Unison magneto troubleshooting

Feb. 1, 1999

Unison Magneto Troubleshooting

By Harry Fenton

February 1999

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With more than one quarter million products in the field, the Unison Industries Slick Aircraft Products Customer Service Department is contacted by scores of customers on a daily basis to provide answers to a wide variety of magneto, ignition harness, LASAR® and SlickSTART™ issues. While each situation is different and no two customers are quite alike, there are many frequently asked questions that are discussed on a repetitive basis. Interestingly, it is the most basic issues that consume the bulk of the Customer Service Department time in handling customer issues.

The following article provides some insight into the most common magneto and ignition harness questions received by the Unison-Slick Customer Service Department. Even though some of the issues presented here are fairly basic, the fact that so much of the Slick Customer Service Department's time is spent discussing these topics indicates that even basic issues are not as clear cut as they may seem.

What are all of these holes for?
The Slick distributor block is common to both conventional and LASAR™ magnetos, and is aligned, or "pinned", depending upon magneto rotation. The "L" and "R" hole correspond to rotation of the magneto, not the placement of the magneto on the engine (See Figure 1). Rotation can be determined one of two ways. First the dataplate has a box labeled "ROT" with either and "L" or an "R" embossed into the box (See Figure 2). Observe the direction that the rotor shaft needs to be turned to engage the impulse coupling: Left rotation magnetos engage the impulse coupling by turning the rotor shaft counterclockwise, right rotation magnetos engage the cimpulse coupling when the rotor shaft is turned clockwise (See Figure 3).

Incidentally, the "X" hole is for timing the LASAR electronic magnetos and different rules apply. Contrary to the directions for standard magnetos, never pin the LASAR magneto according to rotation; simply use the X hole for LASAR magneto pin set-up.

Inserting the timing pin
The most basic element of timing a Slick magneto is the insertion of the timing pin to align the distributor finger to tower number one in the distributor block.

Note that there are a couple of steps machined into the body of the T-118 timing pin (Figure 4). The first step of the T-118 is seated flush against the surface of the distributor block and should be oriented vertically in relation to the distributor towers.

With the T-118 inserted (Figure 5), the rotor shaft should have some free play to turn about 5-10 degrees left or right. If the rotor shaft is held firmly fixed, or if the T-118 is inserted tightly into the block at an angle with no detectable movement, then there is a problem.

Check to make sure the T-118 is not bent prior to insertion (Figure 6). Even a slight bend can allow the T-118 to "hunt" and possibly slide into the wrong hole.

Also, when the rotor shaft is being turned to find the correct hole for insertion, you will notice several points where the T-118 gets wedged and must be pulled outwards slightly to clear the obstruction (usually the distributor finger of the balancing block, Figure 7).

Do not force the T-118 into the block and gear assembly. When the distributor gear hole and the distributor block hole are aligned, the T-118 should slide into place with little or no force.

Do not remove the vent plug to look for timing marks to insert the timing pin or spark out the magneto to find distributor tower number one. This method is applicable only to the 4000/4100 series magnetos and a lot of expensive shop time can be wasted trying to apply these techniques to the newer 4200/6200 and 4300/6300 series magnetos.

The most common problem
It is amazing how many calls are received by the Slick Customer Service Department related to a magneto that is being installed into a position on the engine that is opposite of magneto rotation. For example, virtually all Lycoming four cylinder engines and all TCM O-200 engines use left-hand rotation magnetos for both the left and right position magnetos. Frequently, an installer is working on a problem with the magneto positioned on the right side of the engine that is running rough or developing high rpm loss. The obvious question to ask is "Was the magneto pinned properly before being installed on the engine?"

Slick T-118 timing pin is inserted into holes in the distributor block appropriate to magneto rotation to lock the distributor finger to align with tower number one. The engine is positioned to the advance firing position on cylinder number one, the pinned magneto is installed on the engine, and a timing light is connected to synchronize the contact point opening to the engine advance position. Here's the catch: If the magneto is pinned incorrectly, the contact points can still be synchronized to the engine firing point, but the distributor finger is positioned over the wrong tower. This can lead to a confusing condition where the contact points seem to be synchronized, but the engine runs poorly on the subject magneto.

As a matter of routine, Slick Tech Reps usually direct the installer to remove the offending magneto, ensure that it is pinned correctly, and reinstall the magneto. Ninety percent of the time this fixes the problem and the customer happily disappears off into the sunset.

Timing Tool
Once pinned, the magneto is now ready to be synchronized to the engine using a magneto timing light (Figure 8). Typically, there are three leads running from the timing light; two leads run to each magneto p-lead connection and the third is a ground lead that is connected to a grounding point common to the magneto being timed.

