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Author Topic:   Mercury Stator Failure
GAwhale posted 06-13-2008 10:05 PM ET (US)   Profile for GAwhale   Send Email to GAwhale  
The stator on my 2001 Mercury 90 two-cycle failed in the middle of nowhere. What causes the stator to go bad?

Should it be an item to change out after a certain time period?

I paid a mobile marine mechanic $150 just to diagnose the problem in Beaufort, SC. He was unable to get the part on a Sunday.

I picked up my boat from the shop today: Red (whatever that means) Stator cost $217.82 and 1.5 hours labor ($97.50).

jimh posted 06-13-2008 10:37 PM ET (US)     Profile for jimh  Send Email to jimh     
A stator is nothing more than a long length of copper wire wound around some magnet poles, and it has no moving parts. You would think it would last a lifetime. What failed on your stator? (My guess is that) most likely the insulation on the wiring failed and a short circuit developed. A short to the engine block will cause a big problem for a stator. Turns that short together will also cause problems.

Most stators are wound with a copper wire that has enamel or Formvar resin as an insulating coating. The enemy of these materials is heat, as when they are heated they tend to melt. A stator is located on the top of the engine, and, since heat rises, the top of the engine tends to be a hot spot. Some engine manufacturers (like Bombardier notably) incorporate fan blades into the flywheel (which rotates above the stator) so that cooling air is drawn into the area and heat is dissipated.

The wiring of the stator could also become damaged by contact with the flywheel if the wiring became hot and sagged. The stator wires can also be damaged if excess current is flowing, such as could occur with a short circuit in the charging circuit, or from a failure of the regulator or rectifier.

Mercury stators seem to be identified by a color coding which apparently differentiates models or epochs of stators or replacement parts. Perhaps a Mercury expert can tell of the significance of the red stator part.

Replacement of the stator requires removal of the flywheel, but otherwise it is not particularly onerous to service. Here is a picture of a stator: stator725x518.jpg

The term "stator" is also often applied to the entire assembly of coils under the flywheel if there is one unitized part. So the "stator" could include several coil assemblies, and among them would be the battery charger alternator stator, the capacitor discharge ignition alternator stator, and the spark timing coils. An assembly with all of these can be expensive. Some manufacturers separate the coil assemblies into individual parts, and this makes replacement less expensive if only one coil assembly is needed.

jimh posted 06-13-2008 10:45 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is a picture of a flywheel which has fan blades in order to help move air through the area of the stator: jpg
Shown is an E-TEC 115-HP motor

jimh posted 06-13-2008 10:52 PM ET (US)     Profile for jimh  Send Email to jimh     
If the stator assembly contains the ignition timing coils, the usual recommendation after replacement of the stators is for the engine timing to be checked and reset. Ask your mechanic if he performed a complete engine ignition timing check. In order to do this he would have to first verify the accuracy of the timing mark using a piston top travel indicator, then he would have to connect a timing light and run the engine throughout its rated speed range. This usually requires replacing the propeller with a test propeller and running the engine in a large test tank so that the engine can be operated at high speeds (in the range of 4,000-RPM or more) in order that the ignition timing and spark advance is verified at higher throttle settings. (The spark timing advances with throttle setting.)
GAwhale posted 06-14-2008 09:39 AM ET (US)     Profile for GAwhale  Send Email to GAwhale     
Hi Jim,

Thank you for all the good information. It was a hot day when my engine failed. We had stopped for lunch. The engine was in the up position since we were anchored very close to the shore. Often when I put my engine up, the carbs flood and she is hard to start. I thought this was the problem.

I have been very pleased with the service and price at Mitchell Marine . They are a family owned business. They have a mechanic named Wally who is truly a redneck, but knows his stuff. I do not know if they checked the timing, but my engine did seem to start a little better and ran great all afternoon on the lake Friday when I picked up my Montauk.

Jefecinco posted 06-14-2008 09:42 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Many years ago (20+) when writing the purchase specifications for some AC generator sets we required stators to be epoxy "VPI" to make them less vulnerable to failure due to rough handling and very hot operating conditions. I believe the VPI stood for "vacuum-pressure-impregnation" or some such.

As it turned out none of the stators purchased ever failed. If Mercury Marine is concerned about their stator failure rates they should consider "VPI" or cooling fins. Of course they would sell far fewer stators if they improved them.


GAwhale posted 06-16-2008 11:12 AM ET (US)     Profile for GAwhale  Send Email to GAwhale     
I'm still trying to understand the basics.

Does every outboard engine have a stator ? (I have an old technology two stroke, how about the modern four strokes?)

Would the comparable part on an automobile be the alternator?

jimh posted 06-16-2008 01:34 PM ET (US)     Profile for jimh  Send Email to jimh     
You ought to read my article in the REFERENCE section on how outboard motors generate electrical power

Boat Electrical Power Generation
by James W. Hebert

It will explain how outboard motors generate electricity.

Two-stroke motors have alternators. Two-stroke motors usually use a permanent magnet alternator, which is a very efficient alternator. Automobiles are beginning to return to permanent magnet alternators as their power requirements rise. You can read about permanent magnet alternators in the REFERENCE section:

Permanent Magnet Alternators
by James W. Hebert

The only reason stators fail is poor design, poor construction, poor quality, of from failures caused by associated devices (also of poor design, poor construction, and poor quality). There is no inherent reason why a stator ought to just wear out.

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