Ignition tester

[chuckw]

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]

Those used to available through the club’s Ships Store. Apparently they no longer sell them.

[billw]

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.

Long live American manufacturing!

[The Boat House]

• This reply was modified 5 years, 5 months ago by The Boat House.
• This reply was modified 3 years, 2 months ago by The Boat House.

[chuckw]

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

[joecb]

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]

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]

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

[fisherman6]

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

OldJohnnyRude on YouTube

[Mumbles]

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

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