Before installing the magneto on the engine, a lot of time can be saved up front by ensuring that the magneto and timing tool are working together. Connect the timing light to the magneto and confirm that the contact point synchronization lights go on and off. If the points do not appear to be opening or closing, confirm that the batteries to the tool are providing adequate supply voltage. Use only alkaline batteries! Cheap or weak batteries do not provide enough milliamps and affect the tool's sensitivity to contact point opening.

Be certain that the p-lead connection from the tool is not grounding on the magneto frame.

Always have the fiber washer installed when the timing tool alligator clip is attached to the p-lead. Many timing problems can be traced back to the clip simply by finding ground at the p-lead connection (Figure 9), which can result in a magneto that is stubborn to provide point opening indications.

If the batteries and connection are sound, snap the magneto through two or three times to burn off any contamination that might be present on the point faces. Be careful not to snap the magneto too many times without a sparkplug attached to receive the load, otherwise the magneto coil may be damaged. If the problem continues, connect the tool to another magneto to see if the problem follows the tool or is a condition limited to the magneto in question.

Once the magneto is installed on the engine and ready to be timed, connect the ground lead from the timing tool to the magneto being timed. If the ground lead is attached to the center of the engine, sometimes the ground path is too difficult for the timing tool circuit to complete.

Setting up E-gap
Setting up the internal timing of the Slick magneto is easy and accurate, as long as the correct procedures are used. Most problems related to internal timing are related to the improper use of the Slick timing tools.

For many years, the standard tool used to set-up the E-gap of the Slick magneto was the T-100 timing tool (Figure 10). The T-100 is a combination base and pressing tool used to disassemble and time the magneto.

The old method of timing Slick magnetos specified that the timing disc on the T-100 baseplate (Figure 11) be set up to a certain number of degrees appropriate the particular magneto model being timed. Once the base plate was set, the impulse end of the magneto was engaged into the slots on the reverse side of the timing disc. The frame of the magneto was then rotated until the left side of the frame contacted a stop pin in the base of the T-100 (Figure 12). This method positioned the rotor shaft into E-gap, and the contact points would then be adjusted to just break open.

It was an easy-to-use method, but somewhat inaccurate. The basic problem was that due to the stackup of tolerances that could occur when referencing from the impulse end of the magneto up to the contact points, achieving the proper e-gap setting sometimes proved difficult. Subsequently, a more accurate method was devised. Also, mechanics would sometimes set up the disc to a degree number not applicable to the magneto that was being serviced. For example, the T-100 timing method was applicable to the 4200/6200 series impulse magnetos only, consequently, there are no approved procedures provided by Slick to use the T-100 to set up the E-gap on 4300/6300 series impulse coupled magnetos.

During the late '80s the rotor shaft for the Slick magneto was changed to incorporate slots to accommodate the Slick T-150 E-gap gauge (Figure 13). The T-150 E-gap gauge inserts into the rotor shaft and provides for extremely accurate positioning of the rotor shaft.

The notched end of the E-gap gauge inserts into a slot in the rotor appropriate to the magneto rotation. With the T-150 inserted, the rotor shaft is turned in the direction indicated by the arrow cast into the rotor head next to the slot for the T-150 (Figure 14). When the tool contacts the frame (Figure 15), the rotor is set in the E-gap position and the contact points are then adjusted to just break open.

After the E-gap has been set, remove the tool, turn the rotor shaft to position the cam to the highest point of lift, and use a feeler gauge to check the point gap opening. The point gap range is .008" to .0012".

Never set the contact points by just using a feeler gauge! Setting the contact points to a particular gap setting does not accurately position the rotor shaft to optimize E-gap. Always use the T-150 tool to set E-gap first, and then use the point gap measurement to determine the go/no go condition of the contact points. If the point gap falls outside of the specified range, then the point and cam combination are worn beyond limits or the internal e-gap set up was done incorrectly.

The E-gap gauge can also be used on older rotors, but some of the visual prompts are different. Older rotors feature a cutout area between the lamination stacks in the rotor head. The flat end of the tool is inserted against the edge of the lamination stack and the rotor is turned to wedge the tool against the left side of the frame for left rotation magnetos and against the right side of the frame for right rotation magnetos. With the tool in place, the contact points are adjusted and checked for go/no go condition using the method described above (Figure 15).

Ignition Harness
Ignition harness issues usually relate to left and right orientation, the size of the nut that fits the sparkplug and the overall fit of the harness to the engine.

