Yanmar 1gm10 alternator wiring question

[johnlikesail]

All,

I am the proud new owner of a Japanese-made Yanmar 1gm10 from the early 90s.

I am running through everything and replacing all worn parts (thermo, zinc, alt belt, water pump, etc).

I just noticed yesterday that the battery terminal (it is clearly marked) on the back of the alternator has a bare wire sticking out, in addition to what looks like the main wire. I am a total newbie at this, but my guess is that someone had installed a water heater or some type of component that has since been taken out. However, I am worried because the red wire was just sticking straight up totally bare (in the pictures I have already capped it off).

I plan on running the motor this weekend to see if alt is functioning, bare wire has power through it, etc.

Anyone super-familiar with this motor have any thoughts or advice for me on this? It would be MUCH appreciated. Thanks for your time.

[four winds]

Same alt as mine. I think your assumption is correct.

Consider simply removing the extra wire. The big charge wire likely goes to the battery selector switch. So turn it to off, or remove the battery cable and it's simple to remove the nut on the alternator to remove the extra wire.

Also a good chance to assure the stud is secure in the alt frame.

Take care not to turn the stud when reinstalling the charge wire.


Welcome to the forum.

[johnlikesail]

Thanks four winds for your reply!

What about the black ground wire? You can see in the picture it is bolted onto the back of the alt to a different location, but then also just bare sticking straight up. Should I remove that as well?

Thanks a ton!!!

[four winds]

Well, that one is a mystery to me. That stud is unused on my alternator. And also is not shown on my wiring diagram in the manual.

Can't quickly inpect mine, but I think that stud is not insulated from the case and would be a case ground. Which is not needed since the case grounds through the mount.

I suspect this wire was used as a convenient ground for whatever the extra red wire was for.

[tinkrman69]

Originally Posted by four winds

Well, that one is a mystery to me. That stud is unused on my alternator. And also is not shown on my wiring diagram in the manual.

Can't quickly inpect mine, but I think that stud is not insulated from the case and would be a case ground. Which is not needed since the case grounds through the mount.

I suspect this wire was used as a convenient ground for whatever the extra red wire was for.

my YWM8 had the same alternator and I agree with Fourwinds on this. remove the wires going nowhere and you can leave the extra ground if you like as it will only endure a good ground to the system. some times the ground through the engine.....having many connection points....isn't all that good with age. the more connections you have in a circuit the more amps it consumes.

[Chuck Hawley]

I think the red wire may have been run to a second battery or some sort of parallel charge device. I agree that you should just remove it. However, the heavy output wire (red) probably goes to the starter solenoid, not the battery selector switch. Same idea, since the starter solenoid will have a large positive wire (presumably red) that goes to the common terminal of the battery switch.

The black wire is actually a pretty good idea. Most alternators are grounded through their cases to the engine block but over time there can be resistance due to rust or inadequate clamping force on the bracket. Having a ground wire from the alternator frame to the negative terminal on the engine (in my case, back of the engine near the transmission) isn't a bad idea. It should be sized the same as the output wire.

Cheers,

Chuck

[Compass790]

Just another thought for you. If you have the same type of trochoidal oil pump as the YSM8 Yanmar ( 1gm10 predecessor ) with a triangular cover held on by 3 bolts put an oil pressure gauge on it where the oil pressure sender fits & check the oil pressure. You have to get the engine hot to get an accurate reading, I'd say at least 20 mins under load.Our engines oil pressure is 40psi when cold & less than 20 psi when hot. ( Crank & bearings both severely worn, should be 35-50 psi) If the oil pressure is too low you have 2 probable causes, either the bearings are worn or the oil pump is worn. Most people just buy a new rotor assembly but the problem more commonly is the rotor chews it's way down into the case over time resulting in too great a clearance between the bolt on cover and the rotor. A new rotor assembly wont fix this. Yanmar will sell you a new engine case for a kings ransom but you can just file it down where the cover sits or have it milled if you are fussy to get the clearance within spec.
My oil pressure alarm went off occaisionally & 2 mechanics told me to put an oil pressure guage on it & if the oil pressure is ok just disconnect the sender. ( BIG MISTAKE) They neglected to tell me the engine had to be HOT but I should have known. Now I have both the sender alarm & an oil pressure guage running off a tee. Just trying to save you some grief. Can pm me if you have any questions

[billgewater]

