for the support, I will try to post updates when I can to keep it interesting.

In my opinion, porting the intake is the more important and requires some experience to optimize performance.  You can also screw the pooch easily.  I'm not sure why you would only address the exhaust ports.

I understand and agree that I can screw up a DIY port job fairly easy. I'm about 95% self taught from this forum, Hondaman's book, and a lot of youtube videos. My idea to try the exhaust side is to practice and gain the skills before trying anything on the intake side. I have/want to start somewhere 

Pics to follow once I have better internet.

[FridgeRaider]

I'm still collecting missing parts, powdercoating little peripheral bits, and finishing up the front wheel for dual disc conversion. I buggered the speedo drive while trying to modify it to fit and ended up purchasing a billet aluminum from forum member, Medyo Basto. Also, a big thank you to jamesw, FrankenFrankenstuff, harisuluv, and Lucien Harpress for help providing some needed parts.



Medyo Basto's speedo drive plate fits likes a glove


The speedo drive got the full treatment, I just forgot to take pictures. Disassembled, cleaned, powdercoated in chrome, re-greased, reassembled and installed on new drive plate.

   




Swing arm bushings removed




Steering stem races removed


The All Balls tapered bearing kit's top race is thicker than stock and will make it sit proud of the stem when installed. I can't remember if this is normal or am I forgetting something?


Little bits

[slikwilli420]

Powder looks killer on those little pieces. I have thought about getting set up for a while now. What is your setup?

[pipeguy]

Great job so far< gonna keep my eye on this one!

[FridgeRaider]

Great job so far< gonna keep my eye on this one!

Thanks! I appreciate the support.

Powder looks killer on those little pieces. I have thought about getting set up for a while now. What is your setup?

I took me awhile to piece it all together. I installed a dedicated 220 outlet in my garage to run either the compressor for blasting or oven respectively. I started off with the entry level powdercoating gun sold by harbor freight which had decent results but upgraded to the Redline EZ50. I consider it a mid-level gun with only a $350 price tag compared to competitors coming in at around $700. The only problem I've found with it is that it is very fragile so I handle it with care. The start up cost isn't terribly painful for home powdercoating and I enjoy being able to do most of the parts myself. I wonder what it would cost to have someone professionally coat all these little bits so I can judge if its worth it on a financial stand point. I'll probably need to do a couple more bikes to really get my money's worth.









10ft Grounding Rod and wire, used instead of the built in ground on the 110v plug




Custom made blasting cabinet. I use fine coal slag as blasting media, sold locally from any Tractor Supply Company.




Here's a before and after collage of the brake calipers. They came out absolutely perfect, the pictures don't do enough justice








I read over Hondaman's brake section in his book and decided to go with the semi-sintered pads as he suggests. 


Sleepy pup

[calj737]

I prefer using glass bead media on the aluminum. Less abrasive and cuts right through the oxidation and paint without peening the surface too much. Haven't tried the coal slag, but would be interested in how it compares for clean up and purging afterwards.

[FridgeRaider]

I prefer using glass bead media on the aluminum. Less abrasive and cuts right through the oxidation and paint without peening the surface too much. Haven't tried the coal slag, but would be interested in how it compares for clean up and purging afterwards.

I've always used coal slag since it's $8 for a 50lb bag and I can change it out regularly without breaking the bank. It comes in a variety of grits: Extra fine, fine, medium and so on. I've tried them all and prefer fine, medium grit and coarser is just too harsh. After blasting I simply blow out any particles with compressed air and spray it down with acetone before and after preheating it in the oven to prevent outgassing. 

Here's the latest results:

[calj737]

The finished product looks really beautiful Harrison 

[FridgeRaider]

The finished product looks really beautiful Harrison 

Thank you! 

I'm in the process of finishing up all the little parts: Calipers, foot pegs, hangar bolts, etc. Here is a finished caliper and bracket. It got a new seal and brake pads plus Dow corning high vacuum grease behind the pucks to hopefully decrease brake squeal.

[calj737]

And did you lubricate the pivot pin?

[FridgeRaider]

And did you lubricate the pivot pin?

  Sure did. I ran into a problem originally because I powder coated the pin. That ended up making it too thick to slide easily into the hangar. Coincidentally enough, Dino in one of his Hack-A-Week videos had the same problem which is why I held off on powder coating the second pin for the second brake caliper assembly. I resorted to stripping it back down, polishing best I could, and then going heavy on the grease. The hangar even got new o-rings thanks to jamesw, who I bought the second caliper parts from.

 

[jamesw]

And did you lubricate the pivot pin?

  Sure did. I ran into a problem originally because I powder coated the pin. That ended up making it too thick to slide easily into the hangar. Coincidentally enough, Dino in one of his Hack-A-Week videos had the same problem which is why I held off on powder coating the second pin for the second brake caliper assembly. I resorted to stripping it back down, polishing best I could, and then going heavy on the grease. The hangar even got new o-rings thanks to jamesw, who I bought the second caliper parts from.

Glad the o-rings are going to come in handy *thumb up*

That brake caliper looks absolutely brand new! 100X better than before. Fantastic job. Impressive.

[calj737]

I have taken to having mine shot with Dry Film Lubricant. Those and rocker shafts and some other internals seem to really like the bonded treatment.

[FridgeRaider]

I have taken to having mine shot with Dry Film Lubricant. Those and rocker shafts and some other internals seem to really like the bonded treatment.

What's the cost to have the rocker shafts done?


Latest update: I've finished just about all the little bits and have moved on to tearing down the carbs. The second caliper got the same treatment as the first and I replaced the rubber on all four foot pegs before reassembly. I was looking at the C-Style hangar and am still a little hazy on how to get it to work correctly since it doesn't actual mirror itself when switching fro the left fork to the right.



Carb rack teardown









This next pic came out blurry but I wanted to show what I had to do to completely disassemble the carbs. I strapped the stay plate down to a drill press and drilled out the stake that holds everything to the pivot shaft. The plan is to tap an M5 thread in it's place and us a bolt to hold the new stake in, once reassembled.











I'm excited for when I get to the motor. I had previously pulled the oil pan and filter cover when I separated the frame and engine. I added them to my assembly line of parts destined for media blasting/powder coating and they came out great. Hopefully this is a good precursor to the rest of the engine.