Bernard W317 no spark

[nrbrowning]

Stafor rotavator from 1970s. I can’t get a spark from the ht lead. Any tips or testing routines? Coil and condenser are tested . Contacts too

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[charlie]

First clean and adjust points, they can build up a layer of corrosion. Coil and condenser really need professional test gear to testthem thoroughly, a multimeter will show if condenser is short circuit and if coil, primary and secondary windings, are open circuit. HT lead should be easy to replace if it is suspect. A new plug might help, or at least a known good one.

[sidevalve5]

If you have not done it already, firstly I would remove the points, hone any pitting out from the contact surfaces, refit and set the gap to 0.015”, also clean all terminal connections. With the plug cap removed, hold the end of the HT lead 6mm from a clean part of the engine and see if there is a spark. If there is, you have fixed it, if not, close the gap until its 4mm away. I find holding the HT lead steady difficult, so have got an adjustable spark gap tester that was <£4, its one of the best tools in my box. An engine will start and run with a 4mm gap, but for easier starting and smoother tickover, you really need the gap to be 6mm. A good mag will achieve this. <4mm and the mag needs attention and personally I am not happy until I get it to spark at 6mm. If still there is a poor or no spark, a test with a multimeter is as follows: for LT Continuity, rotate until the contact-breaker points are open. Set the dial to 200Ω, measure the resistance with the two probes shorted together. The reading will probably be a fraction of an ohm and note it. Then measure the resistance between ground and the ‘hot’ side of the contact-breaker. Deduct the noted reading from the reading on the dial and the result should be between 0.5 & 0.7 Ω. A high reading indicates a bad connection or break in the low-tension circuit. A lower reading means there is probably a short-circuit in the contact-breaker assembly or in the armature. For HT Continuity, set the dial to 20KΩ, place the red probe on the pick-up or HT lead, the black to ground, the reading should be between 3 & 7 KΩ. If significantly higher there is probably a break in the HT winding, or a bad connection between the winding and the pick-up. If significantly lower, its unusual, but still indicates a problem. A lot of ignition troubles are due to the condenser. If the LT and HT tests are fine and you have access to a megger, the condenser should pass a 2GΩ @ 500v test. If you cannot do such a test, I would replace it with either a recently manufactured one, not NOS and certainly not second hand. As the wax paper inside them deteriorates with age and use. Or get a modern capacitor such as an EasyCap CU220 from https://brightsparkmagnetos.com/ which is my preference. In my experience they often perform better than old style condensers. Have had instances where a good mag with the existing condenser achieved a spark at 4mm, by fitting a modern capacitor the gap increased to 6mm with the subsequent easier starting and a smoother tickover. Resting a plug on the side of an engine to see if there is a spark is not a good enough test if ignition problems are suspected.

The above is the test procedure for a home mechanic who can use a multimeter. A multimeter will not test the condenser though. Others may advise you go straight to a specialist who may or may not have dedicated equipment. My advice if you are tempted to go down this route is to firstly get a quote, even testing will cost a fair bit. The above is free if you have a multimeter, about £8 – £12 if you have to purchase one. But it will be an investment as it has many uses.

[davidbliss]

Even if you get a spark it maybe not good enough. I have had engines running quite well but if you hadn’t been using them at the time or had in the past you wouldn’t have known something wasn’t quite as it should be, i had a engine suddenly go flat running hot with reduced power, it started just fine and even just altering the mixture helped. Took the coil and condenser in for testing, and condenser was completely shot and wouldn’t even test although engine still started and ran, plugs seldom fail unless the engine isn’t running as it should be and again if there is nothing wrong with a old plug use it.

[andyfrost]

Regarding the testing with a multimeter or a proper purpose built tester , with the purpose built tester you eliminate all the “probablies” or “maybes” , and get a concrete definate answer. It’s down to personal choice , mine based on lifetimes experience(well over 50yrs) is trusting 100% the purpose built tester.

Andy.

[sidevalve5]

‘You pays your money and takes your choice’ with mag testing. A ‘Proper’ test rig would be one that can rotate a magneto, be able to measure the voltage and current output of both the primary and secondary coils. Ideally be able to view the sine waves on an oscilloscope and check the spark gap in air with a 3 probe adjustable tester. For flywheel magnetos, similar except without a magnet passing over the coil, a current is supplied to the primary coil.

Without access to such equipment, only static testing can be carried out by measuring the resistance of the LT and HT circuits. This is carried out with a multimeter.

Condensers can be tested either with a megger or the capacitance function of the high quality multimeter. Have found a lot of ignition problems are caused by the condenser. As I do have a megger, I can test one. For those who do not have access to one, my recommendation if the LT and HT circuits seem OK, is to replace it. But I fit a modern polyester film capacitor with a Voltage Rating of 630v. Capacitance 220nF / 0.22uF. Can get 10off for £4.09p here https://www.ebay.co.uk/itm/301127883221?var=600476142172 I mount them on a small circuit board, but you may get away with a small piece of stiff plastic.

Testing a mag with multimeter is easy, it only takes a few minutes. If I find a fault in the coil, I replace it. If I still do not get a 6mm air gap spark, I replace the condenser with the capacitor above. For me, it’s worked every time. Although I there are some mags with a suboptimal windings on the coil and/or tired magnets. As yet, I have not had one. When I do I will trial again a single wire energy transfer coil system and get the magnets remagnetized.

[andyfrost]

Grahame , firstly I respect your enthusiasm , and ideas. The mag tester I have access to does not rotate the mag , it tests whether the coil/condenser is functioning as it should , obviously if
either fail , they are replaced. After coming away from the test and all is good , then there is simply no need to rotary test. All larger dealers had these back in the day , but with the demise of standard magneto set-ups very few survive today , I would hazard a guess that exteremely few modern day dealers have one , or have even heard of one , I must add that it will not test the modern magnetron type coils.

Andy.

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