since 1940

Slick Magneto Frequently Asked Questions

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When do you overhaul or replace your magneto - how long should one last

Continued Airworthiness and overhaul information is contained in then manufacturer's maintenance (overhaul) manual.

In the case of magnetos it is specific to the magneto manufacturer, and in some cases, to the aircraft. For example, some Slick Magnetos on some Lycoming IO-540 engines have 200 hour impulse coupling inspection requirements mandated by the manufacturer and an airworthiness directive

Generically, there is a 500 hour inspection requirement for both Bendix and Slick magnetos and a overhaul at engine TBO.

Do I need to remove the magneto gear before returning the core

Slick new magnetos are sold exchange and you must remove the magneto drive gear from the end of the magneto. This is an engine part -- not part of the magneto

Slick magneto showing magneto drive gear. Remove before sending in core

How do I check for a "hot" magneto?

Continental Service Bulletin SB653 (or latest edition) contains information for checking to see if the magneto is "hot".

SB653 in Acrobat format

In addition, the following is provided by Hartzell Propeller

Mag Check
Periodically ensuring that your magneto’s p-leads have not broken is a good defense against unexpected starts on the ground. These leads, which are connected to the ignition (or magneto) switch in the cockpit, are responsible for grounding the mags to keep the engine from running. Sometimes the wires or connections between the switch and the magnetos break or come adrift. In this case, one or both mags may be "hot," or ready to deliver spark whenever the prop is turned. To test them, instead of shutting down the engine in the usual manner with the mixture control, use the key. Allow the engine to cool normally and idle down. Move the key slowly through both Right, Left, and then to the Off position. The engine rpm should drop slightly at both of the individual-mag positions and shut down completely in the Off detent. Allow the prop to stop and then move the mixture to the idle-cutoff position. Do not try to "catch" the engine before it comes to a stop because a dangerous backfire might occur. If the engine does not stop when the key is in the Off position, shut it down with the mixture, prominently mark the prop as being "hot," and contact maintenance personnel immediately.

There are a few other caveats to consider when in the vicinity of the prop.

Avoid pulling the airplane around by the prop. Yes, this seems the perfect solution to a vexing problem of how to change the airplane’s position without having to walk around and get the tow bar, but it’s worthwhile to make the extra effort. Neither the engine nor the prop particularly benefit from the loads imposed by horsing the whole airplane around.
Avoid pushing the airplane by the spinner. The spinner and backing plate are built to be light, so they’re quite fragile. Pushing on them can cause the backing plate to crack and can lead to spinner failure.
Avoid contact with prop deice boots and associated wiring. If you want your hot prop to be toasty when it counts, stay clear of the boots.

How to I know if the magneto capacitor is working?

See my article Checking the aircraft magneto capacitor

Do I need a noise filter on my Slick Magneto

No, Slick magnetos (and the newer Bendix SC series) have feed-thru capacitors that act as built-in noise filters. Adding an external noise filter such as the MF-3  reduces magneto output.

Slick Magneto MF-3A magneto ignition filter

How do I subscribe to Slick Maintenance Manual?

You purchase the F-1100 Master Service Manual directly from Unison. Included is a one year
revision service.

Subscription Service Order Form

What was the Slick "Throw-away" magneto? Are any parts available

Slick made a magneto in the 1960's and possibly early 1970's that was a throw-away magneto.

To quote from Slick Service Bulletin 2-69 " ...it is recommended that you remove the Magneto at 900 hours... available at your Fixed Base Operator, at the exchange price of $40.00"

For $40.00 it didn't pay to repair or mess with them. There never was any repair parts available for them.

Some of these magnetos are still in service. These are the 4000 series magneto such as the 4001.

What is the difference between Slick and Unison magneto?

They are the same. Unison Industries purchased Slick Magneto back in the 1970's.

How do I time the Slick magneto

Download Timing instructions for the Slick Magneto 860KB
This download program includes the instructions below plus the timing instructions from the Slick Maintenance Manual. Download the program and then click on it to execute.

WHERE DO I STICK THE TIMING PIN?
 

