How to assess the condition of my stator

[JayCulpepper]

Hello to all, I have a 1978 Johnson 140 that I have recently purchased on a boat. I noticed the battery was not being charged because of a bad rectifier. This particular model does not have a regulator, so I installed a newer regulator/rectifier. Now I have good regulated voltage. I have never been able to get the tach to work and have read the stator could be the culprit. I have now decided to rebuild the motor and having removed the flywheel I see some black ooze coming from the stator. Not much, just a few splotches here and there. My question is: Did the bad rectifier cause heating to the stator and result in the black ooze? I know the voltage is being regulated and is charging my battery. I have tested the stator with an ohm meter and it reads .5 ohms across the yellow wires, and reads infinity from the yellow wire to the metal frame of the stator. As far as I can tell, from all the research I have done, the stator is acting and testing as a good one, except for the fact I have no tach. What are your thoughts on the condition of my stator? Was it just stressed or is it on it's last leg?
Thanks

 

[emdsapmgr]

Usually, if the stator is charging the system, then a tach signal should be produced. (You may want to try another tach.) It's from the charge coils, which are not the same as the coils that fire the ignition. Two different parts of the stator. You can get some great troubleshooting info on the ignition side from this website: cdielectronics.com. The original factory service manual has details on various tests for the charging system. The factory indicates that an ohm reading of 0.25
(+_ 0.1 ohm) between the two yellow stator wires is normal.

 

[gm280]

As emdsapmgr stated, if you are charging the battery without problems, then your stator and rectifier are both good. So there is no reason to replace them. The ignition system in your engine comes from separate coils for the ignition and nothing to do with the stator system at all... So focus your attention on the ignition coil and leave the stator alone... JMHO!

 

[scout-j-m]

I recently had a similar problem on my Force motor. My tach wasn't working nor was it charging the battery. Turns out my rectifier/regulator was bad as well as my stator's charging windings weren't outputting any AC voltage. I bought a new regulator/rectifier (cheap $40 off of eBay) and also a new CDI Electronics stator. Tested the stator charging windings and saw significant AC voltage and then I hooked it all up. Well the new rectifier/regulator was charging the battery but the tach was still not working. I unplugged the tach signal wire at the rectifier and did a continuity test from the motor up to where it attaches to the signal wire post on the tach. It did have continuity. I then tested the positive and negative leads on the tach and saw 12V across them with the ignition on. Now I knew it was either a bad tach or bad rectifier. I then jumped a connection from one of the yellow stator wires to the tach signal wire while it was running and.....bam, I had a working tach.

So it appears my rectifier/regulator is just not outputing correctly on the gray wire. This may be the same problem for you if you bought a cheap unit like I did. My work around is just going to be to make a small t-fitting out of wire and bullet connectors to connect in between my stator and rectifier and jump to my tach wire. Hope this helps.

 

[schematic]

As emdsapmgr stated, if you are charging the battery without problems, then your stator and rectifier are both good. So there is no reason to replace them. The ignition system in your engine comes from separate coils for the ignition and nothing to do with the stator system at all... So focus your attention on the ignition coil and leave the stator alone... JMHO!

A compromised charge coil can definitely affect the ignition system. A short within a coil can cause "high current/high magnet flux/heat" all which can hinder trigger and ignition charge coil function.

I have now decided to rebuild the motor and having removed the flywheel I see some black ooze coming from the stator. Not much, just a few splotches here and there. My question is: Did the bad rectifier cause heating to the stator and result in the black ooze? I know the voltage is being regulated and is charging my battery. What are your thoughts on the condition of my stator? Was it just stressed or is it on it's last leg?
Thanks

If you are a gambling man , reuse the overheated stator. If you are going through the trouble of an overhaul, why not replace a component giving you visual signs that it has been damaged. Weakened coil insulation can't heal itself, it can only get worse.
JMHO

 

[JayCulpepper]

The original factory service manual has details on various tests for the charging system. The factory indicates that an ohm reading of 0.25 (+_ 0.1 ohm) between the two yellow stator wires is normal.

My factory manual, specifically for my year engine, states a reading of 1.0 +/- 0.2 ohms for the 6amp stator and 0.5 +/- 0.2 ohms for the 10 amp stator. I have the 10 amp and I am reading exactly what the manual states as being good. If it was suppose to be 0.25 +/- 0.1 ohms and I was reading 0.5 it would have been out of spec and there would be no question about the condition of my stator. I appreciate your help.

 

[JayCulpepper]

The ignition system in your engine comes from separate coils for the ignition and nothing to do with the stator system at all... So focus your attention on the ignition coil and leave the stator alone... JMHO!

True the coils are separate, but are dependent on part of the windings in the stator for the pulses to initiate the spark for the engine to run. Thanks for your reply.

 

[JayCulpepper]

A compromised charge coil can definitely affect the ignition system. A short within a coil can cause "high current/high magnet flux/heat" all which can hinder trigger and ignition charge coil function.

I agree, I have checked the resistance to ground with an ohm meter and read infinity. I may try a megger at 500v and see if there is any indication of the break down of the insulation.

