Topic: Finished - 1977 CB750K7 full restoration from rustbucket to almost new

[Speedswitch]

Hello everyone,

As i am new to this forum i want to start by introducing myself: I am a 30 year old living in Holland and i've spent the last 8 months restoring a 1977 CB750 K7 back to factory original condition.
This is my first motorcycle and my first restoration, though i do have some experience working on cars. Before you start reading, i want to say how awesome it is to have the sohc4.net forum as a resource when working on a bike like this, it has helped me immensly to be able to access this immense amount of knowledge when i couldnt work something out.

I also want to say that this topic does not fully cover all aspects of the restoration or describe everything that i have done, so you will see that a few things may not be covered (such as rebuilding the brake calliper, the head light, rear wheel etc). This is simply due to the fact that i never intended to fully document the restoration. I just took some pictures here and there, but also frequently forgot to take pictures. And i only decided to create this topic afterwards when i saw how much material i had. Anyway, here we go and i hope you enjoy 

Preview

As the restoration is already pretty much finished i can show some befores and afters

Before:


After:


Build log

I bought the bike in july 2018 from an online ad. I had zero knowledge of motorcycles at that moment, not to mention any knowledge of CB750's. Therefore i had no idea if the bike was anywhere near complete (hint: It wasnt) and how much time, effort and money it would cost to get it in decent shape. In hindsight i should have chosen a more complete bike to do a full restoration on.

Part 1 - The before's:



As you can see the bike was in less-then-perfect condition when i bought it. Hell, it was pretty much held together by rust and external air pressure.
Shoutout to the brave and beautiful wifey who drove this roling junkyard home.



Part 2 - The teardown:

After safely parking the bike in the garage that would be its home for the next 8 months, i started tearing down the frame to reveal all the nasties. I have to say that this was the first moment i realised what i had gotten my hands on. This was going to be a big project.



Some may have already noticed the big CMS box in picture 4, i guess you can already guess what was inside 
I realised i have no picture of the engine removal. The reason for this is that it took me and a friend about 4 hours to remove it from the frame, because the front left engine mounting bolt was completely corrosion-welded to the block and we had to drill it out entirely. So i had a little too much on my hands to take pictures.

Part 3 - Engine disassembly:

After removing the engine from the frame, i made a small engine stand from a couple of 2-by-4's i had left lying around and started disassembling the engine.


The engine stand allowed me to also tilt the engine forward so i can access the oil pump:


Plenty of nastiness going on here:


Cam looks somewhat worn but turned out to be usable after measuring wear:


Looks like it may have burned some oil:


After splitting the cases i realised i was not the first one to get into this engine: The cases were split before and whoever re-assembled it had been a little bit trigger-happy with the liquid gasket. This #$%* was everywhere. Also, there was a considerable amount of metal shavings and a very large metal chunk. I have never been able to find out where it came from, even though i have inspected each and every engine part multiple times closely

[SOHC4 Cafe Racer Fan]

I look forward to seeing more of your build.  I hope you carefully inspected the transmission for wear in light of your report that there were metal shavings in the oil.

[Speedswitch]

I look forward to seeing more of your build.  I hope you carefully inspected the transmission for wear in light of your report that there were metal shavings in the oil.

Thanks, the only wear i have found in the transmission was some negligable wear on some of the gear dogs and significant wear on the center shift fork (which i have replaced). Other than that everything looked mint.

Part 4 - Engine reassembly:

So, picking up where we left off, after disassembling the engine i carefully inspected and measured the individual parts and ordered replacement parts where needed. Basically this came down to replacing all bearing shells, piston rings, transmission bearings, the central shifter fork, all gaskets and o-rings, the primary and cam chains, the exhaust valve guides and rebuilding the oil pump. Even though i had feared the worst based on what i saw when i split the cases, the crankshaft was absolutely mint and the pistons and cylinders were well within their wear limits. Not too bad for an engine with 54.000 miles on it.

