There are several common faults with magnetos
- Service exchange is available for almost all types of dynamo, magneto or magdyno, or alternatively a large stock is available for outright sale (BTH and Lucas competition models please enquire). Manual advance and retard conversions to your own magneto are also usually available for BTH and Lucas. Please contact us for more details.
- Lucas magnetos and dynamos where fitted to almost all British motorcycles from BSA, Triumph, AJS, Matchless and Norton up to the mid 1960's. If your motorcycle does not have an alternator, chances are it was equipped with a dynamo and also magneto.
The Capacitor
Capacitors, which are short-term storage devices, often fail in older magnetos due to dielectric degradation (short circuit) or conductor breakage (open circuit).
Stuart can sell you a magneto too. Typically, prices for an ordinary road-going mag for, say, a British single will cost around a couple of hundred quid. That's for a completely overhauled magneto with a two-year guarantee on the windings. For a racing mag, you're looking at around £350. These prices are accurate as of May 2011. Magneto tips.
A short circuit absorbs all the power, hence no output or spark. With an open circuit the device has no CAPACITY to absorb the reaction voltage (back EMF) from the coil, therefore this energy is dissipated across the timing contact which quickly burns away. These faults do not necessarily occur instantaneously, they may develop over time leading to a gradual deterioration of the spark output.
Coil Failure
The voltage generated across magneto coils is quite high, in the order of 20,000 volt if no spark plugs are in place. The coils are, of course, designed for this pressure but no insulation is perfect. A small number of electrons is ever present and over years or decades this flow carves out an ever widening pathway through the insulation. This expediential degradation may appear to be sudden when the fault occurs. Another problem, due to constant hot, cold, expansion, contraction, vibration or mechanical impact, is breakage of the fine winding wire. This will not stop the coil from working. The high voltage will simply arc across the gap. The gap will widen as the wire ends melt further apart and soon the adjacent turns will be affected so the coil will eventually fail. Magneto coils are usually a long time dying.
Contact Points
The contact points which are mounted onto the end of the armature shaft, used to time the breaking of the primary winding current, will become pitted and worn, especially so if the capacitor is faulty. The result in high resistance will reduce the current flow in the primary winding and reduce the magnetic flux which adversely effects the secondary winding output voltage.
The Magnet
Lucas Sr4 Magneto Manual Pdf
The permanent magnet can be static, as in the classical horse-shoe form, with the transformer windings rotating between the poles, or sometimes the magnet is mounted on the armature and rotates within the core of a static winding. Jibjab videos free mac. Fallout 4 best weapons mods.
Alnico, the material most often used to fabricate early magnets has a tendency to lose its induced magnetic field over time due to various causes. An importance cause of field strength reduction is the removal of the magnet from its normal situation without fitting a keeper, a device designed to maintain the integrity of the magnetic circuit. Another cause of atom disorientation is mechanical shock, hammer blows or dropping the unit onto a hard surface, etc.
The voltage generated in the primary winding is a product of its velocity through the magnetic field and the strength of that field, so the condition of the magnet is vital for the correct performance of the magneto.
Lucas Sr4 Magneto Manual Diagram
-3068x2455.JPG "Lucas Sr4 Magneto Manual")
Magneto tips
If you are having trouble with your ignition system we recommend that you first change your spark plugs and HT leads. Over time the HT leads can degrade and reduce the potential difference at the spark plug. On many Rolls Royce models there is a dual ignition system. This can mask a fault on these cars as the vehicle will continue to run until the other fails.
Recommendations
If you have identified the magneto as the source of your ignition fault send it to us for repair. We will check all the parts of the magneto for faults and will provide a firm quotation for a repair along with a description of the magneto repair required.
The original coil may be reusable, although it is susceptible to faults - as described in our section: common problems on magnetos. Apple app store mac download.
If the coil has been in service since the magneto was new there is a good chance the insulation has started to break down, allowing voltage to track. We would recommend having the transformer coil rewound as modern class F or H wires and insulations are superior to the ones used at the time it was originally made and would almost certainly give you another 40 years of good service. https://free-lu.mystrikingly.com/blog/mac-command-key-on-windows-keyboard.
Capacitors are replaced with ones that have a longer life expectancy and greater reliability. We always replace the capacitor during a repair as experience has show us that the capacitor tends to be the most unreliable part. If it is an original capacitor then it will almost certainly fail because of its age and the materials and techniques that were used to construct them.
Lucas Sr4 Magneto Timing
Check out our magneto armature winding service. Android file transfer app for mac free download.