If you are a gambling man , reuse the overheated stator. If you are going through the trouble of an overhaul, why not replace a component giving you visual sines that it has been damaged. Weakened coil insulation can't heal itself, it can only get worse.

JMHO

I am a frugal man. Unlike a gambler, I like to base my actions on fact. I just do not have the experience with outboard components to make an educated assessment of the condition of the stator. I guess if the stator was not a $200+ item I would have just replaced it.
Thanks for your comments.

 

[JayCulpepper]

Hi guys, Having an awful time trying to pull the trigger on buying a new stator. It is hard for me to replace a working component. All the tests I know to do indicate a good stator. The running tests for the stator are good. I may have discovered the reason for no tach signal. I have the newer regulator/rectifier wires ( two yellows, red and gray)connected to the block at the locations of the old rectifier. The old rectifier did not have a gray. I laid the gray wire from the regulator/rectifier with the gray wire on the block. I did not realize there was a jumper between the yellow/gray and the gray terminals on the block. So I have been running with one of the yellow wires, in effect, shorted to the grey tach signal wire from the regulator/rectifier. Is it possible this may be the cause of my lack of a tach signal?

 

[schematic]

I agree, I have checked the resistance to ground with an ohm meter and read infinity. I may try a megger at 500v and see if there is any indication of the break down of the insulation.

A megger will prove unwanted paths to ground, but will not indicate shorts between windings. Dripping insulation is an indication of overheat. Without visually inspecting the windings, you are gambling.....Burnt bare windings may not show up with a resistance test but may "hug" when passing current due to the magnetic attraction resulting in internal shorts. Kinda like skin cancer.....small indicators on the outside can be the result of bad things on the inside.

I am a frugal man. Unlike a gambler, I like to base my actions on fact.

Me too. But sometimes its not possible to "prove" electrical damage without causing more....
If I was getting more than 15 VAC between the yellow stator wires while running, I would gamble cause I am cheap, and I do my boating just 100 yards outside my front lawn...LOL not far to row LOL

Is it possible this may be the cause of my lack of a tach signal?

Be sure you are getting more than 15 VAC between the yellow stator wires while running.
Simply connect the engine harness grey back to one of the stator yellow wires. Leave the reg/rec grey open for now. If the charging system functions and you have no tach readings, you have a bad tach or bad wiring to it.

 

[JayCulpepper]

A megger will prove unwanted paths to ground, but will not indicate shorts between windings. Dripping insulation is an indication of overheat. Without visually inspecting the windings, you are gambling.....Burnt bare windings may not show up with a resistance test but may "hug" when passing current due to the magnetic attraction resulting in internal shorts. Kinda like skin cancer.....small indicators on the outside can be the result of bad things on the inside.

I agree with that. In your opinion, if the insulation between the turns of some or all of the windings is degraded to the point of shorts, would those turn to turn shorts cause a decrease in voltage output?

Me too. But sometimes its not possible to "prove" electrical damage without causing more....
If I was getting more than 15 VAC between the yellow stator wires while running, I would gamble cause I am cheap, and I do my boating just 100 yards outside my front lawn...LOL not far to row LOL.

I am considering the initial heating to be caused by the rectifier failure and now since that repair I have not had any charging or ignition problems. I was getting about 14.5 volts regulated dc when you first crank up and then tapers down to about 13 vdc.

Be sure you are getting more than 15 VAC between the yellow stator wires while running.
Simply connect the engine harness grey back to one of the stator yellow wires. Leave the reg/rec grey open for now. If the charging system functions and you have no tach readings, you have a bad tach or bad wiring to it.

I have the block at the machine shop now, but when I first installed the regulator/rectifier, I did not have the gray wire from the regulator/rectifier connected to anything and one of the yellows were connected to the engine harness gray through the jumper that was on the terminal block. This was just like the original rectifier was connected. At that time I had no tach signal. The part I have installed is an integrated regulator/rectifier. Sould a tach signal be on the yellow from the stator and on the gray from the regulator/rectifier? :crazy: Why, yeesss.:triumphant: Oh well, I guess I still have to determine if I have a bad tach.:help: I guess I thought that changing the tach signal from directly connected to the yellow stator wire to the gray wire from the rectifier/regulator was going to miraculously make my tach start working. I guess, once I get the motor running, I will do some more testing related to the stator and tach signal. I need to do some more research on that tach signal so I will know what to look for when testing. I just hope I don't need an oscilloscope to see the pulses. I am going to guess a tach will be in order.
Thanks for your direction.

 

[schematic]

I agree with that. In your opinion, if the insulation between the turns of some or all of the windings is degraded to the point of shorts, would those turn to turn shorts cause a decrease in voltage output?

Shorted windings will decrease output voltage. The problem is.... output from stators can reach 40+ volts. Missing a few volts from shorts can be undetectable since we have more than what we need. If shorts are present, overheating of the stator can occur...The shorted windings become heating elements.

Sould a tach signal be on the yellow from the stator and on the gray from the regulator/rectifier?

Either one, or the other, but not both. Some tachs can be a little fussy on which signal they prefer. Having the tach connected to the Rec/Reg is preferred, as it can give an indication of charging system failure (no tach operation) if the charging system quits.