1. TIMING INSTRUCTIONS ARE ON THE OUTSIDE OF THE BOX.

INSERT THE T-118
TIMING PIN IN THE L OR HOLE OF THE DISTRIBUTOR BLOCK, DEPENDING UPON THE ROTATION OF THE MAGNETO. REFER TO THE MAGNETO DATA PLATE FOR MAGNETO ROTATION

2. TURN THE ROTOR SHAFT OPPOSITE THE SPECIFIED DIRECTION OF ROTATION UNTIL THE TIMING PIN IS INSERTED APPROXIMATELY 7/8" INTO THE DISTRIBUTOR BLOCK. WHEN PROPERLY ENGAGED, THE TIMING PIN WILL "SEAT" AGAINST THE DISTRIBUTOR BLOCK. NOTE: IF THE ROTOR SHAFT CANNOT BE TURNED AND THE TIMING PIN IS NOT SEATED 7/8" INTO THE DISTRIBUTOR BLOCK, REMOVE THE PIN. TURN THE ROTOR SHAFT 1/8" TURN AND REINSERT THE PIN. TURN THE ROTOR SHAFT 1/8" AND REINSERT TIMING PIN. THEN REPEAT STEPS 1 AND 2 ABOVE

3. WITH THE PIN FULLY INSERTED INTO THE DISTRIBUTOR BLOC,, THE MAGNETO IS NOW ALIGNED TO FIRE CYLINDER NO 1.

4. AFTER THE MAGNETO IS INSTALLED ON THE ENGINE, REMOVE THE TIMING PIN. PROCEED BY FOLLOWING ENGINE MANUFACTURER'S TIMING PROCEDURES.

Many thanks to Steve for posting this article on the Sky Ranch Engineering Forum!

Here is some of the basics for Magneto Timing. Hope this helps.

Can someone explain to me in laymen's terms how to set engine timing (Continental) and magneto timing (Slicks)? Thanks!

It is pretty simple. There are two kinds of timing that have to be taken care of with a magneto. There is the internal timing and the external timing. The internal timing is done on the bench with the magneto out of the engine. You have to ensure that the points open at the correct spot in the magneto revolution in reference to the E-gap. There is usually a set of markings on the magneto to help you get this properly lined up. Then set the point gap and opening correctly by adjusting the point position relative to the rotor. Once the internal timing is correct the magneto should put out a good hot spark. If the internal timing if wrong, the magneto will put out a weak spark or even no spark at all.

With the Slick magneto there is a hole in the case. You put a timing pin into this hole to lock the magneto in position with the points just opening at the E-gap. This, of course, depends on the proper internal timing of the magneto.

Then you bring the number one cylinder to top dead center. You can do this by putting a special plug into the cylinder that stops the
piston from coming all the way to the top. Put your degree ring on the spinner or prop and read the setting where the piston stops with BOTH VALVES CLOSED. Then rotate the engine back the other way until it hits the stop again. Read the setting there. Top dead center is halfway between those two readings. Adjust the degree ring so that the zero reference is halfway between those two positions. Now you have your degree ring set.

Remove the blocking plug from the spark plug hole and rotate the engine in a forward direction until you are coming UP toward the
zero reference mark on the compression stroke on number one cylinder. Stop at exactly the correct advance setting prior to top dead center. If you go past the point, continue forward two more revolutions until you stop on the correct advance setting while turning the prop in the correct direction. Needless to say, you want to do all of this turning of the prop with the spark plugs removed from the engine. We would NOT want it to START while we were playing with the prop!

With the engine positioned at the point in its rotation where you want the magneto to fire, and the locking pin in the Slick magneto, insert the magneto into the proper location on the accessory case. Do not force it, but let is slide into engagement with the gear that drives it. Snug the magneto down in position. Now your timing is approximately correct, both internal and external.

Follow this procedure for both magnetos:

Now, with both magnetos installed, connect your magneto timing box to the p-leads of the two magnetos. Rotate the prop again, once more in the proper direction, two revolutions. As you come up on the second revolution, watch the degree ring carefully. The lights on the buzz box should switch at the proper advance point for both left and right mags. The buzz should let you know the status also.

When both mags are exactly right, as driven forward by the engine gearing with all slack taken out in the direction of rotation, you can disconnect your buzz box and reinstall the plugs and ignition wiring. Make sure the P-leads are properly connected to the ignition switch and are grounded when the mag is switched off.

Some engines do NOT have adjustable magneto mountings. These magnetos have to have adjustments made to the timing by repositioning a splined coupling in the magneto drive shaft. There are a different number of splines on both sides of the coupling and by going forward on one side and back on the other side of the coupling you can make small and precise adjustments in timing. The shaft timing is not likely to change if you do not remove the magneto. However, the magneto timing will still change as the rubbing block on the points wears down with use. That is the primary reason that you recheck the magneto timing at every annual inspection.

