Mercury 650 charging problem

[650thunder]

Hi all and hope all is well,

I have a 1971 mercury 650 4 cylinder (ser number starts with 300) which starts and runs like a dream every time but on our last outing the battery went flat and wouldnt turn the motor over.
So got her going with the emergency pull rope first pull mind you! Was well pleased with that ! When she fired i noticed the fuel fump leaking all over a sealed black module directly below it. The two wires from the stator /alternator under the flywheel run to it and another red wire runs away to the front of the engine i assume eventually to the battery.

Got a gasket set for the fuel pump but seems to be the wrong one.It doesnt seem to seal the top corner of the upper chamber of the pump. Will have to look into that.

Battery is new and marine style shows 12.4 volts on multi meter

Can anyone outline some troubleshooting test i can perform to determine the problem like resitance test and values and voltage test when running and at which points to test from.

Any and all advice appreciated

Regards Tony

 

[Laddies]

Re: Mercury 650 charging problem

The simplist test is hook a voltmeter to the battery, start the engine and run it in down the lake at 3500+ RPMs and you should see a voltage rise. To test the system with a OHM meter and the stator wires disconnected from the rectifier you should get a reading od .5 to .7 OHMs, really any continuity yellow to yellow will work and 0 yellow to ground. Here's the rectifier test.

 

[650thunder]

Re: Mercury 650 charging problem

Thanks for the rectifier test sheet will get on to it first thing tomorrow will let you know how it goes. thanks again
regards Tony

 

[650thunder]

Re: Mercury 650 charging problem

yes the rectifier tests failed will try to source another thanks again

 

[Chris1956]

Re: Mercury 650 charging problem

Merc superceeded the ugly old rectifier you have with a 1.5" X 1.5" three pole black rectifier. it is meant to bolt to the front cowling support, under the switchbox.

You may also use a $5, 25Amp full wave Bridge rectifer from Radio shack. Be sure to ground the -DC connector and change the ring connectors you have to spade connectors, if you go that route. The two yellow stator wires connect to the two AC connectors on the rectifier. Red battery wire goes to the +DC connector.

 

[Laddies]

Re: Mercury 650 charging problem

Chris, I see you recommend this Radio Shack rectifier many times, almost everyone knows that rectifiers are are interchangeable as long as the are rated for the amps that the alternator puts out but we were always told that one should always use Coast Guard rate marine parts so I have always refrained from recommending using those type of things to others. So imagine my surprise to read this post of yours.

#2 January 23rd, 2009, 08:41 AM
Chris1956
Vice Admiral
Join Date: Mar 2004
Posts: 5,660

Re: Marine parts VS Automobile parts !

--------------------------------------------------------------------------------

The Chief is correct about the importance of using Marine-rated parts for electrical and fuel components. Insurance claims aside, marine-rated parts help prevent fires, explosions and the injuries that come with them.

There are a lot of non-marine parts that are common between automobiles and sterndrive motors. Some of these are fan belts, bearings, oil pans and timing covers, valve covers, intake manifolds, spark plugs and internal engine components (valves, rods, cranks, pistons) etc.

Just wonder which way it is?

 

[Chris1956]

Re: Mercury 650 charging problem

Ladies, A rectifier is a solid state part. They can not spark since they are encased in a plastic potting material. I suppose if a wire came loose, they could spark, but that would be inherent to any component, or any grounded part a "live" wire might touch. The charging system on that motor also does not create enough current to melt any of the wires, should the rectifier short, which the OEM rectifiers do as well.

In addition, outboard powerheads are not subject to the same regulations that inboard bilges are, since fuel can run into the water, and they are passively ventilated. I have never seen a powered blower on an OB.

 

[Laddies]

Re: Mercury 650 charging problem

Chris, The Radio Shack wave bridge rectifier does omit extra heat and even though you are not required a blower under a outboard cowl the engines fuel system and electrical parts still have Coast Guard requirements to meet. I believe you were the one that brought this up, "Insurance claims aside, marine-rated parts help prevent fires, explosions and the injuries that come with them."
Wasn't that you Chris.

 

[Chris1956]

Re: Mercury 650 charging problem

Laddies, Those were my words, when discussing sterndrive issues. If you look in the USCG Basic Seamanship manual they discuss requirements for engines in boats that were "decked over after July 1940". This is the origin of the requirement for a spark arrestor on an inboard. The same regulation specifically excludes the need for spark arrestors on outboard motors. these regulations have been updated over the years to include sterndrive boats, which wern't invented in 1940. However, I would bet Outboard engines have different regulations, than inboard or sterndrive boats. I have also never seen an SAE marking on an outboard rectifier.

Mostly our arguement is mute since most parts one would use on an outboard, are specifically made for an outboard. This makes it difficult to install non recommended parts. i.e. I have never seen a starter or alternator that would fit an outboard, other than the ones specifically made for an outboard. I would also recommend marine rated fuel lines for obvious reasons.

BTW - Why would a RS Rectifier produce more heat than an OEM Rectifier?

 

[Laddies]

Re: Mercury 650 charging problem

Chris, many years ago the Mercury outboards with selenium rectifiers did have a Coast Guard approval on them and when they became NLA the service bulletin on the kit to convert to a diode rectifier gave a Coast Guard approval number on it. When giving advice I try to opt on the side of safety when i give my opinion, you certainly have a right to you so give what ever advice that you chose thats what forums are for. If you doubt that a wave bridge or selenium rectifier don't get hot touch one, I would recommend that you touch a diode rectifier first so that your fingers are not burned in the first encounter. Anyway this is a waste of our time I for one done with it.