Ignition coils

[Sesman]

What are the chances of both ht secondaries simultaneously going open circuit. Primaries are might fine showing continuity and 4 ohms.

I’ve tried continuity between ht leads both with caps and plugs installed and bare, exposed innards. iv’e also tied the plugs together and flashed the live/contact beaker wires to a battery to generate a spark…. I get nowt.

Is this a common occurrence or am I missing something?

Any contributions gratefully received.

[SteveD CB500K0]

If this is 1/4 or 2/3, then the HT leads are just the two ends of a single winding.

So not an unexpected result.

If it’s 1/3 or 2/4 then I would expect the universe to end before both broke at the same instant (other than though catastrophic impact damage…)


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[AshimotoK0]

What resistance range are you on.. you are measuring typically 15,000 Ohms so you need to be on the high resistance range. that's the bare ends with no resistive caps , which would add typically another 5,000 Ohms  for each cap. You also  need a capacitor (condenser) in your test circuit to build up the energy to produce a full spark

[Sesman]

Ahh, capacitance.

But should I not have continuity between the plugs/leads?

[AshimotoK0]

Ahh, capacitance.

But should I not have continuity between the plugs/leads?

Depends what you mean by continuity .. yes there should be resistance between the two HT leads but you will need to measure on typically the 100k Ohm range . On lowere ranges the resistance may not rregister and appear to have no continuity. It's very rare for secondary coils  to go open circuit BUT very common for HT leads to fatigue where they exit the coil body hence giving an open circuit reading. Hope this helps.

[Sesman]

Thanks Ash. To be honest I’m absolutely no sparky in any sense. I just presumed that doing a continuity test (not an ohmic measurement) would give me an initial indication of general functionality. I’ve used a martindale across the secondary and get no response. Could the relative internal impedance of coil versus instrument be the problem?

Is there a better way to test? Not sure why I need a condenser in circuit to generate a spark as I’m simply flashing the primary across 12v…I’m totally flummoxed.

[Sesman]

I’ll Jerry rig the coils in situ and crank the engine….fingers crossed?

[heli_madken]

Happened to me in 1979 on a GL1000, engine cut dead. For the life of me to this day I cant imagine how it could happen to both coils at the same time. Dad towed me home which of course would never be allowed now. Local Honda dealer only had CB400 coils in stock and as I needed the bike for work I had to jury rig the and make do, went on that way for the next two years before I bought new coils.

[AshimotoK0]

"Without the capacitor, the points will be rapidly eroded  and the collapsing magnetic field will expend a good part of its energy as a few dozen volts maintaining the unwanted arc across the points".
Trust me .. without a capacitor you will get s very weak spark or not at all from the secondary of the coil

[Sesman]

I trust you fully Ash. I totally get the stored energy concept to minimise sparking across the points. Could it be that the volt drop across the 15kohm secondary is so high that it can’t drive the buzzer in the continuity testing device?

Would you know what type of meter is being used in the workshop extract attached?

I’ll connect the coils up and test in situ by cranking the motor after testing the primaries and points circuit in situ, that should eliminate all but the secondary coils. If I do need replacements, can you recommend a product?

Thanks for your help with this.

[Sesman]

Possibly sorted. The volt drop across the plug cap and plug is so high as to mute the buzzer. Me thinks a more appropriate instrument is required. I’ll resort to my pragmatic approach as outlined in the earlier post.