I have had my Yanmar 1 GM from about 1985. Purchased at a bargain price (new) of $1400 AUD in Darwin when a business was closing down. I sold the Kanzaki gearbox for $1800 and then bolted a lay shaft onto the flywheel. The shaft ran a freezer compressor, an A/C compressor, a diving compressor and a water pump.(all with clutches except for the water pump) I also attached an extra pulley to the front and then hung a 5.5KVA 240 VAC alternator underneath. No, I did not run all at the same time! This little engine was going to earn its keep.
The small built in water pump was “removed” as the impellers didn’t last for long and were expensive. The 1 inch pump provided the raw water cooling for both the engine and the condensers for the freezer and A/C.
Being a propulsion engine, the voltage regulation for the alternator is nonexistent. The alternator runs electric jugs, power tools etc. Manual (throttle) regulation is required to run a microwave oven. I could not locate a “bolt on” regulator.
This has been in place since installation. For ten years it was run for about 8 hours every day. Since then, the yacht has been in marinas so little use was required.
The big grace with this engine is that being direct salt water cooled, it does not require a heat exchanger.
My engine has shown no corrosion problems in the casting or cooling gallery of the head.
Issues. Maintain it carefully. Oil, filters air cleaner and the zinc electrode. (buy all in bulk but not from Yanmar.. too expensive). Use a quality primary filter and preferably an overhead fuel tank. Fuel bleeding is a pain as it must be done at every fitting. I have installed a bleeder fitting on the top of the secondary (small) filter. (It is a refrigeration type bleeder. Cheap)
The alternator is a Mitsubishi model. You may consider replacing it with a larger one if space is available. The starter motor is also available from other suppliers. I have replaced both recently.
An issue here is: - the B+ terminal is the regulated output. It should be connected back into regulator with a short wire. Removal causes the output to lift from 14.26 Volts to 15.24 Volts which is too high. If not sure, ask someone who does.
The original lift pump can have a short life with the little valves failing. Try to keep a spare, or parts.
However, the worst problem was the copper exhaust manifold. It will corrode inside (not observable) and then leave salt spray on the very small exhaust hole on the head. This will ultimately shrink the exhaust hole and corrode the head. Due to the internal copper bent pipe, repairing the exhaust is very difficult.
The Yanmar exhaust replacement price will shock you so do consider having a SS one made from off the shelf parts (threaded). Also, the exhaust has three mounting studs. If possible, tap a fourth threaded hole into the head and use a more substantive four hole exhaust manifold flange. The copper one distorts too easily and can leak.
Some other owners have mentioned corrosion of an oil line that passes under the engine. Keep an eye on it!
The key switch on the panel is given to breaking where it goes through the panel. Look out for a more robust alternative. I have repaired mine a few times with super glue.
I have also added a manual valve and drain hose at the sump to allow for complete oil draining as the plug is not easily accessible for my installation.
I made my own exhaust muffler using 150 mm PVC vertical pipe 60 cm high. The wet exhaust enters via a flexible rubber exhaust hose at the top and goes down an internal 50 mm perforated pipe. The outlet is at the top and consists of a 50 mm internal pipe that reaches down to about 10 cm off the bottom. The hull outlet is over a meter above the load water line at the transom, thus reducing heeling issues (water ingress). The cylinder base also has a drain with a manual valve. All plastic. Clearly there are variations of this mode, but it has the important “non return” effect. You can hardly hear the engine running.
I have had no experience with the oil pump issue mentioned. Maybe I am due for it!
Being a single cylinder engine it can leap around a bit. Flexible mounts are essential. Over all though, a good little engine that keeps on working. Just avoid anything with a Yanmar sticker on it.

[GordMay]

Greetings and welcome aboard the CF, John.

[johnlikesail]

I was doing some other work on the engine and I put a voltimeter to the bare red wire in question while the motor was running and while the motor was off. I got a reading of 12 Volts alt current and 8.1 volts direct current...it was the same whether the motor was on or off, which tells me I was just measuring the battery. The "charge" light on my instrument panel (where the key goes) stayed on the entire 20 minute period I was running the engine. This tells me something is definitely wrong?

I have the exhaust manifold off now and other projects (rebuilding seawater strainer as well)...so I will have to wait a week or two and then I read online I should run the battery and measure at the battery itself...should be above 12 volts if batteries are charged and alternator is working...

I wonder if my alternator is working at all...

[four winds]

Measure the voltage at the battery terminals for reference.

8.1v isn't enough to turn over the engine to start it. Having that voyage at the alternator suggests there is a connection or corrosion problem somewhere between the battery and the alternator connection.

Your alternator may not be working, but, you need to be able to see almost the same voltage at the battery and alt connection before any conclusions about alt performance are really possible.

Chuck, yes of course the charge wire goes to the starter, then the starter cable to the switch. Was trying to describe the current path in simple ways to show that setting the switch to off makes it safe to remove that wire without shorting a wrench to ground.

[four winds]

Next time you start it, measure the battery voltage at the terminals first. Then after it is running measure again.

The voltage should be higher while running and slowly rise more as the alternator charges the battery. If it goes fairly soon to over 13 volts then chances are things are working well.

[johnlikesail]

I will do that, Four Winds. I did get a 12 volt reading though...when measuring alternating current (8.1 v was on my multimeter's direct current setting).

I am not great at understanding how my electric system functions (magic?). I did not know how to properly test an alternator.

I will measure at the battery as Four Winds suggests in two weeks or so when I put on the next round of repairs (new exhaust manifold, repair seawater strainer, replace secondary fuel filter, new fuel lift pump, and the DREADED ENGINE BLEED).

In the meantime, any thoughts on whether I should be paying attention to the reading in direct current or alternating current (I assume alternating b/c that reading was correct) when checking my batteries and alternator? Since I only read 12v...should there have been additional power coursing through that bare red wire? Same 12 volt AC (8.1 volt DC) reading with engine off, same regardless of engine RPMs.

Thanks!

[Wotname]

FWIW, the should be no AC voltage at all, especially when the alternator is stationary. Even running it should 0V AC unless it is faulty.

If you getting AC volts then either something is terribly wrong or you aren't using the meter correctly.

[johnlikesail]

Wotname:

I put the multimeter on the setting with a "V" and a squiggly line above it...I believe I was measuring alternating current at 12 volts. Thanks for your description that something could be "terribly wrong." I will think about that for the next two weeks.