Build of a Honda CB125S (DIY Digital tachometer)

Hey

I have just bought an old Honda CB125S (1974 i think).
i know that maybe a bike like this is maybe to "small" to make a cafe racer from,
but its my first time i do something like this an i want it to be possible.

as u see on the pictures i have to take it completely apart and paint it.
then restore the engine. and i am going to re do all the electrical wiring.



but the first thing i have to find is an contact switch for the bike and the gas thank.
of course i only want one key for, any idea's on where i can find that.

Re: Build of a Honda CB125S

Good to see another CB125S! The '74s had a mechanical front disc brake. There should be a plate on the steering stem with the year on it to be sure. What do you plan on doing to it?

Re: Build of a Honda CB125S

I'm watching.

I have a 72 CB100, I'm working on, so maybe, I'll be able to give some insight.

Re: Build of a Honda CB125S

I have looked on the frame and the engine, the numbers are different.
frame: 1151553 (CB 125 S)
engine: 1179017 (CB 125 SE)
and on the exhaust there is written: hmcb125S

so i don't really know from what year it is .

I was planning to completely sandblast everything, and paint it again. (don't know the collor yet)
an completely renew the electrics.
and give the engine a complete overhaul.

Now i have it at home, here are some additional pictures:

Re: Build of a Honda CB125S

It looks like a '73 to me based on the external spring forks, the gas tank cap being offset to the right, and the lack of a tachometer.

When you renew the electrics are you going to switch it from a 6V to 12V system?

Re: Build of a Honda CB125S

Looks like an awesome start man!

Re: Build of a Honda CB125S

So Yeah

it has been a long time :-*

i haven't done allot, but easy does it.
i was sanding down the tank and i noticed that it went so slow and it would cost me a fortune on sandpaper,
that i thought, lets just make a sandblaster.
so that's what i have been doing now.
there is a pic of the design and a pic of the build now (done today).
as you can see, it is more than big enough, maybe i can also make it a small spray booth, but i have to think about it.

I think i will have it done this weekend or the next.
I only have to find a compressor a gun an some other small parts.

and found a nice material to put around hoses and wires that otherwise wood be ugly, its called Gremflex,
but it probably has many more names. i will post a picture to show the effect.


And about the 6V to 12V. i think i am just going to keep it a 6V. i have already bought a battery.

Re: Build of a Honda CB125S

So i have been doing some actual work now.

things i had/ have to do:
- paint some stuff
- paint the gas tank
- overhaul the engine
- make/ search for a new seat
- electrics (i have kept the 6volt system)
- ....

1) painting some stuff
i had to paint the head light, and "top plate"? (i don't know the name).
this is done with normal primer, normal spray paint, and normal clear coat, so i suppose i will have to redo it with
a 2k clear cote once?









2) Painting the Gas tank.
for this i have chosen for a black/Gray, with a racing stripe (but i consists of the 3 Jamaican colours)
i wanted to do the army green to, but it isn't really unique.
I think that allot of people will link this with hippie's or pot smokers but i just think that it are some
fun colours to use. here to have i used normal spray paint primer, normal spray paint, but no clear cote yet.
so i have to but a can of spraymax 2K clear and finish it. will it actual be a problem if i use normal primer(1K)?










the stripes had to be redone, because i had use bad tape.







as u can see, the clear coat is still not done.


how it looked like 2 day's ago

3) The engine
i had to redo the valves because they where bent.
and all was fine, it was running fine. but the al of the sudden, the kick start didn't want to engage.
so i have to reopen the engine egain, euugh

i have dissembled it a big part, an what have i seen
the valve adjustment screws where just gone. one was sticking on the flywheel
and the other one i haven't found yet.

now i have to open the crank case, and again, have to spend up around 50-100 Euro's for tools,
just to be able to find the problem.
and like today the kick start works again. but i don't want to take the chance.

when it was running fine:


and now:



i have also found that the clutch adjustment screw in the clutch cover is broken.

4) just a question
does anybody know for what this is for, its a coil on the fork?

Re: Build of a Honda CB125S

and a little video: http://www.youtube.com/watch?v=VvcIEk9Agcg&feature=youtu.be

Re: Build of a Honda CB125S

Just a picture of the gas tank with clear coat

Re: Build of a Honda CB125S

Amazing build so far, mate!

