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bchrismer's '72 Z50

765 Views 19 Replies 6 Participants Last post by  bchrismer
So, back in 2020, when I joined, I started this thread, to tell a little about my '72, for those of you who didn't see it then. New guy intro - '72 Z50

What was missing from this thread was the history with me and the li'l Honda.

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Now that I have some forward progress going with my '72 K3, and that I weigh well beyond what I did when I was a kid, I would like to use some heavy duty springs in the forks.

When I read the product description on the Fast 50's website, whether it is the springs, bushings, or extended fork legs, their product disclaimer states something like this:

Honda Z50 1992-1999
Honda XR50 2000-2003
Honda CRF50 2004-2023 (we have test fit from 1992-Present Only) May fit other year but we can not guarantee fit yet.

Anybody done it yet who can confirm that these parts would work on a pre-92 z50?


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My buddy in KC power washed it and is getting it into running order for me.
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Thanks, guys!
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I changed the name of the thread to reflect the progress of getting my '72 back in working order.

After looking through the "Show me your z50s" thread, my initial dreams were to do extended fork legs and a 10cm extended swingarm. Since it has always been stored indoors, the paint and chrome is still all in rather amazing shape for a 51 year old bike.

I don't want to stray too far from the original look, so I pulled the trigger on a Tanaka Trading 5cm steel swingarm. This should allow for a better centering of the rear wheel in the arc of the fender. I figure a set of shock extensions should get me back in the right ballpark for the added length of the extended swingarm until I can get a good measurement for some replacement shocks.

I am assuming that swapping the fork springs to a set of the heavy duty springs will take some of the sag out of the front to help level it back out.

Looks like the plans will go like this:

Replace the missing tail lamp lens, grip, and handlebar knob set.
New swingarm, chain, and HD fork springs and Derlin bushings for the first round of mods.
88cc top end and high volume oil pump at a later date.

Not an exciting "build" but it's mine and will be fun entertainment for this old fart.
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Got a text message and some pics today.

"Had a few problems with carb, as you can see. New case gasket is in, new carb is on, put fuel in and the petcock gasket was bad and leaked all over. New one on the way. Still haven't had it run on gas yet.... but it will!!!"

That required a phone call. He is having fun messing around with the little bike. He was able to un-tweak the left handlebar, and even polished up the paint on the tank and side cover.

Sorry for the order that the phone uploaded the pics.

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Thanks @kirrbby

I will be saving all the original parts. I doubt I will ever "restore" it to original based on my history. I have been known to hot rod old stuff.

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The '72 will keep all its stock look, just have a slightly altered stance and a little more power.
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So, being the fool who soon departs with his money, as the proverb says, here's my two "new to me" swingarms. The top one was an original '76 that I bought on the Ebay with the intention of having a buddy add some extension to it. Then, after considering the cost of sandblasting and powdercoating, decided it was just a better solution to buck up and buy the Tanaka Trading black 5cm extended swingarm. I figure I saved myself more money doing it this way than the cost of his time and the powder coating costs combined, plus it will allow me to run my stock chain guard and it came with the extended rear brake rod.

Now I just need to get a factory sticker for the right side of the swingarm to help pull off the "stock" appearance.

(Oh...and yes, the photo location is in the bed of the 1940 Ford Stake truck shown above, that still has all the factory wood for the bed floor and stake sides)
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You should be SURE to keep the original carb.
Dan, the guy working on the bike, did buy a rebuild kit for the carb, but chose to stick an aftermarket carb on it to get it running. I think he said he had more money in the rebuild kit than he did for the "substitute" carb.

He was trying to get everything working so he could bring it to a car event we are both attending this weekend, which was the other reason for the "substitute" carb. Since he's waiting on a new gasket for the stock petcock, rather than installing a replacement, that delayed everything.

He did advise me that he put the stock carb, air cleaner, and carb kit in the box and did encourage me to soak the carb and rebuild it once I got it back home.
Digging what your'e doing. Looks like a great bike to start w/. Keep posting up what you are doing. We all like pictures. Like the cars too.
Thanks! I'm sure that there are some who think I am nuts for not just doing a "restoration" of the little bike. I think the plans that I have won't take away the character. If I were swapping the forks, putting an aluminum 10cm swing arm, and swapping a 140cc pit bike motor, a custom paint job, and a drag pipe on it, then I would also think I am nuts, too.

I figure whenever I decide to do the 88cc upgrade, if I paint the outside of the cylinder black, most folks wouldn't notice it unless they looked on the side of the head.

Just a fair warning, my brain gets obsessed with the "planning" part of projects. So much so that I usually start out with a spreadsheet and instead of just keeping track of where my money went, it's trying to figure out math problems to get the results that I have pictured in my brain.

