Author Topic: Smoking coil!  (Read 1337 times)

Offline andy120t

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Smoking coil!
« on: June 09, 2021, 04:07:14 PM »
What have I done - I have an idea, but I wonder if I've damaged anything?

I bought a  spare 550 engine which I've seen bench run. Wiring was minimal. I wanted to then test it still home so wired up myself..
- power via a fuse to the coils
- trigger wires from the points to the coils
That's it. Basic wiring. I checked one spark plug using the kick start and it sparked ok, then I forgot to take the fuse (my ignition switch) out.
Faffed about for 10 minutes trying to connect a 'too narrow' fuel pipe to the carbs, then realised there was a funny smell and smoke rising from one coil. Fuse out, fire averted, no fuel anywhere. But the coil was too hot to touch.
 
Most of the wires and connectors are new, clean and cold. Just the coil is hot. I've read up a bit and had a look at the points - one side will take a .2mm feeler but not a .3mm. Other side is closed shut and this one is linked to the hot coil. So is this constantly triggering the spark?

- I assume then that this means something Is permanently occuring in that coil? Is that a permanent high current flow?
- Might the coil be ruined and what / how do I test. Just the resistance levels?
- Can I reset the closed points easily ( just by moving them to get a basic gap?) ..I haven't ever encountered them before, it's like seeing an 8 track!
- Any other thoughts about what could have caused this,mid not the above?
Thanks!
« Last Edit: June 10, 2021, 06:07:30 AM by andy120t »
andy120t

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Offline hairygit

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Re: Smoking coil - help!
« Reply #1 on: June 09, 2021, 04:20:37 PM »
Welcome to motorcycling Stone Age style! If you rotate the engine on the kickstart, the other set of points should open about half an engine rotations time. Yes, the points when they are closed are energising the coil they are connected to, when they open, the coil produces the spark. As regards whether you have damaged the coil, the only was to know is try it! Smoke, to replace that which was escaping from the coil used to be available at Lucas and some auto electrical specialists, but is as rare as camera film these days

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Re: Smoking coil - help!
« Reply #2 on: June 09, 2021, 04:22:50 PM »
"So is this constantly triggering the spark?" No, it's constantly trying to charge the coil ready to spark.

Coil sparks when points open, and from the power you've just stored in them while the points are connecting the earth route.

Let it cool and then try it to see if you get any spark from that one, then go from there if it doesn't work.


Offline andy120t

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Re: Smoking coil!
« Reply #3 on: June 10, 2021, 06:38:19 AM »
Right, so the points are opening and shutting ( that makes sense when you see them working  :) ) but I didn't get a spark from either coil. I've put the battery on charge to be safe so will try again later today and report back in the spark.
In the few minutes I was trying though the same coil was warming up again.
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Re: Smoking coil!
« Reply #4 on: June 10, 2021, 10:19:18 AM »
Disconnect the supply on the hot one for now and then see if the other has anything wrong by trying it.

Recheck all other connection to make sure of integrity first.

Offline Lobo

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Re: Smoking coil!
« Reply #5 on: June 10, 2021, 12:42:51 PM »
I once killed a ‘750 coil by seeking perfection balancing the carbs on a hot summer’s day. Extended idling / 3000RPM, rising heat, no airflow over the coils..... 4 days later one failed. Bugger.
Bad luck or otherwise I don’t know, but now I stick a fan in front of the bike when tuning it.
Hope no damage done Andy.

Offline andy120t

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Re: Smoking coil!
« Reply #6 on: June 10, 2021, 02:44:17 PM »
Thanks all! Ive checked connections and added an ignition switch. Just waiting for battery to charge up ...on a slow charge at the moment.
andy120t

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Offline deltarider

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Re: Smoking coil!
« Reply #7 on: June 10, 2021, 03:46:16 PM »
Andy, maybe I've missed it: do you have a multimeter and have you measured the resistance of the coils primary and secundary circuit? Original TEC coils should have 4-5Ω primary and 13-15kΩ secundary.
Lobo when your coiled failed, did that occur abruptly or was gradually. Have you measured it?
I ask, because I'm still in the process of finding out if a coil that measures OK, nevertheless can be bad.

Offline andy120t

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Re: Smoking coil!
« Reply #8 on: June 11, 2021, 04:30:51 PM »
I have a multimeter. I checked continuity from battery positive all through to the points gap and there is continuity for both circuits. Should there be continuity all the way back yo the earth lead?

Primary  coil- one side shows 3 and the other shows 6.8 ( this is the one that was smoking). I also have a TEK coil from something which shows 3, as do a the two coils on my 650. So does that mean one is spoilt?

Secondary..don't I need to remove plug caps? I'm a bit unsure of doing that in case I break them.. do they just slip back on?