And the color job is great too.

Re: Build of a Honda CB125S

Awesome. Keep it real. Love the head light/ speedo combo.

Re: Build of a Honda CB125S

Okey so it has been so long since i posted something.
And i have not had a lot of time, to really finish it.

BUT i am adding something new to my bike,
Because Honda started to include RPM gauche from 1974.
i am gone make my own.

and i am gone do so, from a Micro-controller, counting the pulses from the spark plug.
And then showing them on an screen. and from then on, my fantasy went a bit crazy ..
I am probably going to ad: Voltage meter to it, maybe a security, ..

probably going to make a car computer, or whatever it is called.
Here is a picture of the electronics needed, and the screen i salvaged from an old pc
here i can show that i have a message, an i can show the gear i am in (not sure how to do that).

Re: Build of a Honda CB125S

The micro portion will be interesting to watch! What micro are you planning to use?

Also, the "coil" on the triple is a hi wattage resistor. Can't remember what it's for but a schematic will tell. Anyway, it's on the front to keep it cool and the metal cage is a heatsink. You might be able to remove it by going 12v. Lots of info to do that.

Re: Build of a Honda CB125S

So, some big progress.
I got my bike running like a charm this weekend, i always tought my carb was broken or something.
but it was just my float level that was of, and this because of a bad carb rebuild kit :
i will post a video if anybody wants to see it...

Ideas for the program:
For the RPM gauge, first i wanted to count the amout of sparks in one second, but then i came to the realization, that the update rate would be to slow, and not smooth.
SO i am just going to count the amount of time between two spark pulses
and this every half second or so (will decide this later).

Probably going to make a "bar mode" and just the rpm number.

The hardware, measuring a spark puls
Idea 1
The original idea here was to take a puls on the low voltage side of the coil.
but apparently there would be a lot of distortion and high peaks to deal with.
So i had to come up with something different.

Idea 2
Someone suggested me to take an incoming alternator signal, and indead on that signal there are a lot less strange peaks (logically ..).
so i will use some kind of "cross zero detection" but then i just have to figure out if one period of the sine wave, is also one complete turn of the engine.

Here i have a scope image of One phase of the alternator
Stupid as i am, i forgot to look at the time/devision, but i will measure it again later.

Re: Build of a Honda CB125S

Sounds interesting. I'm guessing the strange peaks are caused by the back EMF created by the collapse of the magnetic field in the ignition coil.

With a 12v ignition system the primary of the coil is at 12v whenever the points are open, and at roughly 0v whenever the points are closed. And there is some HV noise spikes on the transitions. If you clean up the signal it should work.

Re: Build of a Honda CB125S

Is there any reason you don't just wrap a wire 10 or so times around a plug wire and pick up the inductive signal from the spark?

Re: Build of a Honda CB125S

lucaspa said:

Sounds interesting. I'm guessing the strange peaks are caused by the back EMF created by the collapse of the magnetic field in the ignition coil.

With a 12v ignition system the primary of the coil is at 12v whenever the points are open, and at roughly 0v whenever the points are closed. And there is some HV noise spikes on the transitions. If you clean up the signal it should work.

Click to expand...

Waay more than noise on the primary of the coils. The coil and the condenser comprise a high frequency parallel resonant circuit. The resulting signal is more like a ringing sine wave when the points open and the magnetic field collapses. Then when the points close, whatever residual charge is in the condenser is going to show as a spike.




Throw in a few harmonics, and it'll look more like this:

Re: Build of a Honda CB125S

SONIC. said:

Is there any reason you don't just wrap a wire 10 or so times around a plug wire and pick up the inductive signal from the spark?

Click to expand...

Yeah, i know, it would be a lot easer, but i am not doing this because it is easy, i want to have a real accurate rpm gauge, an since i am going to make a voltage meter/protector in it, i tought it would be Best to use a µC and give all the input to that. eventually i wanted to put some kind of anti theft protection in it. if all this is overkill for a classic bike is personal meaning, but at least it is home made ;D.

and indeed on the primary side of the coil, i got those kind of measurements on the scope.
i guess there is enough time between these peaks to use that signal in idle, but at 7000rpm, it is unusable (I think).

Re: Build of a Honda CB125S

Google "tachometer signal converter"