'74 Honda cb 125S

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'74 Honda cb 125S

Post  abarth850 on Sat 19 Sep - 20:25

not much to see yet, but a topic has to start somewhere.

builders spilled concrete over the forks, barbarians.

I took apart the engine today, I'll give it a light sandblast this week, after which I'll have to decide what to do, clear varnish, polished, black....
the cilinder inside still has some machining marks left, so looks really well for its age.

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Re: '74 Honda cb 125S

Post  martyman5000 on Sat 19 Sep - 22:55

I took apart a motor once (Honda XR75) and had a few extra pieces when I finished Wink

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Re: '74 Honda cb 125S

Post  Luckyboy on Sun 20 Sep - 13:39

Wow is all I can say...
Full marks for bravery...

Good luck on what will a great little machine.

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Re: '74 Honda cb 125S

Post  abarth850 on Fri 4 Dec - 21:37

well, bravery rules!
it took me a while to get the paint on.
the cilinder, cilinderhead and clutchcover are next.
so far, not bad for a first time.



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Re: '74 Honda cb 125S

Post  Gss on Fri 4 Dec - 23:12

Looks good, lots of luck with the rest of the build cheers
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Re: '74 Honda cb 125S

Post  650zed on Mon 7 Dec - 11:34

+1

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Re: '74 Honda cb 125S

Post  abarth850 on Sat 19 Jun - 16:09

The project begins to take shape, some parts are taking forever to arrive...
Since my last update I bought a second cb125 for parts

In much bettter shape than the one I started out with, but it came without papers.
It does however have some things I was looking for, like working speedo, a tacho, and front disk.
It only ran 9900 km in 32 years, the inside of the engine really looked new.

While waiting for the last batch of parts to arrive from thailand, I started work on the front forks, sandblasted the frame, coated the tank inside and put som antirust on the outside.
Hope I can start the build next week, the parts are at Belgian customs office.



The engine has been ready for some time, so long it started collecting dust again


The wheels are the old drumbrake ones, as i am waiting for the rims to be laced onto my new hubs.

new updates will follow soon, as I will be shifting into a higher gear soon.

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Re: '74 Honda cb 125S

Post  abarth850 on Wed 21 Jul - 21:27

Finally got my wheels back,shiny alu rims, so I can continue test-fitting everything.
Exhaust bracket altered to fit the short muffler, made a bracket for the taillights, fitted the battery inside the seat cowl...
By next week I should be ready to take it apart again to paint it





I still haven't made up my mind about the colours (suggestions are welcome)
Also, the lenght of the front fork, still wondering if i should shorten it, but this can always be done later

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Shortening Front Forks

Post  desautdw on Wed 21 Jul - 23:46

You can loosen the top and bottom fork tube pinch bolts and slide them up in the triple clamp to give you a lower look. However, the recommendations I have seen is not to have much more than an inch (about 2 and 3/4 mm) above the top of the triple clamp, but I have seen them higher than this and believe the only problem is if you don't have enough rebound or if it looks funny.
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Re: '74 Honda cb 125S

Post  abarth850 on Thu 22 Jul - 17:25

That would be too easy, but saddly not possible, the top tripple is not a clamp type, the fork tubes end into the yoke with a screw through the yoke. and it does look funny Razz
It has to be lowered (cut) from the bottom, not difficult since I can use a lathe, but without room for error and no way to go back. check the cb50 caféracer on these pages.

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Shortening front end

Post  desautdw on Thu 22 Jul - 18:40

Too bad, is it possible to find another set of used shorter tubes?
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Re: '74 Honda cb 125S

Post  Haakie on Thu 22 Jul - 21:23

You can shorten the inner tubes from below. You can take off as much as you like, and machine new grooves for the circlips. I explained it a little in my topic (Honda CB50 caferacer, the yellow one).

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Re: '74 Honda cb 125S

Post  abarth850 on Thu 22 Jul - 22:50

Haakie wrote:You can shorten the inner tubes from below. You can take off as much as you like, and machine new grooves for the circlips. I explained it a little in my topic (Honda CB50 caferacer, the yellow one).

hint: I'm the one who asked you in your topic Very Happy

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Re: '74 Honda cb 125S

Post  Haakie on Fri 23 Jul - 2:07

Whoops totally forgotten! If you needs some more info you can always contact me!

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Re: '74 Honda cb 125S

Post  abarth850 on Fri 5 Nov - 22:46

I kept saying:" I'm waiting for the wheels to finish my bike". Four months since I got my wheels back, and it still isn't finished, so much for that excuse
But hey, I'm allmost there, everything is working, and it's running nice...right up to 6000 rpm, so I guess I need a bigger jet.
Any advice would be welcome, it's got a 105 jet as standard, I'm running K&N airfilter and a very short, open exhaust. It is bored to 127cc, standard is 122cc.
the red color is a bit darker in reality, the pictures don't do it justice, maybe tomorow I'll take it outside for some more pics





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Re: '74 Honda cb 125S

Post  abarth850 on Fri 21 Jan - 20:12

Sometimes you have to take a huge step back Embarassed
It turns out that a 124cc piston mated to a 122cc cilinder head gives too much compression.
The thing just wouldn't rev, no matter how much I fiddled with jets and spark advance.
Good thing I had a 124cc engine as a spare, so i could try the other head.
I mounted it, guessed the main jet, and it was spot-on.
But since both heads have a different length of distribution chain, one was too long, the other one was a too thight fit.
So now I'll have to build the second motor as well.
I write this as an update on my project, but also as a warning for people building cb125's, as there are some on this forum.
As of now, I'm left with a bicycle without pedals:

And a lot of engine-internals:


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Re: '74 Honda cb 125S

Post  suzukiac50 on Sat 3 Nov - 13:56

The bike looks/sounds great! You can be proud!!

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Re: '74 Honda cb 125S

Post  abarth850 on Sat 3 Nov - 14:16

thanx, 't was a nice visit.
and thank you for reminding me I never finished this topic, which I promise I will.

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Re: '74 Honda cb 125S

Post  abarth850 on Mon 29 Apr - 20:01

What happens when your bike pops into neutral at 9000 rpm? this!



Conrod broke just under the small end, and smashed everything to pieces.
Closeup you can see the conrod



Top view, it broke everything, cases, cilinder, piston.



Good thing I have another engine, hope I get the old one running.
New cilinder and piston already ordered, and no more bigbore for me..

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Re: '74 Honda cb 125S

Post  razzpoutin on Sat 4 May - 13:30

r.i.p little engine,sure ripped open that block
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Re: '74 Honda cb 125S

Post  joolzned on Sat 4 May - 22:44

Thats some engine explosion !!

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Re: '74 Honda cb 125S

Post  suzukiac50 on Sun 5 May - 11:34

Holy sh*t man! I'm sorry for your loss!

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Re: '74 Honda cb 125S

Post  abarth850 on Sun 5 May - 12:41

thanks guys.
time for another one I guess.
just waiting for the cilinder and gaskets to arrive.


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Re: '74 Honda cb 125S

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