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I have an older (but very solid) Snapper with a 12.5hp 2 cylinder Briggs & Stratton motor that is putting out 17.2 VDC to the battery and the PTO clutch. It has an unregulated dual circuit alternator with diode. The Briggs & Stratton motor model number is 404437, Type 011001, Code 85121912. It burned out the PTO clutch. Any ideas why or how this thing is putting this high voltage and what I can do to fix it? Loose magnets?

Is this under the PTO load? IF not what is the voltage with the PTO engaged?

You can add a voltage regulator if necessary but if the voltage is under 15.5 vdc it is within the safe operating spec of PTO clutch. Note these clutches do short out on their own over time.


Note- The dipstick in the image does NOT fit the opposed engines, you ,must find you own mounting position.

GMM said:

I have an older (but very solid) Snapper with a 12.5hp 2 cylinder Briggs & Stratton motor that is putting out 17.2 VDC to the battery and the PTO clutch. It has an unregulated dual circuit alternator with diode. The Briggs & Stratton motor model number is 404437, Type 011001, Code 85121912. It burned out the PTO clutch. Any ideas why or how this thing is putting this high voltage and what I can do to fix it? Loose magnets?

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It sounds like you may need a new alternator. Typically, a mower with an electric pro has a regulated alternator, which you may need to install.

Hello GMM,

They quit making a repair connector with the diode on the red wire for this style stator a few years ago. I would not go through the expense of replacing that style stator because it was not meant for an electric PTO application.

You have a "leaking"/open diode on the red stator wire at the harness connector. I do not recall the specifications for this particular diode.

As others have mentioned, you would be better off installing the small square regulator and make sure the body of it is mounted to a ground on the engine.

1N5406, 600V, 3 AMP
Briggs PN 391507

I have seen the 3 amp system work fine with a PTO on an Ariens Zoom 34 but upgrading by adding a regulator will provide a couple extra amps from the same stator.

I appreciate all of the good input, but have been unable to work on the mower this week. My thought, and I will need to check out a few more things before deciding on a plan of action, is to find out what has changed first.
I am thinking to remove the motor from the mower given that it has a horizontal crank (I think this will be easier) and then tear it down to replace the alternator (if it checks bad) or replace it with a new alternator that utilizes a regulator. I am trying to avoid burning up the new PTO clutch.