Honda CB125 S Ignition points / timing - PROBLEM

[onelitu]

Hi there, I have a Honda CB125 S.
(I am super new to bikes)

I wanted to follow this video :
https://www.youtube.com/watch?v=YxxymqFOdOA
About how to adjust the timing on the bike...
- so that it "should always start the first time! "
Currently the bike doesn't want to start ( the battery is fully re charged and there is a new spark plug(with spark tested).

Unfortunately I quickly realised that on my honda
when the rotar is aligned with the letter F the contact points are almost
completely open?
Here is the video - with photos and footage:
https://www.youtube.com/watch?v=u60wUGzcIuA

How can I fix it?
Thanks for help, your time and any suggestions !
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Honda CB125S

[jaffa90]

The points are secured to a circular back plate which should rotate to adjust the timing by loosening the x head screws/ bolts at 9 o clock and 3 o clock.

[Suntan Sid]

You need to move the backing plate, that the points are mounted on, around, until the correct gap is achieved when the marks are lined up.

I'm guessing, (I'm not familiar with this particular model), but there will be one or two screws, (probably the most chewed up ones), that hold the backing plate in place. Loosening these screws will allow you to move the backing plate around to get the points in the right position.
When I say move around we're only talking a couple of millimetres measured at the outside diameter of the backing plate.

Most importantly, before you do any of that make a mark on the backing plate and the casing, with a marker, so you can move everything back to where it was before you started!
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"Everybody needs money, that's why they call it money!"

[onelitu]

Hi Suntan Sid and jaffa90,
Thanks a lot for the reply.

I added the photo where I understand - I can tweak the plate where the points are locateted ? (similar like on that c90 video?)

The only think I understand from the reference video( of the guy doing similar thing on a c90). You should adjust the plate a little bit more or less 5 degrees ?

In my case its almost half of a turn difference - ( the points should be closed and the roatar should be showing F is that correct ?)
In my case when the rotar shows F the pointa are almost at its maximum open fase ? Can I rotate the points plate by maybe 45 degrees ?

Thanks a lot
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Honda CB125S

[bikenut]

oh what joy.......have very fond memories of a cb125s.....YNT15K are you still alive ??

How long have you had this bike and have you ever heard/seen it running ?

With the alternator rotor set to "F", meaning fire, the points should just be opening.

I cannot remember the points gap but they would be about 12 to 15 thou ish...

The base plate is usually set to the "O" position but some variation may happen........

I would replace the chewed screws.

The rocker caps have been off as well as the head steady bolt by the looks, that's the larger bolt on top of the head.

It does not look as if the cam chain has been looked at as the 2 screws that hold the cam end plate have been touched since new.

You know of cmsnl for the exploded views and have a manual ??

From memory the single mark on the points cam is about the area the points just open.........

You have a transistor radio ??

If you place a transistor radio near your work area, and have the bike switched on, as the points just open you will hear a "click" on the radio. You may even see the points arcing a little bit at the same time.

If you make your self a small test lead with a small bulb you will "see" the points opening.......

You have a strobe light ? a very usefull bit of kit that will do other bikes as well, money well spent. Failing that the red neon plug caps are great for ignition testing of HT as they flash when ht passes thru them, again money well spent. You can actually "see" ht and strength, or lack of ht........

What did you set the valve working clearance to, 2 inlet and 3 thou exhaust from memory.......get the small square "socket" to fit the valve adjust screw tops, again money well spent.

It has spark, has fuel and compression and can "breath" ie no unwanted tenants in the air box etc..........?

The nut that holds the lt ( low tension, 6volts ) from the coil, the insulator system looks a little "crushed" and the points spring is not touching any metal ??

But you do say the bike has ht, a spark........is it happening at the correct time........timing......
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nuts about bikes

[jaffa90]

Q, are the points closed most of the time as bikenut says or open most of the time??
I would remove the spark and detect the piston at the top with the T mark as well.
The valve timing may be wrong causing points timing impossible.
Also is the points cam free to twist and return back ?

[Fizzer Thou]

I also have fond...and some not so fond...memories of my Honda CB125s.Not sure where LMD58K is nowadays but that little bike served me well for 30 months as a commuter while at Navy College.

In my time with that little bike I rode on average 13,000 miles a year as it was my only form of transportation.So when it broke down or needed work I quickly learned how to twirl the spanners.

My first purchase after buying the bike was a Haynes manual,after which a set of feeler gauges and spanners started my tool collection,many of which I still have now,43 years later.

The setting of the points gap was straightforward when following the Haynes manual,so long as no-one else has been in there and upset things by dismantling things like the advance/retard unit,which can easily be reassembled 180 degrees out.

Easy checks like removing the points backplate and ensuring that the camshaft is timed correctly would be a first test.Then when replacing the points backplate,make sure that you align the 'O' to the marker on the cylinder head (unlike that in the video).Make sure that both valves are loose,as if you are going to check the clearances.Then adjust the points gap,nominally to 15' from what I remember.