An example of this obsessive behavior was choosing a manual transmission for my '40 Ford coupe, based on the rear end gear ratios, RPMs at take off and shift points, and the resulting RPM points after the shift has been made, just so I know what to expect when it's time to drive them. Turns out sometimes that works perfectly, and in the case of my '40 Ford panel truck, it resulted in me needing to change the rear gear ratios to get the RPMs in a range that shifting from 3rd to 4th didn't drop me below the power band of the 85HP flathead.

Today's mathing problem involved a z50 that's in KCMO, me in Springfield, a measurement from a stock and a 5cm extended swingarm, and an educated guess of the stock shock length of 280mm. (I HATED 8th grade geometry, and don't remember much, so I am thankful for online calculator tools for stuff like this.)

I actually kind of already knew the answer from having read a BUNCH of threads on the topic, so the answer is 12 to 12 1/2" or in the neighborhood of 305-315mm, but I had to solve the problem for myself.

Keeping the angle from the swingarm pivot to upper shock mount the same, results in needing the longer shock. It also will result in a slightly raised back end of the bike without any rider weight on it, which I am definitely a fan of since I will need that room since I am now a long time member of the "Tenth of a ton" club.

By using the protractor on the image of my z50 sitting in my driveway, I was able to calculate the approximate angle from the axle to the swingarm pivot, and up to the shock mount.

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Using the known length of 280mm shock, and the 9" between the shock mount and pivot bushing center, and the 73degree angle of the swingarm to pivot and upper shock mount, it gave me a measurement for the distance between the upper shock mount to the pivot bolt.

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I was able to change the formula to use the extended length of the new swingarm, and it gave me a measurement of 311.

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The result of this? Well, I chose to spend some Amazon credits on a pair of 1.5" shock extensions to see how my maths prove out before dropping money on the final shocks that will appropriately support my lard butt. LOL

(Oh, and just for funzies, the bottom of the triangle should be pointed down at about a 21 degree angle to make it look right.)
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NERD ALERT --- uhhh lost me with all the math. I too wasn't numbers oriented either. Post pics up when "shock extensions" arrive - curious as to what you're doing.
LOL! That's why I put the NERD ALERT notice at the top of that post.

I just figured I'd help paint the picture of my mental condition that gets a little out of control into an obsessive state. My hot rod buddies refer to me as the wheel and tire guru because I obsess about trying to fit the tire so it is visually appealing into the fender opening space on pretty much everything I have.

To me, a stock z50 looks wrong as the arc of the fender is about 2" past the arc of the rear tire, which is why I am choosing to "fix" that visually.

@bsdoig posted a pic of his ruby red '72 with a 5cm extended swingarm and that helped me make my decision.
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Just got a text message from Dan.

"Update on scooter!!!!
It does run on gas with original carb! I let it warm up a bit and decided to se if it would ride. For whatever reason the clutch does not disengage, and it won't stop in gear. I need to pull the side cover back off and see what is what in there. Haven't kept you caught up for a bit, still playing with it!!!!!!"

I told him that I had never adjusted the clutch, so the plates are probably the originals. I also told him I am planning on rebuilding the clutch with heavy duty springs. Knowing Dan, he may take the liberty of doing that while he has the clutch cover back off.

I'm hopeful that he can find a ride for it when they come down for the street rod nationals next week.
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So, it's been so long since I have ridden the li'l bike that I can't remember if it should roll while in gear and not running, or the clutch requires the inertia of the engine running to disengage. Dan says that his CT70s will roll when they are not running but in gear. He says my 50 drags the rear tire if he pushes it in gear while not running.

Latest text from Dan:

Back on the operating table, it shifts all three gears with the clutch basket off, so problem must be in clutch area. The shift actuator has separated and bent, so does the clutch kit you're looking at have the actuator parts with it?

The clutch plate ring has got some wear on it from the rollers.
That's all I've found so far!

So, I called him up and we talked through the clutch issues. He did say that he fired it up and rode it around on his second attempt. He said the first attempt it got away from him and left him sitting on the driveway. LOL

With all the wear on the clutch internals, I wound up placing an order with TBParts for a new HD clutch, the high volume oil pump, and the 88cc + carb kit, and an order with CHP to get replacement parts for the actuating stuff, and a new set of grips to replace the missing one and make sure they both match.

I asked him if he wanted to just box everything up and bring it back and I could do the rest, and he offered to let me just ship everything to him and he'd have fun doing it.

In hind sight, I think I probably should have added larger front sprocket, but failed to do so. It would be a great time to do that since I have the +5cm swingarm and will have to replace the chain.
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Pretty much an empty post other than to say that I know that all my parts got delivered to Dan's house over the weekend while he was hanging out down here in Springfield at the NSRA MidAm Nationals playing cars. We did talk "scooters" as he refers to my lil bike, and he said that he had the head loosened up and ready to come off to work on when he got home. That'll be the 88cc setup and high volume oil pump and heavy duty clutch. I didn't send the swingarm with him, just mainly because I forgot to, but at least that gives ME something to do once I get it home.

But for now, I sit and wait with great anticipation for his text to tell me about how much fun he's having riding wheelies on it.
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