NEWS FLASH - December 2013
We are now selling magneto bearings, insulators, oil seals and armature shims from our on-line shop.

Brightspark Magnetos

NEW ... Take a look at some of the equipment we use in our workshop for magneto servicing and overhauls.

 

 

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DIY Magneto Maintenance and Troubleshooting

Bearings and Bearing Insulators
Pick-up, HT Lead and Plug-cap - 1
Slip-ring
Contact-breaker Assembly
Cam
Internal HT Continuity
Main-body Earth Brushes and Bearing Insulators
Contact-breaker Re-installation and Points Setting
Low-tension Continuity
Earth Brush Continuity
Complete High-tension Continuity
Will It Spark?
Timing
Pick-up, HT Lead and Plug-cap - 2

 

Contact-breaker Assembly

Having removed the contact-breaker assembly from the magneto, disassemble it, noting where each part was.

 

Check the state of the points surfaces. If necessary, dress the points on a fine stone. The points surfaces should be very slightly convex, so don't worry about getting them perfectly flat. However, don't make them lop-sided. Even if the points surfaces look good, clean them with fine emery cloth to remove any oxide layer. Then wash the points with petrol and dry them.

 
  • Ring cam versions:

    • Check the state of the contact return spring and replace if broken.

    • Clean and grease the moving-point pivot. If not free to move, ease it. If sloppy, consider fitting a new moving point (Lucas), bush (BTH), or pivot post.

    • Check the state of the heel of the moving-point assembly. If excessively worn, replace the heel (BTH), or the moving-point assembly (Lucas).

    • If an earth brush is fitted behind the back-plate, check that the spring is good, that the brush is free to move and that it is not unduly worn in length or diameter.

 
  • Face cam versions:

    • Check the state of the tappet and replace if necessary. Put a smear of grease on the tappet shaft.

    • Check that the felt pad in the end of the screw holding together the two blocks of the points assembly is present and good, and soak it in oil.

 

If the magneto is fitted with, or about to be fitted with, a Brightspark EasyCap, you can perform some basic checks on the EasyCap.

 

With your multimeter set to display resistance and connected to the opposite faces of the circuit board of the EasyCap (and with your fingers touching no more than one side of the circuit), the meter reading should climb up from a low value until it goes off the scale (OL). If you have an auto-ranging meter, the reading might jump about a bit on the way while it changes scales.

 

If your multimeter can measure capacitance, the reading should be within 10% of:

  • 150 nF (0.15 uF) for the C01, C02, C03, C05 and CU/150 EasyCaps;

  • 136 nF (0.136 uF) for the C04 EasyCap;

  • 220 nF (0.22 uF) for the C06, C07 and CU/220 EasyCaps.

 

If you have a Megger or similar insulation tester, set it to test at 500V. The resistance between the two sides of the circuit board (with your fingers well clear) should climb to in excess of 2 GΩ (2000 MΩ).

 

If your magneto does not have an EasyCap but it fitted with a condenser buried in the armature, then it is impossible to check the condition of the condenser, while the armature is assembled, without specialised equipment.

 

Check that all the insulators are in good shape, and reassemble the contact breaker assembly.

 

With the contact-breaker assembly still removed from the magneto, and with a multimeter set to measure resistance, check that with the points closed there is a short circuit between them (as close to 0 Ω as your multimeter goes). Also, with the points open, check that there is an open circuit between them; if fitted with a Brightspark EasyCap, it will take a little while for the resistance reading to climb off the scale.

 

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