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 Our approved scope of work includes the list of makes and models of 4 and 6 cylinder magnetos, shown at the bottom of this page, for 500 hour inspection and overhaul.

If you want us to carry out  component maintenance on your magneto(s), we will need a Work Order. We can accept a Work Order from another maintenance organisation or CAMO - in which case they will use their own form or if you are an aircraft owner you can download ours and use that.

Note: do not send us magnetos without having first contacted us and discussed your requirements and without our acceptance of your work order. Acceptance depends on parts availability  etc.

All maintenance is done in accordance with the Manufacturer's Instructions for Continuing Airworthiness (ICA) and applicable Airworthiness Directives and Service Bulletins. For our scope of work that means:

Champion Aerospace/ Slick L1363J  and L1073H and Kelly Aerospace M-001 maintenance manuals.

The onus is on the CAMO or aircraft owner to determine what maintenance is required - e.g. is the magneto due a 500hr inspection or overhaul? We do not have access to the aircraft maintenance records and do not know how many hours the magneto has clocked up. The magneto manufacturers specify that a magneto shall not exceed the TBO of the engine on which it is mounted. It is not advisable to get 500hr inspections done continually - 3 should be the limit before an overhaul or replacement with a new one. The Slick and Kelly Aerospace component maintenance manuals both specify a time in service limit of 12 years. Owners of permit aircraft need to be very careful about this. They are responsible for deciding what maintenance to request from us and it may be that they should be requesting an overhaul rather than a 500 hour inspection for the reason given above.

500 Hour Inspection

Every 500 hours, the magneto should be removed from the engine and inspected in accordance with the component maintenance manual. A typical GA magneto will only undergo 3  No 500 hour inspections when installed on a particular engine as the magnetos accompany the engine for overhaul  when it reaches TBO (typically at 2000 hours).The various parts are cleaned and inspected for cracks, corrosion, damage and dimensions. The capacitor (condenser) is checked for capacitance and the coil primary and secondary windings are checked for resistance and insulation resistance. Anything which is found to be defective or not within specified limits is replaced - hence IRAN - Inspect and Repair As Necessary.

Turnaround time for 500 hour inspections is less than a week (usually 1to 2days) as we carry a stock of parts but obviously if parts other than those which usually need replacement are defective, then there may be a lead time for those parts. 

Typically we replace the following during a 500 hr:

Contact /Points Kit - Rotor Gear - Distributor gear carbon brush.

Overhaul

The magneto is dis-assembled. The manufacturers specify a list of parts which must be replaced during overhaul - regardless of condition. This means that the only original parts remaining after an overhaul will be the frame/housing and the rotor (and that is subject to those items passing inspection!). We can only use new parts to replace these and therefore the cost of an overhaul could approach that of a new magneto.

As per Section 4.0 of the Champion/Slick Magneto Maintenance and Overhaul Manual  (L1363J), an overhaul must be done if any of the following events occur:

• Lightning strike on the aircraft
• Sudden engine stoppage
• Propeller Strike
• Immersion

Time in Service allowance

For Champion/Slick magnetos (again Ref Section 4.0 of L1363J), the TIS allowance is the Engine TBO or 12 years. Many GA aircraft have very low utilisation rates and clearly if the utilisation is less than an average of 41 hours per year,  the TIS allowance will be exceeded before a 500 hour inspection is due. This is easily overlooked. Also 4200 series magnetos with a TIS of 1000 hours or more will require both bearings to be replaced.

After both a 500hr Inspection or an overhaul, the magneto is tested on the test bench. This verifies that the magneto is producing sparks  and in the case of an Impulse Coupling Magneto, that the IC operates over the correct speed range (i.e. cuts out when it is meant to). There is also an optional long term test where the magneto is run for 3 hours and the surface temperature is checked. An additional charge will be applied if this is specified in the Work Order. 

Release to Service:

On completion we will issue EASA Form 1 (at latest revision) for 500 hour Inspection or Overhaul or Repair as applicable.

Note that the re-installation of the magneto on the engine must be covered by a separate CRS from the Engineer or maintenance organisation who is installing the magneto.

(We can if requested fit the magneto to the engine and time it. This is not covered by the EASA Form 1 for component maintenance and will be subject of a separate CRS as mentioned above and subject to a separate charge for travel and installation).

