1974 Mercury 850 serial#4123383 / bad stator

Doc279

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I recently picked up this 1974 Mercury 850.
The wiring is toast and has rotted away. I removed all of the old wiring and used new wire to connect everything on the engine.

With 12 volts (battery) connected - I have spark on all 4 cylinders. The stator is not putting out anything. My question is- will this motor run with 12 volt battery power connected to the switch box only? I really do not want to spend the $300.00 on a new stator. The stator is the two wire style that goes to the rectiifier and then a single wire runs from the rectifier to the #3 post on the switch box.

I tried to repair the stator wiring but the bakelite coating prevented me from making a good connection. Any tips on removing the bakelite?

It is winter time and I am trying to make this old motor live again. Quality garage time near the wood stove!
 

Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Additionally, all 4 cylinders show 150 lbs. on the compression test. The motor spins over well with the electric starter and the distributor cap and rotor have been cleaned up with a dremel tool and small wire brush. I believe that this engine will run! The question is - will the battery 12 volt be enough to allow this engine to run without any help from the two wire stator?

Thanks in advance for any answers or questions.
 

Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Surely somebody has an opinion? I've cleaned the carbs and installed new gaskets - lower unit has new water pump impeller and gear lube now. I hope to try and start it by tomorrow afternoon?

The wiring diagram shows that the #3 post on the switch box has a constant hot from the battery and the wire from the rectifier joins on the same post (I believe this to be a way to charge the battery from the stator) As long as the #4 post on the switch box (white wire) has switched 12 volts - I have spark from the distributor and coil to the spark plugs. I am learning as I continue to work my way through this.
 

Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

I guess that I will not get any opinions? 58 views and 1 response - for selling a part. I may try and start this motor later today - heavy rain and cold here today. Thank god for the garage!!!!

Happy New Year ALL! We SURE need a better one than 2013
 

sam am I

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Lol....the passive aggressive approach worked, this time!!...........Yes, it will run BUT, It will die in time obviously. Just how long? Not sure, depends on how much energy the motor's electronic/electrical systems use and the capacity/condition of your batt/s. It will be like running a car that the alt is not working I suppose.

The one thing I'm not sure about is, is that stator tapped off of in any way as to use the AC side as a signal into system switching, positioning, tech'ing etc. I'm not too familiar with that engine BUT, if the stator is used solely for charging(which appears to be the case after reviewing the schematic) , yes, it will run for a while till the batt. drops down too low.

http://www.maxrules.com/oldmercs/Wiring/1966ona/30.pdf
 
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Chris1956

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Re: 1974 Mercury 850 serial#4123383 / bad stator

You have tested the stator with an ohmmeter? The only continuity is from wire to wire. The stator is not grounded. Make sure you remove the rectifier from the circuit and test only the stator across the two leads. I have not seen that kind of a stator go bad, but it likely happens.
 

sandhopper2

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Re: 1974 Mercury 850 serial#4123383 / bad stator

I have the same Stator , wires were bare of the insulation I connected 2 new yellow wires and shrink wrap as close as I could
What reading should I get on the Ohm meter ?
The rest of the wiring is just as bad so I hope this way will work the cost of new harness is crazy for a few wires (6)
Larry
 

Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Thanks SAM am I - yes that is the exact schematic that I have. If this motor runs well enough I will mount it on my 24' pontoon boat.
I have a smart charger that I will keep the battery charge with. I have three batteries on this boat all with 1000cca. The boat is used on a lake and we will never be to far from the dock. We fish and swim off of the pontoon boat with all my grandchildren. If I have to swap out the engine battery because the engine dies - no big deal.

Chris1956 - I checked the stator and it shows continuity between the wires - when disconnected from the rectifier. When the wires are connected to the rectifier - they show continuity to ground. Disconnected from the rectifier - they do not?

I checked the wires disconnected from the rectifier when I was cranking the engine - no voltage of any kind was shown on my analog meter. I will check again using my Fluke digital meter later today. The original stator wires were rotten all the way to the bakelite coating. I ground them back to just copper dots with a dremel tool - then drilled small holes in the center of the copper dots. I then took 16ga wire and stripped the ends and soldered them as best I could. I used JB weld to anchor the wires from there to the bottom of the stator bakelite. Obviously, I was hoping for a better outcome!

Sorry for the passive aggressive approach - but it worked this time! LOL

I have several of these old motors - my 1974 Mercury 650 has the lightning energizer distributor - runs like a top. I also own a couple of the Mercury 500 that I have been tinkering with. These old motors are cheap to play with while learning about the old technology.

