Repeat Stator Failure? Bigger problem?

Hi All,
Thanks for all the great advice over the past couple years. It's helped me keep a couple engines afloat when they maybe shouldn't have.
I'm working with a 78 Johnson 115HP. It had been used very sparingly in its first couple of years, then garage stored literally for 30 years. We got it out last summer and got it going without much fuss.
I have, for the second time in three trips out, been left in the middle of the bay due to a bad stator. Each time it happened, it was very sudden. I had been stopped for about 20 minutes and when I tried to crank the engine, no such luck. Each time now, I have checked the resistance to the stator and it rang up between 425-600 Ohms with no spark from any cylinder. The first time, I replaced it with a used stator from a working engine and things fired right up. Now, I've burned out a second and I'm wondering what the heck is happening. I hesitate to find another because I'm afraid there's a bigger problem causing the stator to fail.
Can anyone give me a lead as to what to start checking?
Is it possible I'm just that unlucky?

Thanks,

Re: Repeat Stator Failure? Bigger problem?

I think what you need is an OEM factory service manual and a peak reading voltmeter to check the outputs of the ignition system. I have a later service manual and your ohm readings aren't to far off.

Re: Repeat Stator Failure? Bigger problem?

Ditto on the service book, it will pay for itself immediately.
www.outboardbooks.com

Re: Repeat Stator Failure? Bigger problem?

In order to determine whether something acting on the stator caused it to fail, you need to know what actually failed in the stator. Is the damage external or internal? Regardless, if you need to replace it I would get a new OEM or a Rapair unit.

Re: Repeat Stator Failure? Bigger problem?

The 1978 V4 OMC engines incorporate a small three (3) wire rectifier. If this rectifier is damaged (shorted etc), the AC voltage/current generated within that stator when running cannot be converted to DC voltage and pass thru the rectifier in order to charge the battery. Hence that AC voltage will simply sit there under the flywheel and cause the stator to melt down. Check that rectifier as follows.

(Small Rectifier Description & Location)
(J. Reeves)

On most 2,3,4,6 cylinder engines, the small rectifier is located on the starboard (right) side of the engine just in front of the engines electrical wiring strip. There are a few older V4 engines that have the wiring strip on the rear portion of the engine and the rectifier would be located just under that terminal strip. The smaller horsepower engines usually have the rectifier located on the starboard side of the powerhead close to the carburetor area.

The rectifier appears to be a round object approximately one inch (1") in diameter and also about one inch (1") high. The base of it is sort of triangular in appearance and is attached to the engine with two (2) screws/bolts..... usually one screw/bolt is larger than the other. The rectifier, depending on which one your engine uses, will have either:

One Red wire, one Yellow wire, and one Yellow/Gray wire, or One Red wire, and two Yellow wires.

Note that either of the above rectifiers could have a fourth wire which would be Yellow/Blue

********************
(Small Rectifier Test)
(J. Reeves)

Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.

Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.

Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.

Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.

*****************

Possibly the stator and rectifier are okay..... and your problem lies elsewhere? Read on......

(Standard Spark Test)
(J.Reeves)

Remove the spark plugs so that the engine can turn over as fast as possible at cranking speed. The ignition is self contained (not dependent on battery voltage) and the engine must turn over at least 300 rpm in order for the stator under the flywheel to generate the needed 300v AC which must be delivered to the powerpack.

Rig up some kind of a spark tester whereas you can set a 7/16" gap for the spark to jump. You can design a multi spark tester of simply move the tester from one plug wire to the other.

Crank the engine and observe the spark. The spark should jump that 7/16" gap with a strong blue lightning like flame..... a real strong blue snap!

If no spark, or if the spark is weak, disconnect the main RED electrical connector at the engine. Now using a small jumper from the battery terminal of the starter solenoid to the 3/8" nut terminal of the solenoid that engages the solenoid (not the 3/8" ground nut), crank the engine again and observe the spark.

If you now have spark, the usual problem is that a short exists in the ignition switch, in which case replace the switch. If still no spark (assuming the stator is okay), it's usually a case that the engine is cranking too slow.

Re: Repeat Stator Failure? Bigger problem?

very thorough answer there Joe...should make that a sticky

Re: Repeat Stator Failure? Bigger problem?

Sparkie..... All except the first paragraph is probably in there already.