1975 CB550 K Rebuild & Minor Mods


Been Around the Block

I've just gotten a hold of a project bike. 1975 CB550 K, 16000 miles on the clock, motor is locked/seized, the bike as a whole is in pretty rough shape, but I think it has plenty of potential. It's a project to keep me occupied whilst I go through recovering from some health issues, something I can work on when I'm well enough to do so. I'm not yet sure given my health, and experience, whether I've bitten off my than I can chew, but I figure whilst I can still bite, I'm gonna get to chomping. That said, I think it'll be a slow moving thread, so bear with me. It's my second bike, and before I got ill, I worked with CNC machinery, so I have OK mechanical skills.

I've spent some time reading up on the manuals, and other posts on here, so I have a bit of a game plan together for now.My plan is to restore it as much to stock as I can, given availability and price of parts. Hoping to focus most of my efforts on getting everything mechanical correct, rather than major atheistic changes. Plus I think these bikes look rad stock.

Today I started stripping a bit of it apart. Took out the spark plugs. The plug on cylinder 4 wouldn't budge, even after a soak with WD40 and oil. Hoping its just rust, and not cross threaded. I figure since I'm planning to pull the head off, I'll play it safe, and not force it for now. I sprayed a some WD40 down the other holes.
Cleaned some of the chrome parts with foil and water, most of the rust seems to be on the surface.

From what I can see under the gaiters, there isn't any rust on the stanchions, which is a win.

So here's some pictures. Any thoughts, info, advice etc would be greatly welcomed.

Before stripping it.



It has taken a fair slide down the road at some point, from the looks, it was never ridden after that. From what I can see the frame and forks look straight, the handle bars, brake pedal, head light, stator cover and exhaust took some damage.


Some wasps must have called the bike home for a while, this was under the tank. One of the wasps (deceased) went down with the ship, and is still in the side of the carb.


The tank is a fair mess, and needs taking back to bare metal and repainting. I'd really love to keep the original colour/paint scheme, but I'm not sure whether or not its going to be achievable. I've seen some threads about how to redo the metal flake plaint, but I think it's beyond my setup.
There's a decent ding in one side, that I can't pop out. So not sure if I'll just have to fill it yet or not. The inside is pretty rusty. I am planning to clean it out with vinegar, then flush with bicarb and water. It's rusty along the exterior bottom, under where the chrome trim was, there is some bubbling in the paint, but can't really tell if its caused by interior or exterior rust. Not sure if it might have any pinhole leaks. If I clean it back to bare metal for repainting, and fill it will fuel, will any pinhole leaks be noticeable? Then if there is any leaks, I'll reseal it.



Under side of the tank looks OK, just some light surface rust.

Side cover needs replacing

Personally I love the look of the 4 into 4 exhausts. Unfortunately the right upper pipe has a gaping crack in it, probably from the crash. So I'll have to try find a replacement, which in Australia might be quite expensive. Otherwise I'll have to rethink it.


I opened up the master cylinder, and its filled with what looks like sawdust...I'm not sure if brake fluid over time can deteriorate like this, or if its got water in it, or if its eaten away some seals or something. Anyone ever seen this?

That's it so far. If you have any thoughts or advice, please let me know. Cheers!


Coast to Coast
Re: 1975 CB550 K Rebuild & Restoration

Wow. Are there any usable parts on that thing? I'll watch, but I'm thinking you may be better parting it out and buying something that runs and can actually be used. Did you get a title? Not trying to be a dick, but your going to have to replace so many things on that bike just to make it safe to ride and thats not even getting into the engine.


Been Around the Block
Re: 1975 CB550 K Rebuild and Minor Mods

Bit of an update. Changed the title slightly for anyone who may concerned with such things, as I wont be doing a full restoration. I have decided on a few small mods, but nothing major.

Firstly RE:Inceptor. Thanks for stopping by. I can see your point, but I suppose to be clear, I bought the bike with every intention of a full rebuild, replacing wheel bearings, brakes, steering bearings, motor internals etc, and what ever else showed up on the way, within reason. Yes, its a fair mess, but the majority of the parts are fixable, given time, which I have no limit on.

So I started tearing the bike apart. Took of the fuel tank, and removed the petcock. I then filled it with vinegar, and let it sit for a couple of days. Then flushed it with with water and bicarb, then flushed it with methylated spirits. All the rust was gone, but there was still some varnished fuel. So I filled it with nuts and ball bearings, and some acetone, gave it a good shake, and am letting it soak for a few hours. Ill post some pics when its done.


