Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: oldtuggie on April 02, 2022, 02:40:29 AM
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1976 550 four f1 supersport
Hi can anyone advise me how to use a multimeter to test a suspected faulty ignition coils
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Disconnect the coils then do a resistance(ohms) test between the two small leads and again between the two ht leads with plug caps off, also test the plug caps seperately.
Coils rarely fail but plugcaps do
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Like Bryan said, all suspect the coils, but usually they are OK. Let's take the stock configuration, meaning OEM coils and resistor plugcaps. The coil has two circuits: the primary and the secundary. The primary should read between 4 and 5Ω, so you select the 200Ω range for this. The secundary circuit of the coil itself, with plugcaps removed, should be between 14 and 15kΩ. To measure an individual, disconnected plugcap, select the 20kΩ scale. Each plugcap should read 5-8kΩ. If you read zero, that cap is not the resistor type and then it makes sense to have resistor plugs because you need some resistance in the secundary circuit. It should be resistor plugs or resistor caps, not both. So in total the secundary circuit will be between 24 and 31kΩ. BTW, for that you need the 200kΩ scale. You could start to measure the secundary circuit in total by just pulling the caps from the plugs and then have one probe in cap #2 and the other in cap #3 and for the other in cap#1 and cap#4. As said the secundary resistance inside the coil itself usually is 14 - 15 kΩ. An individual cap's resistance should not be over 8 kΩ. So with the plugcaps connected to their wires, total resistance should not be over (15 + 8 + 8 = 31 kΩ. If it is, plugcaps should be unscrewed from their wires for individual measuring. I'm not fond of R type plugs. Their resistance tend to increase faster than the resistor caps in my experience. You can measure the R plugs resistance by putting one probe to where normally the cap sits and the other probe to the center electrode (a bit difficult but it can be done). When over 8 kΩ, replace.
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Nice one Deltarider, just what I needed too.
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HONDA IGNITION COIL REPAIRING WITH NEW HT LEADS
https://www.dropbox.com/s/x0a4fcpmrwm3l19/Ignition%20coil%20fix.doc?dl=0
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:) :) Nice one Ash too, as I didn’t throw my old coils away and had a DeWalt multi too for Christmas!!
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Gonna have a go at this so that saves me looking for it again, cheers Ash. My leads are so knackered they just hang limp on one of the coils, thought I might have a go after reading ot a few months back. :)
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Thanks for the replies guys, brilliant advice.
2&3 cylinders had stopped firing swapped condensers but it made no difference swapped leads on coils and plugs an 2&3 fired immediately, I assumed it was the coil never thought of the lead or cap.
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Hi just a question about the primary resistance. I’ve just tested the 2 old coils I had, and 2 new ones now fitted, and on all 4, using 2 different multimeters, the primary ohm reading is zero.
The advice says 4-5 ohms?, I can’t believe the zero readings could be ‘wrong’ on all 4. Any thoughts very much appreciated.
I’ve be doing all the usual checks due to occasionally stalling when hot, and I’m currently also checking for induction air leaks.
(I changed the coils because the leads were poor, and possibly a dud cap was the main issue)
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Your meter is on the wrong scale or duff
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Strange, both meters show the right ohms for the secondary side.
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The coil has two circuits: the primary and the secundary. The primary should read between 4 and 5Ω, so you select the 200Ω range for this. The secundary circuit of the coil itself, with plugcaps removed, should be between 14 and 15kΩ. To measure [...] select the 20kΩ scale. Which means: after measuring the secundary circuit, you'll need to select the 200Ω range for the primary. Did you?
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Many thanks. I tested a spare resistor plug DR7ES and got around 5 ohms using the 200 ohm scale.
Doing the same on the 2 small coil input leads get zero on each of 4 coils. Very odd.
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I tested a spare resistor plug DR7ES and got around 5 ohms using the 200 ohm scale.
Doing the same on the 2 small coil input leads get zero on each of 4 coils. Very odd.
Very odd indeed, a DR7ES should read 5kΩ. In the 200Ω range it should produce a I, indicating the resistance is beyond the selected scale.
