The
Commando Ignition system mainly uses the following parts. For
Specifications Please go to the Technical
Section.
|
I am going to attempt a basic description of how the Commando ignition system works. I will describe the original system here. Most people including myself prefer aftermarket electronic ignition, such as Boyer Bransden, which is more reliable. For information on Boyer ignition go here. For more detailed information about the specific part either scroll down or select in the above index. The Commando ignition system is relatively simple and comparable to other pre-electronic ignition vehicles. The idea is to obtain a spark at the spark plug in the combustion chamber, when the piston is at 28 degrees ('fully advanced' for details click here) before top dead center on its compression stroke. Each cylinder has its own contact breaker which is mounted on a plate at the right hand side of the camshaft. The contact breakers (points) are opened momentarily by a small camshaft which is screwed onto the end of the main camshaft on a taper. When the points are closed they have 12V from the battery passing through them and when opened a break in current occurs. Mounted below the fuel tank each cylinder/spark plug has its own 6 Volt ignition coil. Each coil has a low tension (Small) wire which goes to the points. The secondary winding coming out of the coil is the spark plug wire which is the high tension side of the coil. When the points open a sudden cut off in current flow in the low tension winding induces high voltage which is sent down the spark plug wire to the plug gap where it sparks and ignites the fuel air mix. If you own a Commando and have not already done so I advise you to get a workshop manual!
|
Ignition Coil (Lucas 17M6 0r 17M12) |
|
All Commando's with the exception of a few in the early seventies were fitted with 6 Volt coils. The coils have 2 windings, primary and secondary. The primary being the input or low voltage and secondary being high voltage. The primary has about 350 windings and secondary about 2000 windings of fine wire. The windings are separated by paper and immersed in oil. Ignition coils require no maintenance, just check terminals! It is possible to do some basic tests on your ignition coil in case you suspect its faulty. To check the primary windings, connect an Ohm meter across the primary terminals. The reading should be between 1.7 and 1.9 Ohms for a 6Volt coil and 3.3 and 3.8 Ohms on a 12 Volt coil. There should be no continuity between the terminals and coil body with the wires disconnected.
|
|
Ballast Resistor |
|
Norton decided to fit 6 Volt coils, as previously described to most Commando's even though they have a 12 Volt system. The reason was because 6 Volt coils give a better spark when the battery is in a discharged condition. This could have potentially happened quite a bit on the later models which had starter motors. The only way 6 Volt coils can be used is with a ballast resistor. When the battery is low the Ballast resistor is by-passed enabling more juice at the coils. The Ballast resistor is mounted near the coils in the ignition assembly below the tank. As with the coils they rarely go wrong. Check terminals and that you have resistance of 1.8-2.0 Ohms across the terminals.
|
|
Contact Breaker assembly |
| 2 different types of contactors were
fitted to Commando's. Pre-1973 had Lucas 6 CA and all 1973 750 and 850's
have Lucas 10 CA. The different types are not interchangeable. Both sets
have their own adjustments with can be independently set for each
cylinder. Without getting into boring details about points I am going to
explain how to adjust them and be done with this part as its basic stuff. Adjustment Remove spark plugs and contact breaker cover. While looking at the cam in the middle of the contact assembly, turn the motor (best put it in 4th gear and rotate rear wheel) until the points are open as far as they go. Its pretty easy to see by looking at the way the points are actuated by the cam. When you have verified they are open as far as they go, check the points gap with feeler gauges and it should be 0.015in.. If its not adjust using the screw so the feeler gauge slides with no play through the gap. Do the same for the other set of points. Both sets of points have to be 180 degrees from each other. My recommendation is to use electronic ignition. The only people who don't use electronic ignition are those who don't understand how reliable it is. They generally believe that it is possible to get out of trouble with points in the event of a failure. In this day and age you must have a cell phone in the event of problem to have your girlfriend come get you. Points do work fine but require checking and adjusting on a regular basis.
|
|
|
|
|