How to install a ARMATURE-MAGNETO on a BRIGGS &STRATTON 18 H. ENGINE? Is there a certain gap between the fly wheel and the armature-magneto?

If it's a magneto or ignition module then its a kill wire. I know of no Briggs and Stratton engines that used battery powered ignition. So connecting the kill wire to the armature of the magneto (ignition module or engine case) will prevent spark.

The gap between the flywheel and magneto (pick-up coil) is not that critical, if your engine is not running right or won't start. 2 to 3 mm is fine. The key point is that the gap be uniform in the arc where the fly wheel passes it. Please post your symptoms and we can better assist you on the forum. If you are not getting any spark from the plug wire... check this at night by unplugging the plug boot and pulling the cord and watching; if you can't detect a spark... then you have a magneto issue or a bad spark plug wire. A little crokus cloth to rub the rust off the entire flywheel edge surface will help. Don't sand down or apply solvents to the magneto surface even if it's rusty!

check the valve adjustment if overhead valves

did you replace the armature or the magneto?the magneto has the plug wires on it the armature charges the battery if you put on a new magneto annd you have no spark check the safety switches

a simple way to set the gap is to use a couple of regular business cards (2) stacked on each other, loosen the magneto and let it fall onto the flywheel, with the cards in between, and then tighten the magneto hold down bolts, and spin the flywheel to remove the cards, with the gap you have the motor is fighting to fire and is doing so too slow, which is causing the backfire,

The magneto is self contained and the primary winding is grounded via the throttle stop, flywheel brake, or the low oil level sensor to ground the magneto enough to stop the spark from jumping the spark plug gap.
First check the oil level and make sure it is fully serviced.
Second check the Flywheel brake switch to see of the cable needs re-adjusted or replaced. There is a lever on the brake actuator that makes a ground on the primary of the magneto. ANY gound on the wire that goes from the flywheel brake, the throttle control (if so equipped) or the low oil level sensor will stop the engine from having spark. There is no condensor. The magneto is excited by the magnet in the armature each rotation of the fly wheel. Grounding of the magneto primary rreduces / stops the function of the magneto high voltage output.

You need to find out what is grounding the magneto primary when the engine should be in a running state.

Thanks for choosing FixYa,
Kelly

If you know the model number of it, this chart will surely tell you. I'm assuming it is probably a Briggs and Stratton engine. The air gaps vary say between .006" and .020" . Most of the time, on smaller engines like yours, .010" is suitable and works well. Here is the chart for All Briggs engine models. I use a business card to adjust because a feeler gauge sticks to the magnets.
Look in the third column from the left under armature air gap.

http://www.briggsandstratton.com/engines/support/frequently-asked-questions/~/media/71BB9DA0BD4D4C19A0DA611923A0B80A.ashx

no generator or alternator power generated by magnetic pulse[magneto]on the top of motor the fly wheel has magnetic inserts that pass thru a armature/coil causing a pulse sometimes the flywheel gets surface rust but that would also affect spark --check connections and test battery battery may not be holding charge or loose or corrosion in wiring can cause battery problem

Bob, if you have the flywheel back on, first check the air gap between the magneto (ignition armature) at the magnets on the flywheel (a common business card works well for this) then unplug the small wire from the magneto and check for spark, if you have spark, repair the kill switch and/or wire, if NO spark, replace the magneto.
If you remove the spark plug, you can hand spin the flywheel fast enough to ascertain spark

The air gap for the magneto is .010 - ,014. A microfiche card, an index card, a common business card or anything NON-magnetic of the above thickness makes a good shim to achieve this gap.

1. Remove the old ignition armature mounting screws. Then, disconnect the stop switch wire from the flywheel brake and remove the armature.
   
2. Attach a replacement armature from the original engine manufacturer, using mounting screws. Then, push the armature away from the flywheel and tighten one screw.
   
3. Turn the flywheel so the magnets are on the opposite side from the ignition armature.
   
4. Place the appropriate shim between the rim of the flywheel and the ignition armature. While holding the shim, turn the flywheel until the magnets are directly adjacent to the armature.
   
5. Loosen the tight screw so the magnets pull the ignition armature against the flywheel and shim. Then, tighten both mounting screws and rotate the flywheel until the shim slips free.