Unison magneto troubleshooting

Unison Magneto Troubleshooting By Harry Fenton February 1999 Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12...


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.

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