Pulled apart the master cylinder. Took a fair bit of work and patience. Firstly the circlip ends snapped out, which was great.... :mad: Got that sorted and started getting the piston moving, or so I thought. Instead it sheared in two. :eek: Eventually go the other half out, along with the springs and seals. The bore looks good, no scoring.
Also tidied up the master cylinder cap, and gave it a paint.


Stripped all the wiring, fenders, lights, gauges, etc. Cleaned some of the chrome as I went.Some of the chrome still has pitting, not sure if ill be able to get it all out. So might possibly work the chrome back until it looks like brushed.

Drained the oil. Ran a magnet through the pan, and then poured the oil through a cloth to see if the was any metal shavings, it was all clear. Removed the sump, and there was only a few small specks on the pickup.

Removed the airbox and battery box. Then I pulled the carbs.

Removed the front end. Forks look OK. There is the usual rust on the tubes under where the headlight ears were, but nothing in the area of travel. Rolled the stems across my workbench to check they didn't have any major bends, they look good, now need a good clean.

Removed the triple clamp and the stem head bearings races, the plan is to replace with tapered bearings.

Took off the rear wheel and brake linkages, then rolled the bike over onto its side, and unbolted the motor mounts, and lifted the frame off. I then knocked out the swingarm pin, it looks to be in great condition, there was no play in the swing arm. From what I’ve read, there is short bushes either end of the swing arm, I can’t really tell by looking at the inside. I assume a blind bearing puller would be needed? They usually get changed over to bronze bushes?


Made up a basic engine stand and started tearing down the motor. Had to wait for a impact screwdriver to come in the post, because those screws weren't going anywhere without a some persuasion.

Removed the head covers. Then went about removing the head. Due to the engine being seized, getting the cam sprocket bolts undone was a bit of a pain, but after grinding down a spanner, it was all out.
The cam followers, and cam journals all look to be in great condition.


The cam has some pitting on the leading edges on most of the lobes, but from what I've read this isn't too big an issue? Anyone got any advice or experience? I think they look worse in the photos, they're quite shallow, I'd say the pits would be 0.2mm or so max.


Cam chain guide and tension. Do these look ok? Doesn’t seem to be much wear from what I can see.


The spark plug on cylinder 4 was extremely tight. It did screw out, and surprisingly wasn't cross threaded, but it looks as though a couple of the threads are damaged. I'll trying running a tap down the thread, when I get one the right pitch. I don’t think it will need a heli coil.

All the gasket surfaces look good, no noticeable dings. The pistons seemed to be stuck to the walls, so I poured a mixture of diesel, oil, and a dash of acetone on top, and let them sit for a couple of hours.

Got the jugs up off two of the pistons, but was still stuck on the other two, so left it to soak overnight. From what I can see of the cylinders, there are no marks, or scoring. :D


Thats all for now, hopefully get the jugs off tomorrow, and see what the pistons and bottom end is like.


Been Around the Block
So the pistons proved to be a little more stubborn than I initially anticipated, but I guess that was my first mistake, as expectation is the mother of all heartache.

So I'd left the pistons to soak with diesel and oil. Next morning tried to move the jugs, no dice. Grabbed a rubber mallet to give it a light tap to see if it would move. Tried this gently for a while, no luck, and instead I ended up chipping one of the fins. Grrrr :mad: I'll should be able to cold weld it later though.

Put the hammer down, and thought I'd try to work a little smarter. I had the jugs raised off the base a little, so I put a ratchet strap through under and around the jugs, then hooked it up to the rafters, to see if I could could get gravity and the weight of the motor to do the work. Still no luck. Decided that heat was going to be needed. Unfortunately no longer have the oxy-acetylene setup, so I had to improvise with a method I had seen on SOHC4.

Again I left the pistons to soak in some diesel and acetone. Did some reading and found acetone and ATF was a proved penetrant. Didn't have any ATF, and it was a public holiday. Did have acetone, 2 stroke oil and hydraulic oil. So I made a 50/50 mix of acetone and 2 stroke oil, as I read the rust inhibitors in 2 stroke oil can be helpful at breaking stuff free. Poured some in each cylinder. Then I made a wick from some rag dipped in acetone, and lit it up.


