Questions and Answers 4

Electrical

Q....................... My plane has the original 377. There are several wires coming from the engine, with several types of connectors. What do they all do ?

A........................ There are differing numbers of wires so I'll start with the point engines.
Pint engines can be identified by the two separate coils with one wire from each coil going to each of the cylinders. This engine has three coils inside the flywheel, this comprising what some may call a magneto.
The two green wires are the low poer lighting coil. The two yellow are the higher power lighting coil. The two black wires are the two kill switch wires and they are connected together to shut off the engine. In doing so, they short the third coil that runs the ignition. There is also a brown wire, and this wire is merely a ground with no specific use in either the lighting coils or the kill switch wires. I remove it from engines while doing service work on them.

Q......................... My plane has a Cuyuna 430 with the same color wires. Are they the same ?

A......................... Both engines using points have identical wiring, at least externally. The 430 has condensors with soldered wires connecting it to the points and the ignition coil. Early Rotax engines were the same, then went to a Rotax specific set of points and condensors where the wires attach to the condensor with a small nut and stud sticking out of the condensor. The points rather than having a small nut/bolt attaching the wires, has the wire permantently attached, again making the points Rotax specific.
Rotax specific means higher costs for the most part.

Q......................... I have a tach and it reads erratically. Do I ned a new one ?

A......................... Before buying a new one, i would surely check, maybe disconect and reconnect, all the wires from the coil to the tach.
Loose or corroded connections may be much of the tach problems out there. You can also check the tach by trying it on another engine, using a couple long pieces of jumper wire.

Q......................... How big of a wire does a tach need ?

A......................... Since the tach pulls absolutely no current to speak of, even very small phone wire may be used.

Q........................ How long of an extension can I use for gauges ?

A........................ I have extended wires up to 14 feet on the GT 400 with the engine mounted far back, the dash pretty far forward. The tach uses plses and even small wire may be used. The non powered gauges such as CHT and EGT, use a voltage generated by the probe. This means that if the wire is really small, voltage drops can reduce the reading at the gauge. I recommened using number 18 wire for anything over 6 feet.

Q....................... My gauges have smal pins on the back. What do I use to connect the wires ?

A....................... I purchased a kit made by Molex. It comes with various pins, connectors and a special set of crimping pliers.
The pin diameters are .090 inches so if you buy one, get this size as they make several. This would allow making brand new wires from the sending unit to the gauge. Choosing various colors of wire woul also help when connecting the wires at the gauge.
If you only need a couple wire extended, cut the wire a short distance from the female pin, and do a neat splice using solder and heatshrink. By this method, the ends are the original ones, with 18 gauge wire between.

Q....................... I have a tiny tach and it seems to read way off from what the engine is doing. Are they adjustable ?

A........................ Maybe at the factory, there is a way to calibrate them. But the tiny tach comes in many variations to adapt it to the many types of igniton and coil systems found on our engines.
When ordering any tach, make sure you know which type of ignition you have. The magneto puts out differeing numbers of pulses, and this is counted by the tach to establish the RPM. Trying a Ducati CDI tach on a points engine will read low by a fcator of three. To run a points tach on the Ducati would read three times too high.

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