I dropped off the engine parts at the hydroblaster and picked them up again 3 weeks later:



Losely stacked the cylinder, head and cam cover on top to get a good look at how it would turn out:


Time to assemble! Surgery room prepared:


Installed new main bearings, transmission bearings, primary chains and rotating assembly:


And cases joined:


I used hondabond 4 to join the cases. Damn, this stuff goes off fast. Its a race against the clock to get it all applied.

Installing the cylinders (after giving them a light hone):


And the head:


I used a very thin coat of Permatex gasket sealant around the edges of the base gasket and the cam chain tunnel of the head gasket.

I forgot to take pictures of the installation of the cam etc, but here is the end result ready for installation in the frame:



Speaking of the frame...

Part 5 - Powder coating and plating:

While the engine parts were off to the hydroblaster, i stripped the frame and sent it off to the powder-coater. I also got all hardware replated and some items rechromed, such as the rear wheel and rear fender.

The frame parts returned from the powder-coater:




Initially i was quite happy with the powder coating, but upon assembly i ran into a lot of clearance issues. For example, the PC layer was so thick i could not get the rear axle to fit into the swing arm, and the PC company did a bad job at masking off other relevant parts (they even didnt mask the steering lock).

Fortunately around this time the parts returned from the electroplater made me a lot happier:





And finally, the chrome shop returned these beauties (though they did charge me €500 for it) 

[Speedswitch]

Part 6 - Electrics, wheel and seat:

When i bought the bike the electrics were working, but the wiring loom looked horrible and there was severe corrosion and dirt on nearly all contacts and connectors. As you can see the connector to the rectifier got a little bit hot:


(I replaced it obviously)

The condition of the wiring loom was actually so bad that i went straight for the last-resort option: I soaked the entire loom in a bucket with hot water and industrial degreaser. The wires and connectors came out surprisingly good:


I then dried everything carefully, re taped the loom and reinstalled all electric components after cleaning them up. The rectifier was no longer usable so i replaced it with an OEM Honda solid-state rectifier:


The handle bar controls were also not in good shape. Took them apart for painting and cleaned the insides while i was there:


After applying egg-gloss two-pack paint and carefully filling the letters with red paint:


Before i could begin reassembly a few more things needed to happen. I had the front wheel rim replaced and relaced by a nearby honda specialist. The rear wheel rim however is no longer available, so after rechroming i decided to relace it myself. Closeup shot of the result:


Also, i had bought a new (used) seat, because the one that came with the bike was non-original and completely rusted through. Unfortunately the new seat also had some minor surface rust. Sanded the seat base and applied a rust-inhibitor and two-pack paint. I think i will remove the padding and have the seat base powdercoated in the next winter break:



In the back ground you can see the air filter housing which was also painted at the same time, just like the inner fender and several other parts.

[Speedswitch]

Part 7 - Front forks and frame reassembly:

The front forks were in quite bad shape, the outer fork tubes were badly corroded and the inner tubes badly worn and rusted. When draining the fork oil, only the tiniest bit of oil came out, maybe about a table spoon in quantity. It was also pitch black and smelled horrible. The inner fork tubes were no longer usable as they had corrosion around the area where they ride agains the fork seal. I was lucky to find brand new (NOS) Honda fork tubes on an online ad for only €200. With these, some new seals and a lot of polishing, it was time to reassemble:

One polished, one.. crappy?



Having polished both of them:



Slowly starting to put the frame back together, new rear shocks, needle roller bearings for the swingarm, tapered roller bearing for the steering assembly and a new handle bar:


I painted the inner fender (And all other plastic parts) in this egg-gloss two-pack paint, i think it looks nice on plastic. Love the texture. New warning decals were applied too:




This is where i forgot to take pictures for quite a bit, but in the next picture i installed both front forks, the front wheel (which meanwhile was fitted with a new tire) and the front fender:

[Speedswitch]

Part 8 - Reassembly (continued) and engine installation:

As the front wheel was now in place, the frame stood a little more stable on its center stand and installing the engine was now possible.