I did this about four or five times, getting it to move a little each time after it cooled. I was able to get the outer two pistons free of the sleeves, and ascertain that the bottom end was OK, and the crank could turn. So I greased the cylinders, fitted the pistons back in, fitted the head, and then gently rocked the crank back and forth with a socket on the stator bolt, and eventually got it to come free.


I had started to wonder what condition the cylinders might be in, that given how frozen it was, there might be some serious rust pitting, but thankfully I was pleasantly surprised. :) There's one tiny bit of very light surface rust on the #3 cylinder, which was the problematic cylinder, but the rest looks like a hone should do.

The pistons need a good clean, the wristpin on #3 is a bit stiff, so next I'll take them off and clean them up, and see what shape they are in.



Gold Coast, Queensland
I am going to watch this, good to see someone else bringing back a "junk" bike.


Been Around the Block
Nothing too exciting to report, started back on treatment, and am feeling pretty average, so I have just been working through some small bits and pieces. Also I discovered the Ichiban Moto thread, so that has chewed up a few hours.....

Ordered some parts, so waiting on them to arrive.

Another ghetto hub retainer tool and valve spring compressor were born. Got the retainer out fairly easily, thankfully. Threads seem all good.



Weather has been good, so I thought I'd get some painting done before winter sets in.

Soaked the foot pegs mounts in vinegar overnight, was surprised how clean they came out. Then just hit them with a wire brush. I've cleaned up and primed the centre stand, side stand and footpegs mounts so far.

Cleaned 90% of the frame with a wire knot wheel on the angle grinder, then tried out the DIY sand blaster for the unreachable parts. It's slow going with the compressor I've got, but it works OK.


Been Around the Block
On your swingarm-
When you pop those dust caps off the ends of it, you should be able to knock them out by hand with a drift and a hammer. But it will be easier to see in there when you take those caps off. They are probably cemented on there with old petrified grease, but they just sit on the swingarm. And yes, upgrading the bushings to bronze bushings or needle bearings is a great idea!


21 years young, 1972 Honda CB350.
Awesome! I love to see people restore things that most would say isn't worth it. Keep up the good work!



Been Around the Block
Excellent work. I'm looking forward to this thing coming back together. As a fellow Aussie, I hate how anything motorcycle related that's over 20 years old is made of gold (or so says the price).



Been Around the Block
Finally got the front brake piston out. After having soaked it in boiling water, I ended up having to remove the nipple fitting for the gun and screw the arm straight into the caliper. The piston looks pretty fingered, it has some deep pitting, so I'll be replacing that. I think the caliper looks OK, there some pitting on the aluminium, which I cleaned up with some fine steel wool. It feels smooth when I run my finger around it, seem only to be light surface aluminium oxidation.

Pressed the piston pins out using some 1/4" threaded rod. I found a piece of copper pipe, slightly bigger than the piston pin, and it was just the right size to fit into a 18 deep socket. So I cut it a little longer than the socket, pressed it in, then flanged the ends so that there was a copper cushion between the socket and piston, as so not to do any damage. Worked pretty well. Pistons are now soaking in some diesel.

Used another piece of the copper pipe to make a gasket scraper, that I'd seen on someone else's build. Kept a file handy to keep it sharp. I had already tried razor blades, and after an hour had made no head way really. Between the copper scraper and some carb cleaner its coming off pretty well. Hoping to clean it up the gasket, then soda blast the rest.

I gathered some bits and pieces so that I could zinc plate some of the hardware. Works OK, little bit inconsistent so far, I think its because of the temperature. Am going to buy a aquarium heater from eBay and see how it goes. Heres the rear brake arm after plating.

I left the front sprocket cover to soak, hoping to get some of the layers of grease out. Unfortunately to my stupidity, I had it soaking in sugar soap, which I did not realise was highly alkaline, and it ate into the cover. :mad: Well atleast I found out on a side cover I guess.

I pointed a couple of allen keys to make some basic vernier extensions, so that I could check the cylinders for roundness and taper. The cylinders look good. My flex hone just arrived, so once I've soda blasted, I plan to give them a hone to break the glaze, and see what size that are before ordering pistons/rings.

At this stage I'm planning on splitting the cases, to give everything a good clean. It's a bit daunting to be honest, anyone got any tips/ suggestions for me? Ive got both the Honda Service Manual and Clymer, so hopefully that will see me through.

