Ignition tester

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chuckw
Posts: 70
Joined: Mon Mar 09, 2015 7:23 pm

Ignition tester

Postby chuckw » Mon Aug 06, 2018 4:22 pm

Many years ago Dick Fuchs showed me an ignition tester that he had. It works by pressurizing a spark plug and then pulling the engine over. i got one and have used it regularly until now when it will not pressurize. It was made by Dixon, Inc in Grand Junction, CO. Their number is no longer in service. Does anyone have one of these or know where to get one or have one for sale that works?
Thanks,
Chuck Webster
Arlington, VT

Jerry Ahrens
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Location: Lake of the Ozarks Mo.

Re: Ignition tester

Postby Jerry Ahrens » Mon Aug 06, 2018 6:44 pm

Those used to available through the club's Ships Store. Apparently they no longer sell them.
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BillW
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Re: Ignition tester

Postby BillW » Tue Aug 07, 2018 5:56 am

In my opinion, those were really more of a spark plug tester, than an ignition tester. Sure, they tried to simulate combustion pressure but didn't take into account atomized fuel, oil, etc. They were, IMHO, nothing more than an interesting novelty. All you really need to test ignition is an open-gap tester set to at least 1/4". Those are available everywhere.

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Tubs
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Re: Ignition tester

Postby Tubs » Tue Aug 07, 2018 10:30 am


For those that may not have seen these things they
are a inexpensive device to simulate the same test
as this AC plug tester. Unless the cylinder is damaged
replacing the O rings and a little Vaseline should get it
to pressurize again but I don't think they create enough
pressure to be of much value. The ignition capabilities
are you have a spark or you don't. Its what I use them
for. Much easier than trying to ground out a spark plug
against the block while pulling one over. These, an ohms
meter, parts to substitute, and decades of experience is
the extent of my ignition testing equipment.
Spark plug testor.jpg
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chuckw
Posts: 70
Joined: Mon Mar 09, 2015 7:23 pm

Re: Ignition tester

Postby chuckw » Tue Aug 07, 2018 3:29 pm

The one on the left is the one I have. I will replace the o rings and see if that works. thanks

JoeCB
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Re: Ignition tester

Postby JoeCB » Tue Aug 07, 2018 4:02 pm

I have one of the "pressure spark testers" as well , hardly ever use it. Can anyone explain why spark jumping a gap under higher air pressure is any more of a valid test than spark jumping a larger gap in normal atmospheric pressure? I can't see that there would be any difference.


Now, re- reading the previous post about the AC SPARK PLUG tester, I think that I can see some advantage in testing a spark plug under higher air pressure... maybe detect a bad seal or cracked insulator.

Joe B

Chris_P
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Re: Ignition tester

Postby Chris_P » Tue Aug 07, 2018 6:37 pm

Joe,

Because a cylinder is under pressure during combustion. Holding a spark plug against the block and getting a spark tells you nothing really, other than that your ignition system could make spark under no compression situation. Doesn't really help you in the real world. I have seen MANY motors create spark in open air, then fail under compression. Always test spark under compression.

EDIT: I just read your wording, you mentioned opening the gap for open air tests. Didn't catch that the first time around sorry. Most guys I see hold the plug against the block and when the spark jumps the electrode gap they call it good, which it may not be.

JoeCB
Great Lakes Chapter President
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Re: Ignition tester

Postby JoeCB » Tue Aug 07, 2018 11:57 pm

OK , thanks Chris. I do understand the "hold the plug against the block" issue is far from a definitive test, but still looking for why "under compression" is any more valid than a wide gap test. Now maybe someone with more electrical smarts than I can come up with a chart comparing a given spark gap at various pressures ( PSI) against wider gaps in open air. My rule of thumb is that a good coil should be able to jump a spark across a 1/4 " gap in open air.

Joe B

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Fisherman6
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Re: Ignition tester

Postby Fisherman6 » Wed Aug 08, 2018 9:19 am

Joe,
My understanding is that a compressed fuel/air mixture has a significantly higher resistance than open fresh air at atmospheric pressure. I do not know what the numbers are, but the 1/4" gap is supposedly on the conservative side of a good spark for a typical magneto ignition to fire under compression. It is a rule of thumb that seems to work for me. I have had a few engines that would make a plug spark in open air and look OK but would not fire at all under compression. If it will jump a 1/4" gap in open air and the plug is good it has always been able to fire under compression for me so far. I

I would have assumed that the fuel mixture in the compressed air would have also increased the resistance beyond what simply compressing the air would. I do not know for a fact what effect the fuel mixture has on the resistance across the plug gap though. If the subject ignition tester actually tells a person anything, the fuel must not have much of an effect.
-Ben
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Mumbles
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Re: Ignition tester

Postby Mumbles » Wed Aug 08, 2018 10:40 am

Cheap and simple items here for testing spark with a 1/4" gap.
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