Posting in here is just me thinking out loud as I work through some of this. I like different opinions and maybe I will glean an answer from some of the discussions? Thanks for participating! LOL
 

Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Sandhopper2 - according to what I can find - you should see 56-76 ohms between the stator wires - they should not show anything when checked to ground (infinity) The chart shows 180 volts A/C when cranking between the disconnected wires from the stator.
The chart also shows 20 volts D/C from the single wire on the rectifier lead.

This what I am attempting to use?
 

Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

No voltage from my stator using the Fluke digital meter. No chance to see if it will run - the grand kids invaded my garage. We spent the afternoon playing with trucks and wood blocks on the floor while it rained outside. Good quality fun for a 6 year old, 5 year old and a 55 year old kid! They had a blast!
 

sandhopper2

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Doc279
Thanks for the numbers , mine shows 0 so maybe my scale is wrong or mine is bad also
As I understand the stator is for charging the battery right ?
so after I get this thing to reun then maybe look at stator again
Larry
 

Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Yes the stator on these motors are for charging the battery only. The engine will run with just battery power connected to the switch box.
Red is constant hot and the white post is for switched hot from the key switch.

I will address my stator issue at a later date - maybe? if it is an issue. I carry several batteries on my pontoon boat - I troll and fish quite a bit with it. My outboard engine is for crossing the lake or going from one cove to another.
 

Chris1956

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Doc, It sounds like your rectifier is bad. That frequently happens. When the rectifier is bad you will not get any charging or tach signal. It may also drain the battery.
 

sam am I

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Re: 1974 Mercury 850 serial#4123383 / bad stator

I think he confirmed the stator was dead Chris......The Stator sounds shorted because I think he went as far as he was just looking for AC with the rectifier even removed from the circuit. Rectifier could be bad as well though

I checked the wires disconnected from the rectifier when I was cranking the engine - no voltage of any kind was shown on my analog meter.I will check again using my Fluke digital meter later today.

No voltage from my stator using the Fluke digital meter.
 
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Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Yep - I get nothing from the stator wires while cranking the engine. They were disconnected from the rectifier.
The ohm test between the wires is good though???? I was hoping for better results. No chance today to see if the engine would run - duty called elsewhere. Maybe tomorrow?

I received the great news that I will be laid off with no paycheck for the month of January - no warning at all - thanks boss! CHIT
 

sam am I

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Re: 1974 Mercury 850 serial#4123383 / bad stator

I'm not sure, was the resistance you measured the same'ish as what the book says it should have been?

If its close, then it's not shorted or open.....hmmm, magnets okay under the flywheel?

What model number fluke are you using?

Maybe there is AC there but it's too fast for your meter. Cranking is pretty slow though still

With no batt attached the rectifier's "pos" output will be unfiltered DC (Pulsed DC/magnetic pole...sorta AC still)

Might end up making a DVA to capture a peak of what might be there

DVA.jpg


Bummer about work dude
 
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Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Sam the ohms read right at 75 between the wires. My fluke is a model 98 if memory serves me right.
I will do nothing else until I get the motor running - maybe it will kick in and work? Neither of the stator wires showed any continuity to ground. I just read a rectifier check in my old manual - I will check it in the morning.

Work has been kind of slow all year. I am a marine surveyor for a company located in Chicago. I spent 24 years working for Sea Ray and stepped away to become a surveyor. I love the job but it is kind of storm related as we do a LOT of insurance work. The storms just never really happened this year. We finished up in New Jersey and New York in late spring from Sandy. Unemployment in the state of Tennessee is minimal at best.
 

sam am I

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Hmmmm, well the bandwidth on a fluke 9x series should be fast enough, 100kHz I think.

I'm baffled as to why no, zip, zero AC with all the winding's there (75Ω) on a unloaded stator and a meter fast enough (6MRPM probably or more) to see something cranking on a starter.........K sry, I have to ask, you had the meter set to "AC" right?
 
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Doc279

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Re: 1974 Mercury 850 serial#4123383 / bad stator

Oh yes sir I did! LOL I had a hot battery and also checked it with the spark plugs out (faster rpm)
I looked at the flywheel magnets when I had it off - nothing unusual - I did hit them with some 220 grit sand paper just to clean them up.

I will check the rectifier in the morning but with nothing on the stator wires while disconnected - it is a mute point.
 
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