# Vintage B&S armature gap



## heymitduh (Sep 28, 2012)

:dazed:Hello group, just put a new armature on my B&S Mod.#300-421 (Cast iron, 12hp, circa. 1967). Having some ignition problems but what is confusing me is that in the service manual I'm using, it gives two different dimensions for the armature air gap.(.010 and.014"). That whole table lists multiple model series #'s with each line having two different gap settings and I can't figure out why. Can anybody help me out with this?


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## jhngardner367 (Apr 5, 2011)

Welcome to the forum !
You can set the armature to .012. That's a general clearance for them. Usually I set them at 
.010,without points,and .012/.014 with points.
An easy gauge for this,is to use a piece of cereal box cardboard between the armature,and flywheel ,and hold the armature against it,and tighten the screws.
If it has points,set them to .012/.014,and the plug gap at .030.


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## heymitduh (Sep 28, 2012)

Thanks Jhn...., went with the .014 and got a good spark. Now to get it started. I poured a thimble full of gas into the cylinder, put plug back. Thought that would at least give it a partial start, but nada. So now I'm tearing the carb apart. See what's going on there. Basically, cuz I can't think of any other areas that aren't ok to my knowledge. This engine hasn't ran in about two years although I had ran the gas out of it so it shouldn't be gunked up in there!


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## jhngardner367 (Apr 5, 2011)

Hold your palm over the carb inlet,and crank it. You should feel suction. If not,you have a valve staying open.
If you feel suction, roll it over,with the choke on,and squirt some fuel into the carb. If it fires,you should be able to run fuel into the inlet hose ,and see if it stays running,until the bowl is empty.


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## heymitduh (Sep 28, 2012)

Well, I got suction but no matter what I do, can't get it to fire! I tore the carb apart, cleaned it, put it back on block. Swapped plugs with the one on my push mower, they're the exact same. They both work on push mower. I reduced the armature gap to .010 but no change. You think I should change the point gap to .010? Calls for .020 and that's where it's always been, back when it ran. I replaced points and condenser mebbe two years ago and it ran after fine. The trouble started when a mouse or squirrel built a nest right behind the armature. But I replaced that and have spark but maybe not enough. I was thinking of comparing the spark on my push mower to the spark on this 12 hp. It is a blue spark on the 12hp but not real sparky, if you know what I mean. Mebbe its too weak to ignite fuel mixture. 
I don't want to take it to a shop but I'm getting close to that.


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## jhngardner367 (Apr 5, 2011)

Check the "kill" wire from the coil to the switch/junction screw. That mouse may have chewed it. Set the points at .014-.016,and see if that helps.


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## heymitduh (Sep 28, 2012)

I'll give that a shot. Tomorrow after work, I hope!
Bought a spark tester today and set the gap on it to 0.30"...I'm getting a good spark... most of the time. Think part of that was a poor ground at first with the spark tester or it could have been an issue with the ignition system.
If the capacitor was bad, I wouldn't get any spark at all, right? Was thinking of taking the points and cap off, examining them, testing the cap to make sure it's ok, and then put it back together, setting the points closer like you said.
When you install the armature, do you make sure that both sides of it are the correct distance away from the flywheel? Because the directions I've been following, tell you to put it up as high as possible, then put your feeler gauge under one side, loosen that side and the magnet pulls it down. Tighten that side back up. And then that's it....according to the Briggs and Stratton Manual. You would think that both sides of the armature should be gapped the same. .012-.014" 
I've checked all of the wiring and they all test ok.
It's a mystery to me. It ran ok up til a year or two ago. Didn't need it last year because the winter was so mild. (It's the driving force of my logsplitter!_
My Dad told me today that I could have a 12 hp Kohler that he has in an old Wheelhorse. That's an option but I'm not ready to give up yet! I appreciate your help jhn....will try your suggestions.


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## jhngardner367 (Apr 5, 2011)

When I set the armature gap,I usually have both legs loose enough to move,then I use a piece of oil-filter carton/cereal box cut in a 3/4"w, 4" l strip,as a gauge(it mikes @ .0125). hold the strip between the flywheel,and the armature(it is more accurate if the flywheel is set so that the MAGNET is away from the armature legs,since it's a flatter surface.),and push the armature against the flywheel,and tighten the screws. Then just turn the flywheel,as you pull on the cardboard strip.
A bad condenser(capacitor),can still give a spark. Sometimes they will run,until the engine warms up,and then the layers,inside,separate,and you lose spark.
You can try a .25microfarad condenser, from a early Chevy truck . it will get you a better spark,usually. Ask for one from,say a 1970 .


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## heymitduh (Sep 28, 2012)

Well, tried all of your tips but ....here's what I ended up doing. I am exchanging armature for an OEM unit. See, I dropped it straight out of the package (tile floor) and didn't think I had hurt it but I did notice later that the gap on the top, btwn the laminations wasn't square. I ended up straightening it out...you know how you'll try anything when you've tried everything else. Anyhow, I lost confidence in it.
I measured the caps I got, .276 uF and .216uF so I'll go with the larger? The one I got at the parts store only measured .203 and had a different bracket (wouldn't be able to use it) so I returned it. So I'm waiting for armature now.


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## jhngardner367 (Apr 5, 2011)

Yeah,the larger will do. As for the armature... yeah,dropping it COULD possibly damage it,and make it not work correctly. By the way,are you sure the points are ok/not grounding out ?
Also,if you can find a new-style armature,you can do away with the points,altogether! Find one from a 10-12 hp vertical/horizontal ,that has the same arch on the legs,and screw spacing,and try it. I've done this on a few of them.


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## heymitduh (Sep 28, 2012)

Yeah, I didn't notice how the laminations were initially spaced so wasn't sure if I bent them or not. After I still couldn't get a spark, I took armature and bent it square....actually bent it a lil' too far so I bent it back. That can't be good for it!

I'll check the points to see if they're grounded. Guess that's just a matter of putting an ohmmeter between each point and ground, eh?

Would be nice to do away with the points....have to look into that! See what's on my Dad's Kohler. It's about a '76 model.
Just waiting for the new armature now!


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## jhngardner367 (Apr 5, 2011)

The Kohler will have a battery/coil ignition,as an early model car had. It would require changing the ignition switch,and re-wiring for the new system. Magneto systems kill the spark,by grounding the coil,whereas, the battery/coil system(Kohler),has 12v fed to an external coil,and shuts off the12v,to kill the engine . 
The new armature you ordered may be a magnetron(pointless) coil. If so, just run the kill wire on the armature, to the wire from the switch(on the switch,it's marked "M" on the terminal). You don't even have to remove the points,if you don't want to,just by-pass them.


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