Despite its simplicity, the magneto timing synchronizer, commonly referred to as the magneto timing tool, can be one of the most frustrating tools for even the most experienced mechanic to use. The difficulty of using this tool can be baffling as the theory of operation is as simple as it gets. Connect a lead to the magneto ground point, connect a lead to the p-lead terminal, and as the magneto rotor shaft is turned, a light on the front of the tool will turn on and off as the contact points open and close.
All too frequently, however, a mechanic will struggle with timing a magneto, unable to get the tool to indicate that the contact points of one or both of the magnetos are opening. The typical action is to send the magneto back to Kelly for warranty inspection, only to be informed that the magneto contact points operated perfectly normally when checked on the bench.
This discussion will take a closer look at how the magneto timing light tool can contribute to false diagnosis of a magneto problem.
For the purposes of this topic, the Magneto Timing Synchronizer will be referred to as a Magneto Timing Tool. Of course, this tool has other names, ranging Buzz Box as a nod to the buzzing or whistling sound that backs up the on and off illumination of the timing lights, to other, very salty terms when struggling with the tool on a late Friday afternoon.
From the theory of operation standpoint, the magneto timing tool is not a continuity tester, at least in the conventional sense of how a continuity tester works. The principle of operation for a continuity tester is to introduce a voltage signal to a circuit. If the circuit is open, there will be no continuity and if the circuit is closed or complete, then there is continuity. If used on a magneto, the circuit is open when the contact points are closed, and the circuit is open when the contact points are open.
However, the slight introduction of a voltage is a theoretical safety issue as the voltage from a battery-operated continuity light or a multimeter can charge the electrical circuit and potentially enable it to discharge a spark. So, at some point in the past, a method to passively detect changes to the magnetic circuit of the magneto, or inductance of the magneto electrical circuit, was established to be the correct method. As such, all proper magneto timing tools are based on measuring induction, not continuity.
Inductive magneto timing tools are available in two different styles: mechanical contactor type or solid-state type. Both tools work to the same method of using lights and sound to signal contact point opening and closing, changing the indicating lights and sound based on changes to the magnetic density of the electrical circuit of the magneto.
The gold standard of the mechanical contactor type of magneto timing tool has been the Eastern Electronics E50. Hundreds of thousands of these tools have been produced, and it is virtually impossible to not find this tool in a well-equipped shop. The theory of operation is that the contactors are energized by the internal battery, and when connected to the magneto to detect the contact points are open, the indicator lights will turn ON, and the tone of the tool buzzer changes. The Eastern E50 does not have any instructions on the tool to indicate whether the indicator lights should be on or off when the points open, so the mechanic using the tool must confirm how the lights and buzzer actuate by grounding connecting the contact lead to ground to observe how the tool operates.
The solid-state magneto timing tool works in a similar way, except with no mechanical parts. The sensing of the magneto flux is accomplished strictly by electronics, no mechanical contactors are used. A big difference, though, is the lights turn OFF when the contact points open. The obvious initial concern is that the mechanic using either tool MUST know how it works. The solid-state units have instructions printed on the front that the lights will turn off, or be out when the contact points open.
The timing tool requires specific connections
Countless magnetos are incorrectly determined to be faulty due to the failure of the installer to connect the tool to the magneto correctly. Follow these simple connection rules and the magneto tool will work as required to time the magneto.
Slick magnetos: Connect the tool and use the fiber washer to prevent the tool lead from grounding and causing a false indication on the timing tool that the contact points are grounded and not opening.
The short cover magnetos that use a simple capacitor stud for the P-lead connection require the same fiber washer to ensure that the timing tool lead does not ground and send the wrong signal.
Inspect the magneto with the timing tool BEFORE installation
Step One: Confirm that the tool works before removing and installing magnetos. Low battery voltage, especially with the solid-state tool, can still illuminate the lights, but is likely to not be sufficient to provide enough voltage to sense the change of the magnetic circuit in the magneto. If the tool has not been used for several months, it is a sure bet that the batteries are weak and need to be replaced for accurate operation.
