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Points problems, 1976 Honda CG 125

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CarlB
L Plate Warrior



Joined: 20 Aug 2018
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PostPosted: 20:13 - 20 Aug 2018    Post subject: Points problems, 1976 Honda CG 125 Reply with quote

Hi, new to the forum, just thought I'd post this in case it helps anyone else.
Gradual points creep on an old bike.
I bought a '76 cg125 a few weeks ago for a trip to France; it was mostly in good condition with a little bit of obvious work to do. The stator coil for the battery was shot so I had them both rewound, I fitted a new battery, I checked all the wiring and replaced connectors and sealed everything against water, I put a new back mudguard on to take the weight of a back rack as the old one was badly rusted and I cleaned and adjusted the back brake and replaced the front brake cable. The points were a shiny, newish replacement and worked fine. Remember that!
A few test runs and it all seemed good to go.
Once in France, in very hot weather, I found the bike beginning to falter.
First symptom: it died when coming to idle after a long run, I checked the plug, which was sooty, so then the air filter, fuel flow, dismantled the carb, nothing obviously wrong there so I suspected the timing. Off with the gear lever, side cover, checked the points gap- no gap. The retaining screw was still tight so that's odd. Adjusted the gap, let the bike cool down and rode on. Second time it happened, the next day, it faltered after a couple of hours riding and smoked a bit too, excess fuel smoke. Symptom of retarded timing, amongst other things. I wondered if the advance/retard springs were too old, maybe getting hot and weak and not pulling the rotating cam back to the low revs position properly; so off with the stator cover, the springs seemed fine, put a little oil on their pegs, adjusted the points gap again, let the bike cool and rode on. Over the next couple of weeks it became a daily routine to stop when the bike began to falter and smoke, take the cover off, adjust the points and ride on. I convinced myself that the heat and vibration was causing the points to creep very slightly and gradually retard the timing and the adjustment is so minute that it's really impossible to see any obvious difference in the screw position.
Ok, so today, still in France, it happened again but this time there was no more adjustment on the points. The slot on the backplate was at the max for advance so after today's adjustment there would be no more. Finally I realised that the cam follower must be rapidly wearing out, which was weird, until I inspected the cam closely and saw a little patch of pitting, old corrosion, which was acting as an abrasive, wearing down the soft cam follower pad.
Little hope of finding new points here in a day so I had to bodge. Chemical metal putty to rebuild the cam follower by a mil or so, and a tiny strip of brass foraged off my 6v testing screwdriver as a face to resist wear on the steel cam.
So far, it works. The bike runs ok. I've done a couple of short runs but I want the chemical metal to harden overnight before I stress it any more. The next long run will either be trouble free or I'll have bits of brass and resin flying off into my stator!
What I've learned so far: don't get fixed on a diagnosis, there might be another cause behind the problem that I haven't seen yet.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 21:46 - 20 Aug 2018    Post subject: Reply with quote

Interesting fix.

Oddly, I'm struggling to find a seperate points cam listed anywhere for an early CG125, even on the parts fiches. Is it actually a seperate part or is it part of the crank itself?

Is the felt pad stil in place and lightly oiled?
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bikenut
World Chat Champion



Joined: 21 Nov 2011
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PostPosted: 10:33 - 22 Aug 2018    Post subject: dwell Reply with quote

Mostly, but not always, the cb points cam is part of the flywheel hub.

Some will have a centrifugal ign advance mech as well.

Well done for getting the flywheel off without wrecking anything, and note be very careful when refitting else bend the points arm !!

Find the sweet spot or max " points gap" when refitting the flywheel, then un adjust to correct gap.
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steve the grease
Crazy Courier



Joined: 26 Jan 2018
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PostPosted: 19:07 - 23 Aug 2018    Post subject: Reply with quote

These old flywheel magnetos are very familiar to those of us old enough to remember Villiers engined bikes etc. The cam is part of the flywheel, if you look the outside of the boss with the taper hole in the centre, you will see it's not round, but made so the points are held open for most of the rotation , closing about a 1/4 turn before they re-open at 'F'. If the cam surface is rough ( like it might be on an old bike thats been parked up for ages) it will wear away the heel of the cam quite quickly - result no points gap and no spark. If you get some very fine ' sand paper' emery or one of those green scrubber pads with a bit of oil and rub till the steel is shiny ( or certainly remove any roughness) and you should be OK. A light smear of grease, (not loads) reset the points if the heel is not too worn and away you go.............
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bikenut
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Joined: 21 Nov 2011
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PostPosted: 11:08 - 24 Aug 2018    Post subject: Reply with quote

:D villiers, there's modern for you.....some self extracting and some self keeping...........interestingly and by the by, some outboard motors have a separate points cam........
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CarlB
L Plate Warrior



Joined: 20 Aug 2018
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PostPosted: 20:15 - 08 Sep 2018    Post subject: Points problems, 1976 Honda Cg125 Reply with quote

Update: the bike made it back from France with no more problems and I've replaced the points. The points cam is a separate part, held to the inside of the flywheel by two screws and tabs, but I haven't been able to find a clean replacement yet. The pitting is deep enough that I'm worried about reducing the cam depth too much if I polish it out. A ew one is the best fix. The oil pad for the cam is there and I oiled it in France but it may not be new enough to maintain constant contact. Much as I like the bike, I decided I need a bit more HP for longer trips and hills so I've just sold her to a local young enthusiast and I've shown him the cam and explained how to adjust the points etc. I'm still looking for a replacement '76/'77/'78 cam for him if anyone know of one...?[/img]
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Triton Thrasher
Could Be A Chat Bot



Joined: 16 Oct 2012
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PostPosted: 20:30 - 08 Sep 2018    Post subject: Reply with quote

Modern replacement points are notoriously not as good as original.

There is special points heel grease available. Don’t ask me where: I gave up and fitted electronic ignition on my old bike.
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