Battery may also be an issue. I had a new one but its only charging up to 8v do it's going back to be swapped.
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Re: Smoking coil!
« Reply #9 on: June 12, 2021, 07:43:26 AM »
Battery volts at 8 probably won't give you spark at all,  so check again the good coil when you get another.

Looking like that 6.8 tested coil may be unserviceable, either through leaving it on or possibly it was failed before.  Just test your system with new battery with the positive feed for that one apart. Then briefly try it if the other checks out,  but hope for that one diminishes.

Test of HT circuit, yes you need plug leads to have caps removed,  if NGK type they just unscrew to remove and refit.

Offline AshimotoK0

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Re: Smoking coil!
« Reply #10 on: June 12, 2021, 10:43:58 AM »
Make sure your meter is capable of accurately measuring low resistance accurately to 0.1 of an Ohm (usually 100 Ohm range) and also don't forget to short together the two probes and measure any  test lead resistance and subtract that from your readings. On some meters, like my expensive Fluke model, you can 'null' out the cable resistance. Post a pic of the one you are using for more help.
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Offline andy120t

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Re: Smoking coil!
« Reply #11 on: June 15, 2021, 01:22:50 PM »
New battery with a full charge made all the difference. I have a good spark in the coil that wasn't smoking and nothing from the one that was. I've swapped the wiring over and the 'good' coil still gives a spark, so my wiring is OK.

I've also plugged in another coil from elsewhere and this gives a spark where the smoking coil didn't, so I'm sure that the smoking coil is scrap. Pity really, as the engine was running on all 4 cylinders, but I feel I've learnt a bit about wiring the points ignition and how they work - and importantly, what can go wrong in the absence of an 'engine run' switch which I will now be adding in.

One clarification/ question - when the points are closed, is the current just earthing through the points backplate?

Also a piccie of the coils on this engine - they look a bit precarious, is there anything I can use to hold them on .. electrical tape? Would a jubilee clip to and too metallic? All my other coils are screw-in ones and the wires look fairly secure. [ Guests cannot view attachments ]
« Last Edit: June 15, 2021, 01:52:04 PM by andy120t »
andy120t

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GSXR 7/11 - I need to sell it
Triumph 5TA - and this..

Offline andy120t

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Re: Smoking coil!
« Reply #12 on: June 15, 2021, 01:37:58 PM »
Ash - Piccie of my multimeter..

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I think I'm getting the correct reading with that setting, but please let me know if not!
thanks

« Last Edit: June 15, 2021, 01:40:22 PM by andy120t »
andy120t

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Re: Smoking coil!
« Reply #13 on: June 16, 2021, 10:39:32 AM »
"One clarification/ question - when the points are closed, is the current just earthing through the points backplate"

Yes, the primary circuit is completed by earthing through that route. With the points closed the primary coil winding induces energy to be stored in the secondary "HT" windings that are wrapped around the primary, but not connected to them. In concept like the current contactless charging systems for phones etc.

When the secondary coil holds enough energy,  the primary earth is opened with the points. At this point the energy wants to escape from it's stored state and lacking that primary route will seek any earth, which is supplied by the leads and spark plugs ultimately to give a ground route out, jumping that plug gap then gives us the spark.

There's a system backlash too, just as the plug starts to spark it comes back through the entire system to induce an escape route across the points gap but prevented from doing so by providing a buffer in the form of the condenser to absorb the shock sufficient that it's unwilling to jump the points gap. If the condenser fails, then the spark jumps the points gap and doing so terminates the one at the plug.

It's really a little bit of a magical balancing act reliant on helpful potential faults and useful characteristics being arranged in balance over the whole system.

Offline McCabe-Thiele (Ted)

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Re: Smoking coil!
« Reply #14 on: June 16, 2021, 12:00:09 PM »
"One clarification/ question - when the points are closed, is the current just earthing through the points backplate"

Yes, the primary circuit is completed by earthing through that route. With the points closed the primary coil winding induces energy to be stored in the secondary "HT" windings that are wrapped around the primary, but not connected to them. In concept like the current contactless charging systems for phones etc.

When the secondary coil holds enough energy,  the primary earth is opened with the points. At this point the energy wants to escape from it's stored state and lacking that primary route will seek any earth, which is supplied by the leads and spark plugs ultimately to give a ground route out, jumping that plug gap then gives us the spark.

There's a system backlash too, just as the plug starts to spark it comes back through the entire system to induce an escape route across the points gap but prevented from doing so by providing a buffer in the form of the condenser to absorb the shock sufficient that it's unwilling to jump the points gap. If the condenser fails, then the spark jumps the points gap and doing so terminates the one at the plug.

It's really a little bit of a magical balancing act reliant on helpful potential faults and useful characteristics being arranged in balance over the whole system.

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