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powerking_one

Briggs Magnetron Stuff

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powerking_one
Edited some changes........................ Comrades, Well after seaching, and searching, and searching, I believe I have the answers to some of the (conflicting?) furvor on converting the old (pre-1980) cast iron singles(with a 2-pole coil and single magnet flywheel) to Magnetron ignition. Why some say it works, why some say it works without flywheel magnet re-polarization, but it starts harder/runs poorer now, and some say it plain doesn't work. My experiences cited are with the 394970 add-on Magnetron kit. For those of you that opted for the complete 398811 Magnetron coil assy, the plug wire is the correct length (I assume). Everything I've checked is via empircal methods including the use of a compass, DVM, timing light, and oscilloscope. My engine example is typical of others' discussions in this forum (model 243431 date code 1967). Fact: the magnet polarity is indeed reversed from other Briggs models the Magnetron module IS supposed to work on. I checked this on 3 different engines:130232, 191702, 90XXX? and their polarities are all NORTH(compass points SOUTH). Hence my 243431 magnet is SOUTH (compass points NORTH). The instructions state that it will NOT work unless it is installed on those CAST IRON or 2 CYLINDER engines "ORGINALLY EQUIPED" with the Magnetron ignition. This is true: A) the module ends up being on the RIGHT side of the coil (instead of LEFT). This position yields absolutely NO SPARK. IF you reverse the coil mounting 180 degrees, a few things change: A) now the spark plug wire is too short and has to be extended, B) you will have spark but at a 1/2 NORMAL VOTAGE LEVEL and at a much higher minimum RPM to achieve spark. Also, just as/more important, the ignition timing is SEVERELY OFF. Most L-head fixed timing air cooled engines should run about 19-22 degrees of advance. Now with the above condition, the Magnetron/coil is firing on the LEADING edge of the magnet instead of the TRAILING edge of it; hence we're adding 10+ degrees more advance! This explains a lot of the -hard starting- -backfiring- and (overheating?) problems some folks have reported. I verified all this with a timing light. If you move the coil mounting bracket all the way to the right, it still isn't enough retard to get the the timing in the correct ballpark (and you still have the reduced spark voltage condition). As for why the voltage is 1/2 now, it's because the Magnetron is firing too early (coil is only charged on the the "push" cycle of the leading edge magnet passing over. Normally, the points close(or open on some engines) when the magnet passes over the trailing "push to pull" side of the coil. Bottom line: without flywheel magnet re-polarization on these old girls, we have a totally MARGINAL ignition operating condition due to half the normal spark voltage and incorrect timing. Attached is a crude schematic I drew (stop laughing!), but shows the system. Now if I can just find somebody local to re-magnetize my flywheel. Hope this helps, Tom(PK)

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roma3112
hmm you make perfect sense to me now all i have to do is decide if i should have my spare flywheel repolorized or just replace the manetron coil with the standard coil/points setup. this old girl just hasnt been the same as i rember her from my childhood, having you explain it in terms of having the ignition toming way off explains alot. i think i will price out the cost of an old/new coil and points setup tomorrow. thanks john b

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Dutch
Tom, Are you stating flywheels must always be repolarized? I've never had to repolarize a flywheel when converting to magnetron, and the engines have run flawlessly. Maybe I've just been lucky.

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powerking_one
Herb, One other caveat I didn't mention in my diagram and explanation above, is also the coil/spark voltage is reversed and negative if the coil is turned around 180 degrees ;ie spark direction is FROM the ground to center electrode. This may not be a problem, but not it's not typical/standard anymore. What I tried to clarify and explain was some of the mystery in peoples' (conflicting at times) experience installing the Magnetrons on the 10,12,14,16 HP CI singles out there. An older message thread I found on the club refered to another message in which someone had info that nailed down exact SN (Code) ranges of engine with the correct polarity; I couldn't find it. To my way of thinking a "marginal" condition means: -----intermittent operation--------sometimes it works, sometimes it doesn't-----yes it works, but it's right on the hairy edge of not working and too far away from the desired centerline of design tolerance-------- it works, but I had to change/modify a bunch of other things in the system to do so------------etc--- With my engine (test case), I did get spark; it was faint ,skinny and not a good blue color. I retarded the timing (coil mounting bracket all the way to the right) and estimate this still was around 25 degrees BTDC. Then I had to extend the plug wire(used mil-spec HV RTV, solder spliced, adhesive lined heat shrink tubing). The engine started but it took a few revolutions 4-5 for it to "pop". Before, it'd usually pop on the first compression stroke. I think most folks who know about a "marginal" system or condition would opt to relieve or correct it. If the compass points North at the magnet, the plug wire comes off the back side of the coil (large head of rivots at the back of it as well), then you have one of these "exceptional" Magnetron upgrade canidates. Tom(PK)

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roma3112
WELL THE VERDICT IS IN AS FAR ASS MY 3112H AND MAGNETRON, i just finished the re-conversion back to the factory coil and breakerpoint setup. The thing runs great now!!!! just like i remberd it did, 2 0r 3 revolutions and a lil choke and presto. I cant imagine i suffered with the thing the way it was chasing down carb problems and fowled plugs galore, all to have it trace back to the mismatch of an older engine and magnetron setup. As far as i am concerned i would reccomend any members out there think twice before upgrading without repolorizing a flywheel, and even then the need for the engine to spin faster to generate the same spark is still up in the air.

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Jef
Thank you Tom for the time you spent researching this. I hope everyone takes note. I for one have seen this three times and repolorization has cured the problem all three times. I have posted this in the past but I hope this wiill put it to rest. Just a note to all once again Briggs will repolorize for free just send them your flywheel with your request. Sorry I don't have the address at the moment. But I know other members might. Once again Thanks Tom. Jeff

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powerking_one
John, I think the verdict and jury decision is already in. Running an ignition system with 1/2 the normal spark voltage WILL yield symptoms you've agonized over with(Champion spark plugs, fouling, hard starting, lots of plug carbon buildup, etc). Re-polarizing the magnet with the Magnetron should result in better performance than the points/condenser system. Actually, these big CI larger diameter flywheels give BETTER low RPM magnetics/spark than the smaller engines(due to higher net surface speed); that is if the rest of system is all correct. Tom(PK)

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PatRarick
Thanks for the time and effort put into this, Tom. It answers a lot of questions and should eliminate quite a few headaches for those desiring to convert to Magnetron. Pat

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