Z50 k0 build

Picked up this bike along with a k1 for 100$ each last November. I rebuilt the k1 first, and spent a good portion of the year on it. I learned alot and made most of the usual mistakes.

The bikes spent their life in the central valley of California on a farm, and probably taught a few generations how to ride. It looks like most of the welding hacks were to keep the bike running. A stud welded to the frame neck in front of the tank, and the usual welded up kick starter.

Pretty much the only salvageable parts are the frame, hubs, motor, carb, handlebar holder, and trees. The rest of the parts are going to have to be sourced which is going to take a lot of time and effort and dollars.

I started with the motor tear down this weekend. Again, I'm not sure what kind of life that had but it sure seems well-used. The tear-down went pretty smooth especially with a torch and impact driver.
I'm not sure exactly what killed the motor but it looks like when it did stop, both valves were closed because the piston was at top dead center and there was not as much damage on the Dome side of the head, and no pitted rust. Another thing that looks like it may have stopped the motor is the shift star was loose without even touching it, either that or the missing Kickstarter meant that the bike had to be bump started.

There wasn't any oil inside the engine just a ton of white residue and rust. It makes me wonder if the motor was flushed with fuel or some sort of solvent that left a white residue. The residue is similar to what was in the float bowl of the carburetor.

The disassembly was pretty smooth, and after seeing the damage I didn't have to bag nearly as many parts as on the other motor simply because they were basically just trash. One of the more difficult parts was getting the clutch cover off. Even though there wasn't a kick-start shaft what was left was bent just enough to make it impossible to get the clutch cover to slide off. Luckily it wasn't an early enough serial number to have a z 50 m cover. So I had the fun pleasure of cutting up the cover just to get it off.

Pretty much everything inside the engine is junk. I wasn't able to check the end play on the connecting rod because I think there's too much rust in there, and I haven't checked the shift forks either, but I will before I toss them just to see how worn everything is.

The case is going to need heli coils for the footpeg mounts, other than that it just looks like it got chipped buy the shift drum plug probably from when a chain exploded.

One thing that I did notice is that on the oil pump they used Big 8 bolts where on my Z50 K1's they used screws for the oil pump. The flywheel also seemed to be a bit different on the outer shape too.

I'm going to send the head out for new valve guides and vapor blast along with the cases first.

Ill post my progress. And plenty of pictures. I know you guys like alot of pictures.

Where does this motor rank on the scale from 1-10 in the house of horrors? Is it getting hall of fame consideration?

More pics

Aaaaand more.

Tripod said:

Where does this motor rank on the scale from 1-10 in the house of horrors? Is it getting hall of fame consideration?

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At this moment I’m filled with gratitude that the motor on my bike doesn’t look like I found it in the bottom of a saltwater aquarium. ☠️

You shoulda saved those pix for Halloween

I don't see much in that lower end that's even salvageable. You might have to beg the scrapyard to take that pile of rusty/oxidized .

The head and cylinder should be restorable. I usually don't recommend wet blasting aluminum parts on these bikes. That said, when a head casting is that heavily oxidized, on the outside, the unnatural (but very nice) post-blasting appearance can be the best choice. As for the case castings, it's too hard to tell the actual condition from photographs. You might be better off with walnut shell blasting, followed by chemical cleaning. There appears to be a chance of retaining/restoring the as-cast surface appearance, which matters on an early hardtail. If you do have the case halves wet-blasted, leave the ball bearings place, to shield the seats, and use the transmission shafts to protect the bronze bushings during the process. You'll have a lot of surgical scrubbing to do, afterward. That blast media is harder than metal; a few stray granules could cause heartbreak. Pay attention to the oil passages, top end metering orifice and any blind holes, such as the stud pockets. They should all be cleaned with small brushes.

Im finally getting around to posting some pictures of the rebuild. Nothing fancy, looks just like all the other motors.

I elected to have the head and cases vapor blasted. Not concourse correct, but im not worried.

EVERYTHING from inside the motor went into the trash. I mean i saved it, but still. I think the cylinder may clean up with an overbore, but thats a someday project.

I kept the shift drum retaining bolt, the oil pump bolts, and the shift star.

Well done ! Looking good.

That is a huge difference! You actually turned a boat anchor into a 50cc engine.

That looks very nice. Impossible to know, now, how it might have turned out using less-invasive cleaning methods. Judging by your "before" photos, the oxidation looks like it was too severe and pervasive...one of those relatively rare instances where wet-blasting w/hard media was clearly the best choice.

@Tripod what's the status of this project? I've been mining Z50 rebuilds and wondered if your project is a roller now?

airblazer said:

@Tripod what's the status of this project? I've been mining Z50 rebuilds and wondered if your project is a roller now?

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Ive been collecting parts for over a year now. Im pretty much down to finding a set of fenders. Ive debated just using oem k1 fenders and being satisfied that they are chrome and still Honda. I've also debated on getting a set of repop k0 fenders off ebay...from Vietnam.

I have the left handlebar but no right handlebar. I'll probably just pick up an oem right but then the chrome will be much better on the one side. So then if I need to rechrome the left bar, i might as well just throw in the muffler too.

Good k0/k1 gas tanks are near impossible to find. The ones on ebay still are a gamble as pictures only tell so much. Especially about pin holes in the bottom as well as the fuel tap. Seems like 99% have handlebar dents. Tons of k2 tanks can still be had though.

Im going with repop grips and levers. The levers i have found im still leery about whether or not they are honda or just repops. Too expensive to take that risk. As for the chain, ive run across a few 415 sprocket sets, but as the project drags on, im not going to get a 100 point resto, so a 420 set off a k1 will be good enough. And far cheaper to source.

Ive been working on sanding the hubs and plates. Its one of my least favorite tasks. They are however k0 hubs front and rear, so worth the hassle.

I'll probably send it out for paint this summer. I keep finding other projects.

I recently seen a set of nos K0 fenders on eBay. How much are you willing to spend?
I have a K0 tank, but I don't recall what condition it's in.

Somebody bought those fenders in the last 30 minutes. Was it you @Tripod ?

airblazer said:

Somebody bought those fenders in the last 30 minutes. Was it you @Tripod ?

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No not me. Im hesitant to buy something that expensive from overseas.

I have another k0 motor sitting around. Its actually only about 30 numbers off from my frame. I think this other motor in the original post is about 140ish, but original/born to the bike.

I picked up a front and rear fender set off ebay for 25$each. It was a real gamble on my part in hopes that it would be a k0 set. In my excitement i didnt notice the rear fender had been shortened, thus the missing tailight hole.

I just now stripped off paint from the front fender top and bottom. It might be wishful thinking, but the primer on top is very difficult to cut through. Similar to what ive been dealing with stripping the flywheel covers for paint.

The bright chrome from this era isnt near as nice as triple chrome. The red fender is what i hope is k0. Its pictured next to my k1 fender to see if there is a difference in the hopefully bare steel and bright chrome.

I have a feeling that to keep costs down Honda only chromed their parts- no copper or nickel. I got NOS bars for my k1 back when they were cheap, I think the right hand one was not even polished before chroming,it has a very brushed looking finish. Maybe I'll have them redone someday but unless you look close it's not bad. Be careful plating the muffler they tend to buff off the verbage on them
Two things to think over how about repro chrome fenders- send them out and have a plater remove the chrome, weld up the taillight hole and paint them? How about a repro tank,I bought one of those out of Tampa. I haven't spent much time looking it over,it's not perfect little wavy on one side but nothing bad and the front mounts are too straight up and down,I plan on removing them and rewelding them to copy my original. Better than trying to repair an old beat one.