Briggs Magneto igniton.

[adsm08 2,717]

So now that Spring and good weather are back I'm back to the Speedex. I'm getting ready to start painting, but the weather has been too wet, so I've been working on the engine.

 

Where I am right now is no spark. It is a Briggs 8HP (per spec sheet, data tags are gone) with a points/condenser magneto ignition system, dating to the late 50s or early/mid 60s.

 

I'm annoyed with it and really just want the engine to run, so I am looking at converting it to solid state, as the flywheel magnet is still in good shape. But without engine data tags I am not sure which coil setup to get. How interchangeable are they? It looks like there are only a few different styles. Are these things truly plug and play.

 

Also, it looks like this engine has a flywheel alternator, which I'm not super familiar with. It has armature windings under the flywheel, magnets inside (all intact) and what looks like it is probably a rectifier, but not a true regulator on the engine cover. Then there are two mystery plugs back at the battery end of the engine. I'm assuming at least one would be for battery charging. Not sure what the other is for.

 

You guys seem to, collectively know everything, so I'm hoping someone can shed some light.

[WHX?? 50,785]

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1 hour ago, adsm08 said:

Are these things truly plug and play.

Yes for the right motor. Not sure if it works on a motor that has charging coils. 

@Achto has done a few more than I have hopefully he'll chime in. 

[Handy Don 13,340]

It sounds like you have a stator and diode system for charging in addition to the magneto for firing the engine.

The magnets flying past the stator wiring generate alternating current and a diode lets the "plus half of the wave" through to charge the battery and blocks the "minus half".

 

I have only one B&S that works that way, a 12.5 hp vertical. There were two wires coming out of the stator into a molex connector. On the other side, one wire led to the diode and then the battery and the other was grounded, which makes good sense. Hidden away near the battery was another two-prong socket that, from the circuitry, I believe was intended to hook up lights or some other power-needing accessory for, I think, a higher-optioned version of the unit I have. I've never used it. (Many Tecumseh snow blower engines have a similar way of powering the headlights and/or heated handgrips.)

 

Sorry, cannot help at all on the magneto-points-condenser ignition.

 

Good luck!

[Achto 28,806]

6 hours ago, adsm08 said:

It looks like there are only a few different styles. Are these things truly plug and play.

 

Briggs & Stratton solid state coil part # 398811  or aftermarket equivalent fits 7hp-16hp engines. If your engine has a cast iron block the magnets on the fly wheel may have reversed polarity compared to the aluminum block engines. If this is the case then you only need to install the solid state coil backwards to make it work.

 

One other option if your points are not under the flywheel, is to install an automotive coil with the existing points. Just like a K model Kohler uses.

Edited May 18, 2022 by Achto

[adsm08 2,717]

46 minutes ago, Achto said:

 

Briggs & Stratton solid state coil part # 398811  or aftermarket equivalent fits 7hp-16hp engines. If your engine has a cast iron block the magnets on the fly wheel may have reversed polarity compared to the aluminum block engines. If this is the case then you only need to install the solid state coil backwards to make it work.

 

One other option if your points are not under the flywheel, is to install an automotive coil with the existing points. Just like a K model Kohler uses.

 

My points are under the flywheel. IIRC the battery ignition system on my 800 with a similar Briggs engine is set up like my K181.

 

I got some more time at the end of the day at work and started sanding the engine cover, and once the rust was removed I found the engine stamping numbers. Got ahold of my local lawn equipment shop, and after running through about 5 supersessions they also came up with same 398811 coil. I should have it by Thursday.

 

3 hours ago, Handy Don said:

It sounds like you have a stator and diode system for charging in addition to the magneto for firing the engine.

The magnets flying past the stator wiring generate alternating current and a diode lets the "plus half of the wave" through to charge the battery and blocks the "minus half".

 

Right, basically an automotive alternator turned inside out, with a similar type of voltage rectifier.

 

 

3 hours ago, Handy Don said:

 

I have only one B&S that works that way, a 12.5 hp vertical. There were two wires coming out of the stator into a molex connector. On the other side, one wire led to the diode and then the battery and the other was grounded, which makes good sense. Hidden away near the battery was another two-prong socket that, from the circuitry, I believe was intended to hook up lights or some other power-needing accessory for, I think, a higher-optioned version of the unit I have. I've never used it. (Many Tecumseh snow blower engines have a similar way of powering the headlights and/or heated handgrips.)

 

Sorry, cannot help at all on the magneto-points-condenser ignition.

 

Good luck!

 

What I believe is the rectifier has three wires going to it.

 

I also have a pair of two, what I would call "barrel connectors" back by the battery. I am assuming at least one is for charging the battery, but I don't have the other end of either, so some modifications will be needed there. Once I have it running I will begin voltage testing there to determine what's what. I'm actually pretty good at reverse engineering things, once I understand the system's basics. Some of these small engine systems are so simple compared to what I'm used to working on that I can't figure them out.

 

I also can't figure out why a magneto needs points, or how it uses them, but that's not super relevant anymore. Thanks guys.

 

[Achto 28,806]

8 hours ago, adsm08 said:

My points are under the flywheel.

 

Sounds like you have an aluminum block engine.

 

8 hours ago, adsm08 said:

after running through about 5 supersessions they also came up with same 398811 coil. I should have it by Thursday.

 

When you get your new coil, leave your points installed on the engine. Just cut the wire that goes to them. This will keep oil from leaking out of the push rod hole for the points. There should be writing on the new coil instructing which side goes towards the cylinder, install correctly, set your gap to the flywheel, run a kill wire to the terminal on the coil, (ground this wire to kill the engine) Job Done.

[Handy Don 13,340]

12 hours ago, adsm08 said:

why a magneto needs points

Enables a more precise setting for timing the spark