Mark 20 no spark

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ronboonville
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Joined: Tue Mar 10, 2015 12:38 pm

Mark 20 no spark

Postby ronboonville » Sat Apr 14, 2018 12:09 pm

I replaced the condensers, disassembled, cleaned and polished points, replaced plug wires, sealed cracks in coils with corona dope and checked resistance between coil and plug wires as 4.3. Checked air gap and cannot get a spark. Think the coil is too weak? points bad? Scintilla bendix mag. Something obvious. With this type do I need the flywheel on when I spin it?

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Richard A. White
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Re: Mark 20 no spark

Postby Richard A. White » Sat Apr 14, 2018 12:51 pm

I think yes as the points cam is on the flywheel, but I could be wrong

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green thumbs
Posts: 283
Joined: Mon Jul 06, 2015 1:21 pm

Re: Mark 20 no spark

Postby green thumbs » Sat Apr 14, 2018 1:31 pm

Mark 20 has magneto 301-73. Cam is on magnet rotor
Swapping in KNOWN good coils and condensers would narrow the field of possible problems. Be aware that for a spark to jump spark plug gap under compression requires much more voltage that to jump same gap in open air.
Coils with internal leakage may show a spark in open .but, ground out internally rather than thru spark plug when under compression.

Compare your reassembled points with a set that works...Murphy's Law states when it is
equally likely to assemble something correctly or incorrectly , chance favors the wrong way.
I am well acquainted with Mr. Murphy's Laws...unfortunately.
About all I know of subject.
Louis
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Mark 20 Bencix 301-73 001.jpg
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Mark 20 Bencix 301-73.jpg
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ronboonville
Posts: 93
Joined: Tue Mar 10, 2015 12:38 pm

Re: Mark 20 no spark

Postby ronboonville » Sat Apr 14, 2018 1:43 pm

green thumbs wrote:Mark 20 has magneto 301-73. Cam is on magnet rotor
Swapping in KNOWN good coils and condensers would narrow the field of possible problems. Be aware that for a spark to jump spark plug gap under compression requires much more voltage that to jump same gap in open air.
Coils with internal leakage may show a spark in open .but, ground out internally rather than thru spark plug when under compression.

Compare your reassembled points with a set that works...Murphy's Law states when it is
equally likely to assemble something correctly or incorrectly , chance favors the wrong way.
I am well acquainted with Mr. Murphy's Laws...unfortunately.
About all I know of subject.
Louis

right cam is on the rotor. air gap was at the rotor. new condensers. Is there a test for the points as far as resistance?

green thumbs
Posts: 283
Joined: Mon Jul 06, 2015 1:21 pm

Re: Mark 20 no spark

Postby green thumbs » Sat Apr 14, 2018 2:25 pm

My experience with electricity goes back 70 or so years...I was nearly electrocuted. An experience that has tended to keep me and electricity at an arm's length plus 10 feet.
That said and...the path from coil thru points should be checked to be sure it is not
grounding out due to misassembly of the small items and of course keep in mind that
metals conduct, oxides insulate...dirt and crud will either conduct or insulate depending
on which is most inconvenient.
I have several point sets from K1-6 apart at moment that are severely corroded. If better
points were available I would trash them. Not an option, so they await some miracle rust removing solution.
There is a lot of effort put into salvaging Bendix coils. I have not tried that route. Until and
unless our friends in China take an interest the only option.
I looked into haveing core rewound and was quoted $250 to 300. I guess that is a one off price not for a series run. WAY too much in any case.

In the late 1970s or early 1980s Toro went to solid state ignition and offered Guaranteed to Start for years of use. In 1983 I bought a Toro walk behind lawnmower for a 1/2 acre yard.
NEVER failed to start even when compression said mower was worn out. Same with the
following 2 replacement Toro mowers which I picked up used.
I also picked up a well used Toro showthrower that still had points....that was a bear to start
until I got fed up and did a thorough rebuild of ignition and fuel system...then it was as easy
to start as lawnmowers.

I had a young friend with a Maytag gas engine that defied his best efforts UNTIL he replaced
the NEW spark plug with a spark plug from an engine that ran well.
New Champion Spark Plug was defective. Rare, but, as the saying goes "They don't make them like they used to."
Louis
I have and use the Bendix Magneto Rotor tools. I have seen rotors that were removed by
prying...cracked and bent. The correct tools are very much worth having just for the time
they save.
Again I AM NOT anyone's idea of an expert in these matters
0.020" for new points and 0.018" for used points seem pretty much the rule for Bendix
Repco/Phelon, Wico and Eisemann magnetos.
Points are a switch...on and off...coils and condensers have values to measure
Louis
Louis


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