The magneto is timed internally during component maintenance but still has to be externally timed to the engine during installation. The correct gasket and fasteners must be fitted when the magneto is re-mounted on the engine. Drive gears are not supplied by us and if sent with magnetos for maintenance, drive gears will be returned but cannot, and will not, be covered by the EASA Form 1 issued for the magneto.

Video: 4381 Magneto on test post overhaul:   https://youtu.be/j1Su7txIhj8

    Electrical tests on Magneto components during 500 hr inspection:      https://www.youtube.com/watch?v=kbPJyGB5NVk

 External Timing of the Magneto to the Engine

Before the magneto and engine can be returned to service, the magneto must be timed to the engine. The internal timing of the magneto has been done during 500 hr inspection/overhaul. This ensures that the magneto points open when the rotor magnet is in the "E-gap" position - where the magnetic field strength/flux is highest and results in the best possible spark. External timing is about making sure that the magneto fires at the correct point in the engine operating cycle. That point will be stated on the engine data plate e.g. 20 degrees before Top Dead Centre Compression (BTDC).

This is a relatively simple task but many people get confused by it:

(Slick and Kelly Aerospace Magnetos)

(1) Set up the engine so that the piston in No 1 cylinder is at the specified number of degrees before Top Dead Centre  on the Compression stroke.

• The engine cylinder numbers are cast into the crankcase - usually odd numbers on one side and even on the other side of the engine.
• Compression stroke is the one with the piston moving up the cylinder with inlet and exhaust valves closed and squeezing the air in the cylinder.
• Remove the top spark plug in all cylinders to stop the engine firing unintentionally while timing it  and to allow you to see the pistons motion.
• By putting your finger/thumb on or just over the spark plug hole on No 1 cylinder, you will feel air being driven out of the cylinder on the compression stroke.
• Note that the piston moves up the cylinder on the exhaust stroke as well as on compression and there may be some air escaping through the spark plug hole as well as through the exhaust valve (which will be open) but no pressure will be built up with your finger on the spark plug hole if it is the exhaust stroke.

(2) Rotate propeller in normal direction of engine rotation until the timing marks on the ring gear (if there is a starter motor!) or crankshaft flange line up with the hole in the starter motor housing or the crankcase  joint (see engine/airframe manual). Engine is now set up in the firing position. Do not move the propeller after this point. Note though that just because the timing marks are lined up, it does not mean the engine is set up correctly - the marks will line up during the exhaust stroke as well and it is compression stroke that is required.

(3) Offer up the magneto to the mounting pad on the engine accessory case with any necessary spacer/adaptor and gasket. Magneto should be roughly in an upright position. Attach the clamps and nuts and tighten finger tight only.

(4) Take the synchroniser/magneto timing light. Connect the black wire/crocodile clip to a good earth. Connect either the red or green wires (Red for Port/Left  and Green for Right/Starboard) to the "P"-lead stud (i.e. the capacitor stud). Switch on the synchroniser.  There are 2 types. One where the lights/buzzer goes on when the points open and one where the lights/buzzer are extinguished when the points open. Make sure you know which one you are using. Assuming the former type, when you switch the synchroniser on, the lights will probably be on and the buzzer will sound. Rotate the magneto body until the buzzer/light goes out. The points are just opening now and the clamps should now be tightened. 

(5) Tighten the clamp nuts to the specified torque in stages and evenly from side to side. Over-torque will break the magneto flanges making it useless as  a core unit for exchange purposes.

(6) Rotate propeller in both directions around the timing marks to verify that timing lights go out and come back on either side of the timing point.

(7) Re-fit the harness cap.

Harness Cap

On Slick Magnetos the harness cap is attached by 3 No screws. These screws are not evenly spaced around the circumference and at the same time the ignition leads have to fit into the towers on the distributor cap. This makes it impossible to fit the cap in the wrong position on the magneto. However harness caps are specific to a particular engine. The distributor in the magneto will always fire towers in the same order for a given direction of rotation. Which cylinders leads are fitted in which tower is determined by the harness cap  which means the firing order will be wrong if you fit the wrong harness cap to the magneto.

Some engines are set up for the left magneto to fire the top plugs on the right hand cylinders and the bottom plugs on the left hand cylinders and vice versa fo rthe right magneto. Others have the left mag firing all of the bottom plugs an dthe right mag firing all of the top plugs. 

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