Hi first may i apologise if this has been discussed before ,but can anyone tell me how to test if a coils dead with a multimeter please.
Cheers Steve
Testing coils
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Ian Malcolm
- Posts: 108
- Joined: Thu Mar 30, 2006 11:42 am
- Location: London, ENGLAND
Basically, you cant 
BUT you can tell if its sick.
A single shorted turn on the HT winding wont show up on a multimeter. but will either totally kill the spark or result in one thats so feeble that it cant jump a normally gapped plug under compression.
HOWEVER, you *can* check for open circuits (broken wire) in the HT winding. If there is a small break in the winding, the coil will often work normally at first or while cold, the spark jumping both the plug gap and the break, but over time the spark at the break erodes the insulation of ajacent turns eventually leading to a short and a dead coil. (which may show up at first when hot - a bad coil can do a lot of odd things and really drive you nuts)
You just disconnect the *whole* HT lead, and measure from the little pip in thebottom of the HT connector on the coil to the flywheel baseplate with the meter on a resistance range. If you find the correct resistance there (say +/- 10%), the coil is probably good. If it reads way low, there is almost certainly a serious short and I would suspect the coil has seen rather more salt water than was good for it and if it reads high or open thats a coil on the way out, even if it isn't actually dead yet (dont trust it to get you home . . .)
The HT lead shoud be solid copper cored and may have a resistive surpressor lump somewhere along it (old ones, not very trustworthy now and due for replacement or rebuilding with new wire). If it has a resistive surpressor or an aftermarket resistive plug cap, the resistance should be marked on that part and thats what it should measure end to end, otherwise not more than an ohm or two. (series resistances add) I include this in case you are boat jumbling and are trying to check a coil from the plug cap to base plate because you dont want to piss off the seller by dismantling everything
I can only help with the coil HT (secondary) resistance measurement for WIPAC points ignition, I dont have the readings for the WIPAC electronic ignition or the old Villiers coils, perhaps one of the 'gurus' can help with the others.
WIPAC points (gold/copper paint flywheel) 4K - 5K
(All I've seen have measured 4.3 - 4.7 Kohm)
BUT you can tell if its sick.A single shorted turn on the HT winding wont show up on a multimeter. but will either totally kill the spark or result in one thats so feeble that it cant jump a normally gapped plug under compression.
HOWEVER, you *can* check for open circuits (broken wire) in the HT winding. If there is a small break in the winding, the coil will often work normally at first or while cold, the spark jumping both the plug gap and the break, but over time the spark at the break erodes the insulation of ajacent turns eventually leading to a short and a dead coil. (which may show up at first when hot - a bad coil can do a lot of odd things and really drive you nuts)
You just disconnect the *whole* HT lead, and measure from the little pip in thebottom of the HT connector on the coil to the flywheel baseplate with the meter on a resistance range. If you find the correct resistance there (say +/- 10%), the coil is probably good. If it reads way low, there is almost certainly a serious short and I would suspect the coil has seen rather more salt water than was good for it and if it reads high or open thats a coil on the way out, even if it isn't actually dead yet (dont trust it to get you home . . .)
The HT lead shoud be solid copper cored and may have a resistive surpressor lump somewhere along it (old ones, not very trustworthy now and due for replacement or rebuilding with new wire). If it has a resistive surpressor or an aftermarket resistive plug cap, the resistance should be marked on that part and thats what it should measure end to end, otherwise not more than an ohm or two. (series resistances add) I include this in case you are boat jumbling and are trying to check a coil from the plug cap to base plate because you dont want to piss off the seller by dismantling everything
I can only help with the coil HT (secondary) resistance measurement for WIPAC points ignition, I dont have the readings for the WIPAC electronic ignition or the old Villiers coils, perhaps one of the 'gurus' can help with the others.
WIPAC points (gold/copper paint flywheel) 4K - 5K
(All I've seen have measured 4.3 - 4.7 Kohm)
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Charles UK
Magneto testing
I have always understood that any form of resister in the HT area is a No No.
The plug cap should have no resistor or supression feature & the spark plug lead solid copper strand.
All these rules apply from the Marstons & all the way through the Seagull product range right up to the 5R.
The plug cap should have no resistor or supression feature & the spark plug lead solid copper strand.
All these rules apply from the Marstons & all the way through the Seagull product range right up to the 5R.
Hello Steve, Have a look at the FAQ page, the methods are outlined there.
There should be no resistance in the HT lead, if there is I bet there is corrosion. The old leads with supressors should be treated with grave suspicion,as they are at least 25 years old.
Seagull used to recommend changing HT lead and cap, plus plug, every year, cerainly every 5 years is a good idea.
HT leads and caps are only £11.75, plugs £4/50. all on the shelf here.
Regards,
John
SOS
There should be no resistance in the HT lead, if there is I bet there is corrosion. The old leads with supressors should be treated with grave suspicion,as they are at least 25 years old.
Seagull used to recommend changing HT lead and cap, plus plug, every year, cerainly every 5 years is a good idea.
HT leads and caps are only £11.75, plugs £4/50. all on the shelf here.
Regards,
John
SOS