Step Two: Check the magneto for operation BEFORE installing on the engine!! With the magneto on the bench, connect the timing light and confirm that the timing lights illuminate correctly to show contact point opening or closing. In addition, the internal timing of the magneto can very easily be confirmed before installing on the engine.
Insert the timing pin into the distributor gear in the hole that corresponds to magneto ROTATION, not the position on the engine. For example, the right position magneto on a Continental O-200 is LEFT rotation, so the timing pin is inserted into the L hole.
With the pin inserted, the rotor shaft can be moved very slightly. The timing light should turn on and off as the contact points open and close. If the pin has to be removed and the rotor shaft turned 90 degrees so the contact points open and close, then the internal timing is possibly incorrect. The magneto should not be installed until the internal timing is confirmed or corrected.
If the magneto passes the bench test, then it is ready to install.
Bendix Magnetos- 20/200/1200/Dual Magneto Series
Remove the vent plugs on the magneto to expose the red painted gear tooth.
Turn the rotor shaft so that the red painted gear tooth moves within the range of the vent plug hole. The timing light should turn on and off as the contact points open and close. If the rotor shaft is turned 90 degrees so the contact points open and close, and the red gear tooth is not visible in the vent plug hole, then the internal timing is possibly incorrect. The magneto should not be installed until the internal timing is confirmed or corrected.
If the magneto passes the bench test, then it is ready to install.
Final magneto installation and timing
Making a solid ground lead connection between the magnetos and the timing tool is critical. This is the single most often missed step when using timing light tools, and will invariably result in a false diagnosis of magneto timing or incorrect magneto to engine timing.
The magneto timing tool uses a very low voltage to power to power the tool to sense the changes to the magneto magnetic circuit. The ground path from the tool to the magneto has to be direct between the magneto and tool, and as short as possible. If the timing tool ground lead is connected to the engine, it is almost impossible for the tool circuit to complete the necessary ground path through the magneto to properly illuminate lights when the contact points open and close.
The best method to ensure a continuous ground path between BOTH magnetos and the timing tool is to connect an extra jumper lead. Connect the timing tool ground lead to the ground point on the primary magneto. Next, connect a jumper lead to run from the common connection of the timing tool ground on the primary magneto, to the ground point near the secondary magneto contact points. This extra lead provides for a solid ground path and will eliminate the majority of timing problems in which the contact points seem to not open or close as expected.
DO NOT CONNECT THE TIMING TOOL GROUND LEAD TO THE ENGINE OR AIRFRAME! The path to ground may not be connected if there is too much distance between the timing tool ground and the magneto ground.
That’s it for timing tool discussion, give the techniques discussed a try. If you have time, experiment with the tool to see where things can go wrong due to a mistake with a simple connection. As always, feel free to suggest a magneto topic for future discussions.
One of the most common inquiries we receive at Kelly Aero regards ignition harness applications. The basic engine application data is usually easy as most mechanics or owners will know that their airplane has a Lycoming or Continental engine installed, and perhaps they know whether Bendix or Slick magnetos are installed. However, that sort of general information is only partially useful. It is the very specific data on the configuration of the engine and magnetos that defines the correct features of the ignition harness.
So, what information or questions do you need to ask to determine the correct ignition harness for your engine?
#1 What is the engine model?
Invariably, the very first question asked by Kelly Aero Customer Service person is “What is the engine model?” Some customers may start the conversation with “I have a 4 cylinder Lycoming” or maybe they know just part of the engine model or airframe, such as “Lycoming O-320” or “a Continental 550 in a Cirrus”. The issue is that the very specific prefix, engine family and suffix will define the exact harness.
Continental tends to use simple one-letter designators for their engines: O-470-R, IO-550-N, for example. Lycoming uses a system with more numbers in the suffix: O-360-A4A, TIO-360-C1C6D which are good examples. However, the harness fit, lead length, and sometimes special features such as seals for pressurized magneto applications will be different.
The engine model can be found in the engine logbooks or in the Pilot Operating Handbook for the aircraft. The information is also on the engine data plate, but that is only visible when the engine is uncowled.
#2 What is the model number of magneto installed on the engine?