We will start out with the installation of the magneto since this may be the most confusing area, leading to the most starting problems, etc. based on the calls and letters we receive. The older style, 4050 and 4051, "throw away" models probably should be traded in on the newer 4350 and 4351 rebuildable mags. They are more reliable, more readily obtainable, and are easily repaired or rebuilt even by the owner/builder. Basically the differences between the original "throw away" and rebuildable mags is size. The "throw away" being smaller than the rebuildable. Also, when timing the magneto, prior to installing on the engine, you must "spark out" the "throw away" model by spinning the timing gear to set the magneto on cylinder number one. On the newer, rebuildable magneto's, Slick supplies a little "pin", a T-118 timing pin, which is used to set the magneto timing to the number one cylinder. With the distributor cover off, look into the forward end (on a EZ!) of the mag, you will see two holes in the plastic molding, the top one marked for left hand rotation (L), the bottom on for right hand rotation (R). Look on the data plate on the body of the mag for its direction of rotation. Left rotation is normal for a Lycoming O-235, O-320, or O-360. Now, gently push the timing pin into the hold marked (L) until it bottoms. Rotate the timing gear on the shaft of the mag opposite the direction of normal rotation until you feel the pin drop into a hole.

If you have to rotate the magneto very far, you will feel the timing pin trip over a bump inside the mag. Don't force it to rotate. Gently back the timing pin out a 1/4" or so to clear the bump, rotate the shaft and gently push the pin back in. Continue rotating until the pin locates in the hole. The magneto is now internally set on cylinder number one. It is not a bad idea to tape the pin in place with a piece of masking tape. In any case, the pin must remain in this position, without the distributor cover installed, until the magneto is actually in place on the accessory case.

Now, you must set your engine at 25 degrees before top dead center on the number one cylinder (or whatever angle your data plate calls out, 28 degrees for O-235-L2C). Remove the top spark plug from the number one cylinder, hold your thumb over the hole and rotate the engine in the direction of normal rotation until you feel pressure under your thumb. Continue rotating the crankshaft until the advance timing mark (20, 25, or 28 degrees, check your data plate) is exactly opposite the small hole located at the 2 o'clock position on the front face of the starter housing. (This is for Lycoming engines with a starter and starter ring gear installed.)
NOTE: If the prop is accidentally turned in the direction opposite normal rotation, you must repeat the above procedure since accumulated backlash in the timing gears will make the final timing incorrect.
At this point, the engine is ready for assembly of the magneto's. With the timing pin still in place, carefully fit the magneto into its hole. When it sits flush on the machined surface of the accessory case, pull the timing pin out (rotating the prop at this point may shear the timing pin off) and, while holding the mag firmly in place, install the toe clamps, flat washers, lock washers and nuts and tighten until finger tight. Repeat for the other magneto, being certain that the prop has not moved.

Use a battery powered magneto timing light such as a model E50 from Eastern Electronics.. Connect it to a convenient engine case bolt (ground) and to each magneto terminal (the same stud your mag switch is connected to). If the mag switches are wired up, you will have to make both mags "hot" (mag switches to the normal engine running position even though the distributor cover is not yet installed). Make sure the fuel valve is off and the mixture is at idle cut off, and always treat the prop as you would a loaded gun!)
Rotate each magneto in its housing until the timing light comes on. Now slowly turn it in the opposite direction until the light goes out. Slowly turn the magnetos forward again until the timing light just goes on. Tighten the nuts a little.

Now, back the prop off enough to turn both timing lights off. Slowly bring the prop back in the direction of normal rotation until both lights come on. They should come on simultaneously, or very close to it. Now check and see if the appropriate timing mark on the starter ring gear is in perfect alignment with the hole in the starter housing. If it is, tighten the magneto hold-down nuts firmly (maximum torque is 150 inch/lbs., minimum is 110 inch/lbs.). Recheck that the timing lights come on together at the proper time and you are ready to install the distributor caps. If you are working on a Long-EZ, this is the hard part! The distributor covers are so close to the firewall that a 90 degree screwdriver must be used on the standard Slick screws. Believe it or not, this can take an hour or more to do! The Allen head screws Mike called out in CP 54 make this job easy (less than 30 seconds per screw) and he still has a supply of stainless steel Allen head screws suitable for this job. Send $1.00 plus a SASE for 6 screws.

There you have it! If your airplane has a Lycoming engine and no starter or We will start out with the installation of the magneto since this may be the most confusing area, leading to the most starting problems, etc. based on the calls and letters we receive. The older style, 4050 and 4051, "throw away" models probably should be traded in on the newer 4250 and 4251 rebuildable mags. They are more reliable, more readily obtainable, and are easily repaired or rebuilt even by the owner/builder. Basically the differences between the original "throw away" and rebuildable mags is size. The "throw away" being smaller than the rebuildable. Also, when timing the magneto, prior to installing on the engine, you must "spark out" the "throw away" model by spinning the timing gear to set the magneto on cylinder number one. On the newer, rebuildable magneto's, Slick supplies a little "pin", a T-118 timing pin, which is used to set the magneto timing to the number one cylinder. With the distributor cover off, look into the forward end (on a EZ!) of the mag, you will see two holes in the plastic molding, the top one marked for left hand rotation (L), the bottom on for right hand rotation (R). Look on the data plate on the body of the mag for its direction of rotation. Left rotation is normal for a Lycoming O-235, O-320, or O-360. Now, gently push the timing pin into the hold marked (L) until it bottoms. Rotate the timing gear on the shaft of the mag opposite the direction of normal rotation until you feel the pin drop into a hole.