Frame ready for installation:


I put the engine stand on a pallet to get to the proper height relative to the frame. I then used a wooden beam, some rope and 2 stacked beer crates to create a way to lift the engine without too much effort and carefully slide it into the frame. With the help of my father in law and his brother we were able to install the engine in less then 5 minutes this way.


With the engine installed, now came the time to install the rear wheel and chain:


I like this view, such a shame that a tank will block it soon:


As always, the details matter. New warning decals from Yamiya installed on swing arm and chain guard:


With the seat installed it is now really starting to resemble a bike again:


Not shown in the pictures are some other things i worked on in the meantime: The coil pack that came with the bike was not original and i had doubts about its quality, so i replaced it with a brand new OEM Honda pack. As the front brake was not really doing anything when engaged, i disassembled the master-cylinder and rebuilt it with a rebuild kit. Unfortunately this did not result in a proper working front brake, the master cylinder leaked even after rebuilding it, and the brake pressure was still quite bad. Therefore i have replaced the master cylinder with an after-market one, which did absolute wonders for brake performance and, bonus, does not leak brake fluid all over the place 

[Speedswitch]

Part 9 - Exhaust and tank:

As you may have noticed in one of the first pictures in this topic, you'll see a big CMSNL box. Guess what's inside..   

I wanted to mount a 4-into-4 exhaust system right from the start when i bought the bike. It is incredibly difficult to get your hands on these, for K0 to K6 the pipes are much easier to obtain than for K7 and K8. But i managed to find a set on eBay, brand new replica's which i ofcourse mounted as soon as the engine was in the frame.

Now, i mostly work alone which means i sometimes have no chance to take pictures because i have my hands full, or i simply forget to take pictures as i am too busy. So sorry, no pictures of me mounting the pipes. But here is what they look like when mounted:




Now for the tank; The tank was painted in a horrible red-ish colour that made the entire bike look horrible. Other than that it was in decent condition, no rust and no dents (i thought). I took the tank to the blasting shop and media-blasted the old red paint of. Unfortunately i also blasted away any body fillers that were present to hide a few dents. But overall i was not disapointed with the quality of the tank.

I etch-primed it to avoid flash rusting:


With the rest of the bike now becoming more and more beautiful, the idea of painting the tank myself went out the window, i decided to leave this to the pro's and brought the tank to a local body work shop that i have good experience with. They removed the dents, painted the tank in the original Excel Black colour and applied the sticker. The end result made me drool:




Mounted to the bike it looks like this:


Only thing missing is the gold-coloured Honda logo on the tank. As the black paint around the HONDA letters was mostly missing, i spray painted the entire logo after masking the letters:


The tank with logo's installed:


The bike is now almost done, what's left is the gauge restoration..

[Speedswitch]

Part 10 - Gauge restoration

One of the last things to do is restoring the gauges. As you can see from the picture below the gauge faces have faded quite a bit. There was also rust on the outer cover and on the inner cover. I got new gauge faces from Lecram, and repainted the needle and needle tip.


The speedo needle was also quite bouncy, so i decided to refill the damper pot with 30.000 cst silicone oil. The damper pot of my gauge had no lid, so i figured i should drill a small hole and fill the pot with a syringe. I later sealed up the hole with a tiny amount of hondabond. It works now, needle is steady.


Speedo partially re-assembled and odometer set to 0:


The tacho was also disassembled but i forgot to take pictures of this. It also got a new face-plate and freshly painted needle. The damper for the tacho was still ok, so no need to refill it.


Both gauges mounted:


With the gauges installed, the rebuild is now finished. There was one unpleasant surprise though, i found out the carbs were in bad shape, even though the PO told me they had been rebuilt recently. I ended up taking the carbs apart entirely and clearning every component inside before rebuilding them. After that the bike fired up right away and i took it for a test ride. It runs like clockwork  I will get the carbs synced next week, and then it is officialy finished.