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Sorry I misread your instructions. All clear now. I was confusing the 200 with the 200k
🙄
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Having rechecked everything on the new DSS coils, the primaries are showing 3.4 ohms and the secondaries with new 5k ohm NGK caps are totalling 21.5k ohms (not far off your 24!) Would those levels cause particular symptoms?
The bike runs well apart from the occasional hot tickover stalling I’m investigating.
Many thanks again, having learnt a lot.
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Having rechecked everything on the new DSS coils, the primaries are showing 3.4 ohms and the secondaries with new 5k ohm NGK caps are totalling 21.5k ohms (not far off your 24!)
When measuring low resistances, in the 200Ω range, it's good practice, before you start measuring, to firmly hold the probes to each other, to read the internal resistance (see pic below). Usually it's around 0,3-0,4Ω, which means the actual measuring will result in a reading that will indicate a 0,3-0,4Ω higher resistance than it actual is.
Would those levels cause particular symptoms?
Mwah. The primary resistance is on the low side, which could cause extra pitting at the breaker points, as they switch a higher current. Standard is 4,3 - 4,7Ω. Was DSS open about they're being not standard? Could you post a link to them?
The bike runs well apart from the occasional hot tickover stalling I’m investigating.
Owners of a CB500/550 should be aware of a typical weak point: the plugcaps. They're weak in two aspects.
1. They're exposed to rain and wind which effects their reliability. As a matter of fact, in the 42 years I own my bike there's been only one occasion, I didn't make it home. In torrential rain, they and/or the HT leads got soaked and the engine died.
2. GND (ground) is often all too close to the HT leads and/or caps. Checking is simple. Have the engine run in the dark and watch closely if you see arching between the plugcap and/or HT lead to the head. When concentrated, you can even hear it spark, which means that the spark you've witnessed, has not been delivered in the combustion chamber.
Another simple test is to check the condensers are not leaking. Faulty condensers may cause arcing as shown in the vid: https://www.youtube.com/watch?v=t3cuvGVwnjI At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner
Whilst you are there, also see to it the forked connectors at the back of the breakerpoints are not accidentely grounding to the plate. This can be intermittent! Especially the 2+3 breakerpoint has its connectors dangerously close to the crosshead nearby.
BTW, are you familiar with Ohm's law? I have a very simple and practical formula related to your bike, which will make it clear and impossible to forget.
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Static measurements are on thing, but operation under load is another. In other words although the ohmic resistance measurements indicate healthy conductivity and windings, it’s not a good indicator of conductor insulation quality as this breaks down with age and use leading to leakage/tracking and ultimately a weakened or complete loss of spark. I’m pretty sure Ash built a test machine to test the coil functionality at both frequency and voltage?
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Actually some time ago I'va asked Ash if I could build a simple one myself. Might be to complicated, though.
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Many many thanks both for your time. Condensers are good. I will monitor over time and check the points for degradation. Some great learning points, one of the pleasures of ownership and restoration.
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Could you post a link where DSS advertises the coils you have?
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Sure this is it:
https://www.davidsilverspares.co.uk/CB500K1-FOUR-1972/part_83526/
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Thanks. I believe it's the same product CMSNL offers: https://www.cmsnl.com/honda-cb500k1-four-england_model14660/coil-rlignition_30501300003p/
A few comments if you allow me. It's a generic product. Colours and gender of the primary leads is 50% incorrect. Both NEG wires are yellow. One should ofcourse be blue, but that's a detail I could live with. The connectors at the NEG wires are male, but should be female. Crimping connectors is an art in itself. Don't ask me how I know. ;) On the plus side, I would not mind the spade connectors yours has at the coils.
More important however: the resistance of the primary circuit should be in the advertisement. When not in the advertisement, it should at least be on the package it is in, so you could return it unopened. Some retailers will not accept returns of electric equipment once opened. When neither is there, for me enough ground to return them. It would be merely out of solidarity with other customers. They should not have to guess. I have no less than four multimeters, one upstairs, one in the garage and two onboard my yacht. Failing to publish the primary resistance, could be for a different reason: the manufacturer cannot guarantee a precision within a band of let's say 0,5Ω. Manufacturer is most likely located in China.
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Many thanks again.