This is another item that requires some specific information. Many customers will say they need a new harness for their “…mags..” with no other details. The current production magnetos are generically referred to as Bendix or Slick, despite the fact that both the Bendix and Slick product lines have been sold by numerous companies. But, Bendix and Slick are the standards, but there are variations within the basic magnetos.
The generic Bendix magneto models fall into the following categories:
20/25/200 Series: Most commonly, all of the compact size Bendix magnetos are referred to as the “20 Series” even though there are variations within the basic 20 Series of the 25 and 200 models. The 20 series are offered in 4 and 6 cylinder versions, but this will be defined by the engine model as the 360 Series Lycoming is always four cylinder and an IO-520 Continental will always be six cylinder, and so on.
1200 Series: the 1200 Series is identified by its large size, and offered in 4 and 6 cylinder versions. The difference between the 20 Series and 1200 Series is that the distributor blocks are much different in size and the ignition harnesses are not interchangeable.
Slick 4300/6300 Series: The Slick magnetos have more rounded features, and a data plate riveted to the side of the magneto, as opposed to the Bendix method of affixing the data plate to the top of the magneto. The Slick harness cap is perfectly round and held to the magneto with three screws. Typically, the Slick ignition harnesses will have a label that denotes the left or right harness part number, and that can be useful in determining the Kelly harness part number.
#3 What size are the spark plugs- 5/8” or 3/4”? Or maybe asked as Small Barrel or Big Barrel plugs?
Historically, this detail trips up most private owners who are trying to buy parts for their airplanes. The spark plug nuts must match the type of spark plug and mistakes made at the time of order will invariably result in buying the incorrect harness.
There are two types of spark plugs: SMALL barrel 5/8-24 or BIG barrel 3/4-20. The numbers refer to the diameter and thread pitch at the top of the spark plug:
Another easy way to determine spark plug nut size is to use a wrench on the flats of the plug. BUT, be careful, as the correct wrench size can be interpreted for the wrong spark plug and harness nut size. A 3/4” wrench does not remove a 3/4-20 nut! Use the illustration below for guidance, but a 3/4” wrench is used to remove a 5/8-24 nut and a 7/8” wrench is used to remove a 3/4-20 nut.
#4 Straight or Elbow leads?
Virtually all modern engine installations use the straight lead, identified by a wire captured in a simple assembly just the small ferrule nut and the larger spark plug nut. A formed tube that guides the wire into the spark plug nut supports the elbow lead.
Straight leads are the industry standard, but Kelly offers the elbow lead for owners who prefer the extra support that the elbow provides. Some aircraft, especially radial engine airplanes and helicopters, prefer to use the elbow harness for extra protection in the slipstream. Current production airplanes with enclosed cowlings make the elbow redundant as the wire is protected within the cowling.
#5 Time to Order
Now that all of the information for engine, magnetos, and spark plug size is known, the Kelly Ignition Harness Application Chart can be used to find the correct harness. On the Internet, navigate to www.KellyAero.com and click on the Support tab, and then Application Chart
The Ignition Harness Application Chart will open and looks like this:
The chart is easy to use, the engine OEM and Models are listed on the left, and magnetos and spark plug sizes are listed along the top. The letter “X’ denotes the column with the applicable magneto and the two far-right columns show the Kelly Ignition Harness part number. As a lookup tip, most of the Kelly harnesses use part numbers similar to the Slick part numbers. Kelly replaces the Slick “M” prefix with the “KA1” prefix. In the example above, KA12772 is a replacement for the M2772 ignition harness.
Here are some examples of what it looks like to find common ignition harnesses:
Lycoming IO-360-A1A, Bendix 20 Series magnetos, 5/8”-24 spark plugs: Harness is a Kelly KA12364, or a KA2364E if the elbows are required.
#6 Half Ignition Harnesses
Sometimes customers will require just a Left Hand or Right Hand side of the ignition harness, just for one magneto. Bendix and Slick use unique part numbers for the Complete, Left Hand and Right Hand harnesses, Kelly Aero uses a simplified system of simply adding an “LH” or “RH” to the basic part number of the harness. A very important note to identify Left and Right: All Left and Right references are from the pilot’s perspective, looking forward through the propeller. The wrong way to determine left and right is to reference left and right from the propeller, looking back at the tail of the airplane.