If the spark at the plug is weak,then several components can cause this ie. a faulty condenser,a plug cap with an open circuit resistive element (looks like a resistor) or a set of points where the heel that rubs against the points cam has worn.I had that problem on a CB550F a number of years later.

With a bike as old as the CB125s then it is best to start by ensuring all of those parts are new.Otherwise you may well go around in circles trying to adjust in one area when the setting you have is ideal.
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Just talk bikes.What else is there?

Always have a 'Plan B'

[bikenut]

Yes, what wonderful little bikes they where, what bsa etc. should have been making rather than the crap tiger cub etc.....

YNT 15K ridden back from cornwall in 1976, screaming down tintern abbey hill the head light main beam decides to blow, i still have dip and the front side light and 150 miles to go, but its was in the summer and light till 10:30 ish......

After chucky chicken on way to welshpool, I thought there was a car behind me at is seemed a bit "Bright", so i glance behind me only to see a largeish trail of sparks!!!!

I looked down at the front exhaust pipe only to see it glowing red hot from the head to the silencer, it was decoking its self !!

I got to my coastal destination before closing time and enjoyed 2 pints.

That bike was brilliant, an unburstable engine, i know cos my younger brother tried to kill it and failed.

I have a slightly older cb125s in the shed which will be tax and mot exempt now.

That one was my lads "training bike". He had a daily commute of about 80 miles to his summer job and loved it.

ps, BE AWARE of the "jesus" clip on the cam chain adjusted foot, it can come off and unadjust the cam chain, see cmsnl for what i mean.
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nuts about bikes

[onelitu]

Thanks all for help - and suggestions.

Hi bikenut,
How long have you had this bike and have you ever heard/seen it running ?
- I have the bike for more than 1 year now, it was full of problems from the beginning. It was running 2 weeks ago. But I always had to push start it - for more or less 15 min, after that it would start. When the engine was hot - than I could use the kickstart - if I wanted to start it again. But when its cold it was always the push start.

- i found somewhere that
CB125 breaker points gap 0.3-0.4mm/0.012-0.016

Both you and Fizzer Thou are mentioning the 'O' for the base plate,
I am attaching a jpg to ask if thats the 0 points?

I would replace the chewed screws.
-Yes, good idea thank you, should I buy this kit to replace those ?
https://www.ebay.co.uk/itm/HONDA-CB-125-S-1972-1980-full-engine-stainless-allen-screw-kit-CB125-CBS-CB125S/122032383445?hash=item1c69b265d5:g:6qoAAOSwCXJbA8Fv

The rocker caps have been off as well as the head steady bolt by the looks, that's the larger bolt on top of the head.
It does not look as if the cam chain has been looked at as the 2 screws that hold the cam end plate have been touched since new.
-Here I am sorry - but I dont understand it...

Hi jaffa90,
Q, are the points closed most of the time as bikenut says or open most of the time??
-Not sure, I will check it and come back to you,
I would remove the spark and detect the piston at the top with the T mark as well.
-How would I do that ?
The valve timing may be wrong causing points timing impossible.
-thats what I think its a problem here... Not sure how to fix it.
Also is the points cam free to twist and return back ?
-Not sure, how can I check this ?

Hi Fizzer Thou,
The setting of the points gap was straightforward when following the Haynes manual,so long as no-one else has been in there and upset things by dismantling things like the advance/retard unit,which can easily be reassembled 180 degrees out.
-how can I check if its reassembled 180 degrees out ?

Easy checks like removing the points backplate and ensuring that the camshaft is timed correctly would be a first test.
- Do you mind explaining here more please ?

Then when replacing the points backplate,make sure that you align the 'O'
-Shall I buy new backplate and points ? again not sure what the 'O' position...

-The park is not weak, the coil and regulator and condenser were replaced.

Thank you very much for help
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Honda CB125S

[bikenut]

Using the picture you posted, the head steady bolt is the bolt at the top of the picture which holds the engines cylinder head to the frame via the brackets, thus acting as a "steady", making the frame stiffer etc..

The marks on the washer suggests that this has been off or loose......a loose engine will vibrate and cause a poor earth !!

A good cb125s will be a good starter, unless it has problems.

Does the carbs choke mechanism work properly and have you looked at the cmsnl exploded views, print them off if you can as they can only help you.

You say the bike now has a good spark ?

Replacement screws may have to be made from screws available from a hardware store, you know how to use a hacksaw and file ?

If making your own base plate clamp screws, remember they will screw into alloy, so the thread ends must be burr free.

Screw down a nut onto the replacement longer screw before cutting it to length, De burr with a file and chamfer the thread end slightly, then remove the nut.

Does the nut pass the thread end all ok by hand ?? If not then its not ready for screwing into the alloy cam cover.

You do not really need a new base plate, just clean up burs etc to make it hassle free.

The screw set is probably for the clutch cover, crankcase and flywheel cover and points cover, the one with 125 cast into it on the cmsnl diagram you have posted.