If you have to rotate the magneto very far, you will feel the timing pin trip over a bump inside the mag. Don't force it to rotate. Gently back the timing pin out a 1/4" or so to clear the bump, rotate the shaft and gently push the pin back in. Continue rotating until the pin locates in the hole. The magneto is now internally set on cylinder number one. It is not a bad idea to tape the pin in place with a piece of masking tape. In any case, the pin must remain in this position, without the distributor cover installed, until the magneto is actually in place on the accessory case.

Now, you must set your engine at 25 degrees before top dead center on the number one cylinder (or whatever angle your data plate calls out, 28 degrees for O-235-L2C). Remove the top spark plug from the number one cylinder, hold your thumb over the hole and rotate the engine in the direction of normal rotation until you feel pressure under your thumb. Continue rotating the crankshaft until the advance timing mark (20, 25, or 28 degrees, check your data plate) is exactly opposite the small hole located at the 2 o'clock position on the front face of the starter housing. (This is for Lycoming engines with a starter and starter ring gear installed.)

NOTE: If the prop is accidentally turned in the direction opposite normal rotation, you must repeat the above procedure since accumulated backlash in the timing gears will make the final timing incorrect.
At this point, the engine is ready for assembly of the magneto's. With the timing pin still in place, carefully fit the magneto into its hole. When it sits flush on the machined surface of the accessory case, pull the timing pin out (rotating the prop at this point may shear the timing pin off) and, while holding the mag firmly in place, install the toe clamps, flat washers, lock washers and nuts and tighten until finger tight. Repeat for the other magneto, being certain that the prop has not moved.

Use a battery powered magneto timing light such as a model 2E from Sky Ranch). Connect it to a convenient engine case bolt (ground) and to each magneto terminal (the same stud your mag switch is connected to). If the mag switches are wired up, you will have to make both mags "hot" (mag switches to the normal engine running position even though the distributor cover is not yet installed). Make sure the fuel valve is off and the mixture is at idle cut off, and always treat the prop as you would a loaded gun!)
Rotate each magneto in its housing until the timing light comes on. Now slowly turn it in the opposite direction until the light goes out. Slowly turn the magnetos forward again until the timing light just goes on. Tighten the nuts a little.

Now, back the prop off enough to turn both timing lights off. Slowly bring the prop back in the direction of normal rotation until both lights come on. They should come on simultaneously, or very close to it. Now check and see if the appropriate timing mark on the starter ring gear is in perfect alignment with the hole in the starter housing. If it is, tighten the magneto hold-down nuts firmly (maximum torque is 150 inch/lbs., minimum is 110 inch/lbs.). Recheck that the timing lights come on together at the proper time and you are ready to install the distributor caps. If you are working on a Long-EZ, this is the hard part! The distributor covers are so close to the firewall that a 90 degree screwdriver must be used on the standard Slick screws. Believe it or not, this can take an hour or more to do! The Allen head screws Mike called out in CP 54 make this job easy (less than 30 seconds per screw) and he still has a supply of stainless steel Allen head screws suitable for this job. Send $1.00 plus a SASE for 6 screws.

There you have it! If your airplane has a Lycoming engine and no starter or starter ring gear installed, you will need a timing indicator such as model E25 and a top dead center locator or an equivalent protractor-type indicator.

This type indicator fits onto the spinner or prop (does not need to be centered) and has a weighted pendulum-type pointer. Use the top dead center finder in the top spark plug hole on cylinder number one, set the protractor indicator so the pointer points at 0 degrees or top dead center (TDC), then turn the prop backwards to about 35 degrees before TDC, then come slowly forward to 25 degrees (or 28 degrees) to be certain to get rid of all backlash.
starter ring gear installed, you will need a timing indicator such as model E25 and a top dead center locator (both available from Aircraft Spruce) or an equivalent protractor-type indicator.

This type indicator fits onto the spinner or prop (does not need to be centered) and has a weighted pendulum-type pointer. Use the top dead center finder in the top spark plug hole on cylinder number one, set the protractor indicator so the pointer points at 0 degrees or top dead center (TDC), then turn the prop backwards to about 35 degrees before TDC, then come slowly forward to 25 degrees (or 28 degrees) to be certain to get rid of all backlash.

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Disclaimer: sacskyranch.com contains abundant information relating to aircraft maintenance. The information provided  is not intended to supercede or supplement the F.A.A. approved  maintenance and/or operator’s manuals. Those F.A.A. approved manuals must be utilized when performing maintenance and/or operating aircraft.