I just ordered some Threebond 1104. Can anyone tell me if I'm wrong, but do the cases halves have no gasket and just sealant?
I was thinking of using Permatex Copper spray for all the other gaskets. Or would it be better just to use a light coating of 1104 everywhere?



Been Around the Block
After some advice from some other members, I've ordered a set of CB500 +3mm Oversize pistons and am going to have the cylinders bored to match at 59mm. Thanks for the pointers guys.

I kept working through, and split the cases.

I've read that the primary shaft can be removed by threading a frame bolt into the shaft and using it as a slide hammer, but I've had no success yet. What am I missing?

All of the gears and dogs look OK. The selector forks seem OK.

My cases are stamped BBAAA

The rods are marked "2" on one side and "D" on the other.


Cant see any markings on the crank, apart from this which sort of looks like and "N" with an arrow.

All of the journals in the cases that I can see so far have some shinning, but are smooth.


So I was hoping someone might be able to help me understand what clearances I need to be looking for, when I plastigauge the crank journal bearings, and the rod big end bearings. I am a bit lost trying to understand these table to be honest.
These are the tables from the Clymer book I have.




Also, what do people suggest with the main seals, are they re-usable if they look OK?

So that's where I am at, any advice or info that would help me out, so I can get this build done right, would be greatly appreciated!


Been Around the Block
Got the primary shaft out, just took a little more force, I used so larger sockets as the slide hammer.

Theres a little bit of marking from the primary chain. Thoughts? Does this warrant replacing the primary chain?


So when my plastigauge arrives I will check the camshaft main bearings, and the rod big end clearances. The Clymer manual states, if the clearance is above 0.08mm on both sets, then they must be replaced.

Some of the camshaft journal bearings have some scratches, and I assume they must be replaced. Is it possible to replace 1 half, or do both halves need replacing? Some appear to have what looks like pitting, but are smooth to touch. Any thoughts?



Staff member
Wow - I didn't realize you were tearing it down to that degree. Good for you checking everything over.

I don't think you need to worry much about the bottom end or cam shaft journals. These things are designed to be beaten to death and run hard. Don't overthink this rebuild or you'll spend thousands on the engine and have wasted the money.


Been Around the Block
Well, I felt for getting some much needed experience, and for piece of mind I should go all out.
One of the guys on SOHC also said that the bottom ends are fairly strong in these motors, so I'm planning just to check the clearances with plastigauge, replace the primary chain ( as it's rubbing the cases), new cam chain, and possibly new cam chain guides, undecided on that one yet.

Then hopefully it'll just need a thorough clean and I'll be able to seal it back up.


Been Around the Block
Got around to pulling the rods off the crank. All the bearings and journals look good. One set of bearings has a slight bit of oxidation from where it sat on the oil hole.


Measured the clearance of the bearings with plastigauge. Cranked the nuts to 20.5 Nm, and all the bearings measured at 0.038mm. Specs dictates that they be below 0.080mm.




Worked through and checked the clearances on the mains, all of them checked out to be good. Ran them at 23Nm/17 Ft/Lbs, and they all measured in around the 0.038mm mark, so that was good news. Tolerance is below 0.080mm

Cleaned the top half of the case, and painted it, now just need to do the same with the bottom half, and clean up the threads.

Just got cylinders back from being bored and honed to suit the new pistons.

Not sure how this happened, not too happy about it though. It wasn't there when I left it with him. This likely to cause me any headaches?


Got some of this to use on reassembly. This motor is likely go to sit for +6 months before being run. I've read this stuff is good on mains and big ends, should I put this on the gears in the transmission, or are they better with a coating of oil? Or can the assembly lube go on anything?

All going well, should be able to seal it back up once a new primary chain, cam chain and seal kit arrives.


Been Around the Block
Have made a bit of progress. Checked the clearances on the mains, and they were all well within spec, all were around 0.038mm.

After a lot of cleaning, some painting, the cases are back together, sealed up with Threebond 1104. Here's hoping they are sealed up OK.

Everything seemed to go pretty smoothly. New primary chain and cam chain installed. New seal kit installed.
Reassembled the cases upside down. Ended up installing the primary drive gear in the chain, and left the primary shaft out until after the cases were sealed. Left it in the freezer for a few hours, took it out, lined up the needle bearings, and in it popped.

Bought this oil seal kit from eBay. Seals were good and supple, not bad for $25 delivered. Just doesn't include the main shaft blanking plug seal.

Next up hopefully I'll be fitting the new pistons and cylinders.

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