[Speedswitch]

Part 11 - Final pics

These are the final pictures of the completed bike:



All in all i have learned a lot from this project, and i found out that i really enjoy restoring old motorbikes. In fact, i enjoy it so much i bought a second 750K7 to restore next winter 

I want to thank SOHC4.net and its members for being such an awesome place with so much knowledge combined, it has helped me a lot.

[FourUsTry]

Looks fantastic! Would love to see video of it cruising.


I think the US K7 didn't have the front fender stay -- maybe it is that European mix-n-match model thing.


BOTM anyone?

[Sigmund]

Absolutely brilliant build. Well done bothering with all the small details.

[BenelliSEI]

What a fantastic job! To my eye, the K7 and K8 are hugely attractive motorcycles. Good on you for taking the time to get it right!

[Johnie]

Beautiful!!! This was my first CB750 back in the day...pic is the day I brought it home from the dealer. Where did you get the exhaust?

[nvr2old]

It's not often you can go from beginning to end in one fell swoop.  That must've taken a long time to post all those.  As a viewer I appreciate the effort in your detailed descriptions and pics.  The bike looks amazing.  Well done, sir.  Thanks for sharing the process.

[Speedswitch]

Looks fantastic! Would love to see video of it cruising.

I think the US K7 didn't have the front fender stay -- maybe it is that European mix-n-match model thing.

BOTM anyone?

Thanks! Yes, the European K7's did have the front fender stay. There are more subtle differences, like the location of the rear indicators. On US models they are typically mounted to the grab bar under the seat, where on European bikes they are mounted to the tail light bracket.

Absolutely brilliant build. Well done bothering with all the small details.

Thanks! Yes, the details are what makes the whole bike complete

What a fantastic job! To my eye, the K7 and K8 are hugely attractive motorcycles. Good on you for taking the time to get it right!

Thanks, and i agree. Where the original CB750 up to K6 were styled pretty much the same, the K7's and K8's have a much more "eighties" appearence. I like that too. I hope that because of their relative rareness the difference in value will decrease in the near future (as K0's to K6's are now worth about 30% more then K7's or K8's)

Beautiful!!! This was my first CB750 back in the day...pic is the day I brought it home from the dealer. Where did you get the exhaust?

Thanks, and nice picture! I have just noticed that CMSNL has replica exhausts back on stock! These were not available when i started the restoration, so i bought mine from eBay. They were also CMSNL produce but with possible chrome defects (so far not found any defects yet).
https://www.cmsnl.com/honda-cb750k7-four-european-direct-sales_model14391/muffler-assy-cb750k7-non_01800405781/

It's not often you can go from beginning to end in one fell swoop.  That must've taken a long time to post all those.  As a viewer I appreciate the effort in your detailed descriptions and pics.  The bike looks amazing.  Well done, sir.  Thanks for sharing the process.

Thanks! It took me a few hours to get all pictures sorted yes

[BenelliSEI]

Sent you a PM! Voted for you as BOM. Fabulous restoration, full marks for a great looking machine!

[kap384@telus.net]

Just read.  Great to see another '77!

[SKTP]

Looks incredible! Did this bike become a BOTM bike?

[SOHC4 Cafe Racer Fan]

Looks incredible! Did this bike become a BOTM bike?

You bet it was.  It was up for BOTM October 2019: http://forums.sohc4.net/index.php/topic,179294.0.html

[SOHC4 Cafe Racer Fan]

This bike has been nominated (and needs a "second") for Bike of the Month.  Aside from the owner/member, please feel free to post a "second" in the nomination thread:  http://forums.sohc4.net/index.php/topic,180400.0.html

[Shtonecb500]

very nice job here.

[Stev-o]

Just found this thread, what an incredible restoration!  Does not look like the same bike.

I second it...

[desertrefugee]

Sheesh.  Extremely nice work.  My K7 wasn't that nice...even in '79 when this photo was taken!

[flybackwards]

Great work - looks very good. I did the same thing for my Covid stay at home project last winter - here's mine

[grcamna2]

You did an excellent job on your restoration;I especially liked the blasting work done on those engine parts