First, the reference point for left and right is always from the pilot's perspective, so the left and right portions of the ignition harness should be installed accordingly. Most Lycoming engines and the TCM O-200, O-300, E-series, and IO-360 series are all configured with magnetos that attach to the rear of the accessory case. The magnetos for the TCM 470, 520, and 550 series engines are mounted on the top of the engine facing forward. The pilot's perspective rule still applies, so route the ignition harness accordingly.

Unison Magneto Troubleshooting

By Harry Fenton

February 1999

The Slick ignition harness spark plug nuts are permanently labeled for position on the engine, e.g., the nut marked "T1" routes to the top spark plug in cylinder number one.

Frequently, the installing mechanic will use the previous harness as a guide to install the replacement harness and finds that the new harness does not fit or route like the one removed. The common assumption is that the new harness was manufactured incorrectly.

But, are the old and new harnesses identical in the way that they are laid out for routing? Engine and airframe manufacturers have specified different routing schemes to address rough running, cable routing, or other issues. In fact, Lycoming issued Service Instruction 1294 to detail alternate ignition cable routing for their four cylinder engines. Ultimately, Slick manufactures ignition harnesses to the engine manufacturer's specifications, so the engine OEM has determined the best lead lengths and routing for the leads. The bottom line: Route the replacement Slick harness as it is marked for left and right location and spark plug placement.

Also, be careful of using the cylinder numbers embossed on the case of the engine for lead placement. Sometimes the baffling can obscure an embossed number causing the ignition lead to be installed on the wrong cylinder. The TCM O-200 is a classic example of an installation that suffers a disproportionately high number of problems due to the placement of the embossed number on the engine case (Figure 16).

Choosing between an ignition harness configured for 5/8-24 or 3/4-20 sparkplugs can cause some confusion, too. Slick spark plug insulators provide the easiest clue: green insulators denote 5/8" plugs and red insulators are used on 3/4" plugs (Figure 17).

There are also some general rules associated with spark plug configuration: a 3/4" wrench fits 5/8"-24 ignition lead nuts, and a 7/8" wrench issued to remove 3/4"-20 nuts. If Champion spark plugs are used, the part number embossed on the spark plug will begin with REM for a 5/8' plug, and RH for a 3/4" plug. Auburn used SR to denote 5/8" and HS to denote 3/4" plugs.

Most Lycoming four and six cylinder engines leave the factory with 5/8" plugs, and the turbo'd engines are configured with 3/4" plugs. The TCM O-200, O-300, and GO-300 engines typically use the 5/8" plug. All TCM 360, 520 and 550 series engines use the 3/4" plug. The wild card is with the 470 and E-series engines. There seems to be a 50-50 chance between the two plug types.

If possible, always visually check the engine for plug type as virtually all piston aircraft engines are approved for either 5/8 or 3/4 plugs.

Many customers call for information or clarification of documentation issues.

The applicability and approval documentation is the most frequent issue beyond the topics of mechanical troubleshooting. One of the grand paradoxes of the aviation industry is that the FAA demands that aircraft comply with the type certificate, but sometimes the information available in the Type Certificate Data Sheet does not reflect currently manufactured products.

There are some indirect sources of information that help with this scenario. Packaged with every magneto is a FAA approved application sheet that summarizes all of the FAA approved applications for Slick magnetos. Also, Slick Service Letter SL 1-89 provides the direct model supercedure for Slick magnetos. Lycoming provides excellent documents to support their TCDS. Lycoming Service Instruction 1443 lists all Lycoming engines and the applicable Slick magneto models.

Lycoming has recently updated many of their TCDS most of them refer back to S.I. 1443 for magneto applicability. If the TCM TCDS does not reflect a current magneto application, then Slick SL1-89 can be used to provide the Slick part number supercedure.

Slick Ignition Upgrade kits have been a popular retrofit to replace other ignition systems to avoid repetitive AD compliance. Refer to the application data sheet provided with the Slick magneto, the TCDS, or Lycoming S.I. 1443. In most cases Slick magnetos are a bolt-on replacement with no 337 or STC required.

However, some Slick applications are STC approved and do require that a 337 be filed to document the installation. For example, a common application that gets missed is the TCM O-300. The original Slick 664 can be found on the TCDS, and Slick SL1-89 lists the 6364 as a direct replacement for the 664. But the 6364 is approved via STC and needs a 337 to be completed to make the installation legal.

Unison Industries values feedback and encourages customers to contact the Slick Customer Service Department to obtain information on the products that they manufacture. For quick access to product support, contact the Unison industries/Slick Aircraft Products Customer Service Department in Rockford, Il; (815) 965-4700, ext. 143; Fax: 815-965-2457; E-mail:[email protected].