OT: BS engine

Have a 16 horse cast iron B&S engine (circa early 70s) with a no spark issue. I replaced the pickup coil but still no spark.
My question is weather or nor not the flywheel magnet should make continuity with the flywheel and thus the rest of engine as it does.
I realize the replacement coil could be bad however was taken from a running unit.

no. the rust must be sanded off by hand to make the parts shiny, then use a manila folder (single thickness) to set the distance. .004 or .005" is OK. Jim

(quoted from post at 18:21:43 09/02/16) no. the rust must be sanded off by hand to make the parts shiny, then use a manila folder (single thickness) to set the distance. .004 or .005" is OK. Jim

Click to expand...

Not to be contrary, but Briggs recommends a lot of different setting for their engines, but most are .010 to .012. :wink:
IMHO .004 to .005 is too close.

Irv

The rust is newish, was cleaned and gap set with a doubled over new $1 earlier in the year and a bill still freely slides between coil and flywheel today.
Been sitting uncovered for last few months while I putter on 'other' projects.

I don't know if it matters to the standard coil, but Magnetron coils can't be used on the old cast iron engines because the polarity is different in the flywheel. Did the coil come from a cast iron engine? Have the points and condenser been changed?

Hadn't thought about a difference between CI and alum block.
Points and condenser were taken out of service before I got it.
It ran for 4-5 years for me this way. Ran like a hit - miss but it ran

I've been battling the same thing on my '73 I ended up converting the points to a battery ignition. Read that thing about the reverse polarity, one guy I talked to sent his points flywheel back to Milwalkee and briggs re-polarized it for a magnetron coil.

'Course I had to try one of those add on electronic ign modules with the points coil without changing the magnets..... Got spark, just wrong timing, wouldn't run, only backfire.

Have you tried disconnecting the kill wire to see if it will spark?

Can you try the coil back on the engine it came off of, see if it will spark?

Can the flywheel from that engine be put on this engine?

So if I read your question right and this is what you were actually trying to ask; so here goes. You want to know if it is acceptable for the magnet segment in the flywheel to have continuity (or have contact with) the metallic section of the flywheel? Yes it does have continuity with the flywheel, not sure if it is press fit or uses some other attachment method. In the end it does not matter, the magnet only needs to produce a magnetic field. Then as that field passes a conductor or multiple conductors of the coil primary windings in this case it produces electrical energy. Which according to the B & S website will happen even if the magnet is rusty. I think the poster who shared the polarity may be wrong might have the answer for you of what is keeping your engine from running.

Kill wire disconnect was first test I did.
Engine this coil came from was running till piston grenaded, saved what was savable, the coil, scraped the rest.

Jim's 0.004" to 0.005" or your dollar bill is too little clearance. A business card or .010" is typically what Briggs specs.

Too close and the flywheel will contact the "armature" if there's any main bearing wear, and Briggs says they will typically "fire" up to a .030" gap, though timing will be a bit retarded.

And a little surface rust has no effect on spark.

One more thing, on some engines the coil (which Briggs calls an "armature") can be installed "flipped" front to back, and won't fire if backwards.
Briggs spark theory, Scroll down to Ignition Coil

Urm, thanks as that was I was unable to recall and was asking about.
I 'thought' it should but too many years have passed for me to recall it all.

Bob, thanks to you also as the gap specs I was unable to locate while I was puttering with this unit.
The link will be a big help in my quest of knowledge (be skeerd very very skeerd)
When I got this thing it needed a head gasket during which I figured out armature was in fact on backwards.
It ran this way but was down on power so flipped it over and power was up. Ran for a few years.
Late spring this year it stopped firing up and just now getting back to trying to get running.

It appears the coil has been rubbing the magnets and that is a spark killer.

I would remove the coil. Use a wire brush on a drill and clean the rust off the flywheel and the end where coil comes in contact with magnets.

Then use 3 one dollar bills as a spacer. Put bills between magnets and coil and tighten coil in place.

Let us know if it works. Geo

Permeability of the rust is better than the air it replaces. Don't worry about it. It will rust again anyway and the motor will still run. On the magnet being backwards what that does is determine the timing of the impulse; may be a factor, see below.

As the magnet passes the coil it generates a sine wave of current in the windings which make the full 360 +/- degrees plus a little ringing of what's left of the energy in the core. Since "magnetrons" ( a term Raytheon Corp. assigned to an electromagnetic microwave emissive tube....common usage RADAR and microwave ovens; a "trigger word" recently picked up by a small engine mfgr.) are inductive pickup devices without the need for any supporting electronics, if it doesn't run, and the magnet being backwards, it comes down to whether the plug fires adequately on the polarity of the pulse that occurs at the BTDC position necessary for operation. Research had been done on the polarity of plug voltage and the erosion of the electrodes.... aka ion migration.

Course the gap is part of that too because the gap determines the coupling between the magnet and the iron core of the magnetron (pickup coil) and as the coupling changes the intensity of the signal changes which changes the timing.....the plug fires at a certain voltage and the higher the applied sine wave, the faster you reach that voltage.

If you have an ignition point system, you don't need the flywheel magnet. The points close, allowing energy to collect in a remote coil and at the preset mechanical time, they open and the coil releases that energy into the plug.

I know this much. Half a woodruff key (flywheel to crank shaft lock) in a partially sheared condition is enough to throw the timing off enough to prevent satisfactory operation. BTDT