Reply To: Magneto Testing

[sidevalve5]

Hi Andy,

Yes, thats the best way to go and there is no need to get irritated by someone else having a different opinion to yourself. Its part of life and we all have to rub along together.

Out of respect to yourself and George’s experience, also because I wish to gain additional knowledge in this area. I have spent an hour or so researching on the internet of how to test small engine coils. Could only find three methods, a spark test, a resistance test using a multimeter and a test under load using an oscilloscope. With the presumption a spark test under 150lbs sq in is only for the ignition specialists, then the 6mm gap in air with preferably a three probe tester should indicate if the mag is faulty. But without either one or both of the other tests, the only way to repair a mag when relying on a spark test is by firstly careful reassembly and then by parts substitution. This can be time consuming and expensive if there is only a presumption of a fault in a particular part.

A test by an oscilloscope is again really only for ignition specialists. Which leaves us with a multimeter to test with, an instrument highly skilled electronics engineers rely on. The cheapest ones may or may not have questions about their accuracy. Although the reliability of electronic component manufacture and assembly has improved inexorably over the last couple of decades. A more expensive model from a recognized manufacturer should give very accurate results. But for what fellows like us require, believe one under £8 will do the trick. The primary coil and LT circuit resistance test is pretty cut and dried even with a budget multimeter. Secondary HT coils have a huge variation in the expected test results even when new. So slight inaccuracies from a multimeter will not make too much difference. Have watched countless You Tube video’s of professional service engineer’s doing a coil test with a multimeter.

Hope these posts on the forum will help someone in the future to decide which way to go in repairing a mag. Many will undoubtedly agree with you, or do not have the confidence to work on the ignition system and send it off to be tested by an expert. Others may want to have a go themselves. But one thing that has been achieved is the subject has been discussed at length so those that have problems can make an informed decision.

Best wishes,

Grahame