A confession and a question

[Jrblanke 857]

Good morning amigos!

I have a question for you guys. First of all, I confess that I do not understand the difference between a magnum motor and an old K series motor. I understand that the K-series has points, and a magnum does not. But I have intentionally (I know I know…typical lazy millienneal l behavior) never investigated or bothered to understand how the magnum motors throw spark. This is probably because ive never had a “no spark” problem with my magnum motors. They just work. SO the reason I bring this up, is because I wanted to make it known that I don’t fully understand the electricals on my magnum motors.

 

With that being said, I also don’t understand how they charge. My issue, and reason for making this post is because I am picking up a 312-8 from a friend this weekend and he said the only issue is that the machine is not charging. I am wondering how do I trouble shoot this, and what are potential parts I need to look for at the big show to make it work.  The previous owner mentioned to me that he used a volt meter and found that the he wasn’t getting juice from the middle plug coming from somewhere (its been a few months). Is it a rectifier or voltage regulator maybe? Its definitely a magnum motor and not a starter generator motor.

 

Thanks,

[953 nut 55,223]

James, it could be as simple as a blown fuse or a wire with a lot of corrosion on the end. With the key ON and engine not running there should be battery voltage (12 volts +/-) on the center terminal of the regulator, it won't work without it.

[Pullstart 62,853]

I too have limited Magnum knowledge.  I’ve toyed with a couple before, but don’t “know” the system like I know K series.

[Achto 27,571]

23 hours ago, Jrblanke said:

I also don’t understand how they charge.

 

The K's and the Magnum's with a bendix starter have magnets inside the fly wheel that spin around a stator to produce AC electricity. The output from this should be around 30-40 volts AC. These AC leads are connected to the 2 outside terminals on the voltage regulator / rectifier. The reg/rec converts the AC voltage to DC voltage and regulates the output to around 14 volt DC. The DC output is from the center terminal on the reg/rec. This terminal needs to have battery "+" voltage when the key is on or the system will not work. ( battery will not be connected to the reg/rec.)

 

First check to see if you have AC voltage from the stator with the engine running 3/4 throttle or above. Unplug the reg/rec and probe the 2 outside terminals on the plug with a multi meter set to AC. You should have 30 to 40 volts AC. If this is working properly then move on to the reg/rec.

 

1 - Make sure the body of the reg/rec is properly grounded.

2 - Make sure there is battery voltage to the center terminal on the reg/rec with the key in the "ON" position.

 

If the above check out & you do not have 13+ volts dc at the battery with the engine running then you have a bad regulator / rectifier.

Edited June 17, 2022 by Achto

[Achto 27,571]

1 hour ago, Jrblanke said:

never investigated or bothered to understand how the magnum motors throw spark.

 

Spark is achieved by having a magnet on the flywheel pass by a magneto coil, same as any pull start only engine. Older engines still used points with a magneto, later engines used an solid state or electronic pickup instead of points.

Edited June 16, 2022 by Achto

[Ed Kennell 38,170]

Dan has you covered James.     I will only stress Dans #1. bullet....make sure the RR body is well grounded.

[peter lena 8,625]

@Jrblanke  quick check , have any alligator clip test wires ? go from battery cable ground bolt point , to rectifier engine tin mount area bolts , also dielectric grease the plug on wire end plug in . see if that gives it life . pete

[Jrblanke 857]

Fantastic info guys! I pick up the tractor tomorrow night, so I'll report back my findings this weekend!

 

Thank you all, very much!

 

James

[squonk 41,104]

Hold all your bets! 89 312-8 uses the single wire diode charging system. Another kettle of fish! 

 

 

Edited June 16, 2022 by squonk

[Achto 27,571]

39 minutes ago, squonk said:

Hold all your bets! 89 312-8 uses the single wire diode charging system. Another kettle of fish! 

 

Stators rarely go bad. Biggest issue I've come across with the single wire system is a bad diode. Simple fix usually.

 

Start the tractor, disconnect the charging wire & see if it is producing AC or DC voltage. Test leads from the wire to the block. If you have AC voltage then just replace the diode. No voltage, bad stator or magnets on the fly wheel.

Edited June 16, 2022 by Achto

[clueless 2,991]

8 hours ago, squonk said:

Hold all your bets! 89 312-8 uses the single wire diode charging system. Another kettle of fish! 

 

 

Guess he will have to figure out what year the 312-8 is  my '88 has a 15 amp reg bolted to the front of the flywheel tin.