Here is an example: A Lycoming O-360-A4A, Slick magneto installed on the left position, 5/8”-24 spark plugs. The complete ignition harness is a KA14004, so to order just the Left side, order a KA14004LH.
That is it for the Ignition Harness selection discussion. If you have any questions, call Kelly Sales, Product Support, or send an e-mail to us through the website link: https://kellyaero.com/about/contact-us/
Montgomery, Alabama. March 1, 2021 – Kelly Aerospace Energy Systems LLC, an industry leader in general aviation ignition systems, has announced today that the company will begin operating under a new name and will be known as Kelly Aero LLC, effective immediately. This rebranding strategy consolidates our company name while encompassing our 37-year history in general aviation. The company’s ownership, location, and staff have not changed. Company President, Jeffrey Kelly stated “This rebrand of our company gives us a modern streamlined brand while paying homage to our strong family commitment to aviation. Our core values and commitment to deliver premium quality and value to our customers will continue to hallmark to our success.”
For more information about the name change or to learn more about Kelly Aero LLC please visit: www.KellyAero.com.
About Kelly Aero LLC Kelly Aero LLC is an industry leader with over 37 years of manufacturing and overhauling products for general aviation. Kelly Aero’s facility, located in Montgomery, Alabama, is not only an FAA-approved repair station that overhauls general aviation magnetos, but it is also an FAA MIDO approved Production Approval Holder, with an FAA & OEM approved quality system.
Montgomery, Alabama. March 1, 2021 – Kelly Aerospace Energy Systems LLC, an industry leader in general aviation ignition systems, has announced today that the company will begin operating under a new name and will be known as Kelly Aero LLC, effective immediately. This rebranding strategy consolidates our company name while encompassing our 37 year history in general aviation. The company’s ownership, location and staff have not changed.
Company President, Jeffrey Kelly stated “This rebrand of our company gives us a modern streamlined brand while paying homage to our strong family commitment to aviation. Our core values and commitment to deliver premium quality and value to our customers will continue to be hallmarks to our success.”
For more information about the name change or to learn more about Kelly Aero LLC please visit: www.KellyAero.com.
About Kelly Aero LLC
Kelly Aero LLC is an industry leader with over 37 years of manufacturing and overhauling products for general aviation. Kelly Aero’s facility, located in Montgomery, Alabama, is not only an FAA-approved repair station that overhauls general aviation magnetos, but it is also an FAA MIDO-approved Production Approval Holder, with an FAA & OEM approved quality system.
Kelly Aerospace Thermal Systems has received STC certification for its All-Electric Air Conditioning System for the Mooney R, S, TN, U, and V models. The Electric System offers freedom from flight restrictions and introduces Ground Cooling to the General Aviation Market. You can now call ahead and have your aircraft “Pre-Cooled” without unlocking the cabin.
This 65-pound system is completely installed in the aft section of the fuselage and has a factory look. The cool air is introduced to the cabin from the overhead for more complete cooling. The system has no scoops, therefore, no airspeed penalties so this incredibly fast airplane is still just as fast.
A digital controller allows for carefree operation of the system while managing your flight. The system is only available for 28-volt aircraft for now.
The receipt of the STC was formally announced at the Mooney Summit in Panama City Beach in September 2019.
Ground cooling with GPU.
Piezo switch included for effortless ground startup Minimum of 20° temperature drop in five minutes.
No take-off or in-flight restrictions.
Maximum of 50 amps at peak load, 45 amps at continuous normal operation.
The entire system weighs estimated at 65.6 pounds installed.
System can be operated on the ground, during taxi, takeoff, cruising, and landing.
Cabin-side components occupy only ½ of hat rack compartment leaving remaining space for storage.
AC system integrated into existing headliner distribution ports.
Simple operation via digital display mounted in the control panel.
The system runs using an 11,500 BTU hermetically sealed, 28-volt brushless DC Compressor Motor.
Enjoy some of the recent pictures of our first installation in a Mooney Ovation.