The alloy rocker cover caps look as if they have been off. I would get some spares of these as even with a really good fitting ring spanner, socket or hex spanner, they can be a real bitch. The seal has a tendance to make them stick and bugger the alloy. Its about applying the right sort of "pressure" to the spanner to remove these, not jerking, to free the stiction of the rubber o ring seal. The oil filter screen uses the same alloy cover.

You know of the centrifugal oil filter on these engines and clucthc cover gasket ? but that's for a little later.

edit test, yep time still this mornings...... :karma:
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nuts about bikes

[jaffa90]

The piston has to be at the top of its stroke and the (T) mark lined up.
The points should just start to open at the (F) mark.
The first video is correct,
When does your points just start to open?
If they just start to open way out then the valve timing and shaft needs checking.
The points cam should be sprung loaded.

[bikenut]

Back for seconds, its quite quiet in the workhouse today.......

Cam timing check.......

ideally the cam cover would need to be removed so you can see the chain, the cam sprocket ( or whats left of it ! ) and the sprockets timing "O" and its corresponding mark on the head.....

This means removing the 2 perfectly "new" screws that hold the cam cover on, as well as removing the ign cam/centrifugal ign advance unit and ideally its drive pin.......but if the spark plug is removed and the engine turned over in the correct direction of rotation ( anticlockwise ) via the flywheel ( should read ALTERNATOR ROTOR ) bolt, look at the valves.

You will see the valve heads and faces open and close.

When the valves are on the rock ( ie, exhaust just closing and inlet just opening ) the timing marks on the rotor should be around the "T" mark, T meaning time or tappets position ( tappets, valve working clearance ) .

Do you have a good fit tool for the rocker arm alloy caps ?

Do you have a good fit screw driver ( JIS type ) for the 2 cam chain cover screws ?

Note.

The centrifugal oil filter ( which you may want to clean out ) lives under the clutch cover, the cover needing a new gasket for refitting.

DO NOT use any sealer for this cover as it has an in built oilway supplying oil to the centrifugal filter and big end.

If this becomes blocked then oil is starved to the big end and filter.

If the filter is "full " ( i have seen them completely full of crap before now so be warned ) then ditto.

The centrifugal oil filter "cap" is held on by 3 small countersunk x head screws which can be problematic, do not ( DO NOT !!! ) use an impact driver to undo these, as a new oil filter cap and body will be needed, so be warned !

The centrifugal oil filter body is held onto the crankshaft via a "slotted nut" ( cant remember if there is a locking tab there as well, but just see cmsnl for checking ) which will require a "peg spanner" to undo it.

It may have been removed before by the last owners using a hammer and chiesel and be butchered.

If so, remove as best as possible and get a new one, the pattern for the tool that you could make ( i made mine way way way back in the 1970'S and still have it, i made several for the different sizes and the cb750 bearing ring for the front wheel, for example ) or buy one from wemoto or similar.

Apart from the alternator rotor extractor tool and a dedicated valve spring compressor ( needed to clear the alloy rocker cap head threads ) , these are the only special tools needed for this engine.

If you need to work on the clutch its self, the centrifugal oil filter parts need to be removed.

Back to ign timing, as fizzer says, check the centrifugal advance unit as they wear, the springs and spring holes.

The points cam must be able to rotate about its "base unit" which is keyed to the cam shaft via the small drive pin. It is sprung loaded via the "fly weights" and springs and return to the un advanced position.

Does the points cam rotate a few degree and spring return ok without the cam shaft rotating ?
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nuts about bikes

[bikenut]

I have just watched the second video you posted.......

the points cam has several marks, one single mark is about where the points just open, and the 2 line mark where they are fully open.

You are aware that the points cam is keyed to the camshaft via a small drive pin, and, the alternator rotor is keyed to the crankshaft ?

cmsnl will clarify.......

the cam shaft needs to be timed to the crank shaft......the engine has compression and turns over all ok ??

Its been ages since i have worked on one of these, rotor numbers ?? cb100s ??

i see you have fitted a new carb ?

you are aware of such stuff as float height ?

you have a manual ?

oh the joys of editing retrospectively.
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nuts about bikes

[onelitu]

Hi bikenut,

Thanks for all the help!

I did some new tests on the bike yesterday - after 15-20 min of running and trying to push started - it fired up. The problem is the same it doesnt want to start cold...

Please take a look on the new video I did:
https://youtu.be/EdEFe-uNdos

the cam shaft needs to be timed to the crank shaft......the engine has compression and turns over all ok ??
- thats the problem i think, you can see in the new video, I think that the cam belt is off by 1 spin? during the test with multimeter the points are just opennning around the F mark, but not on a compression ? How can i fix it, so that the timing of the points are on compression ? (how it should be normally right ?)

i see you have fitted a new carb ?
-yes, new carb that was running rich, thats why I added pod air filter,
once its running its ok, (see/hear the video)

Thank you !
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Honda CB125S

[Suntan Sid]