Spark Gap Tester

[ronsealdeath]

Hi there, can't get one of these easily over here, can I use a homemade one as in the attached picture? I am a bit worried it may do something bad to my ignition system, is this a risk?

Also on J. Reeves' timing for WOT guide, why do I need of of these devices connected?

Cheers

 

[oldcatamount]

Re: Spark Gap Tester

I made a spark tester once (still have it) and it does the job without any damage to the electrical system at all. The idea is not only testing for spark but testing for the strength of the spark ie: jumping the 7/16. You need a strong blue spark and it should make a "crack" sound when it makes the jump

 

[jonesg]

Re: Spark Gap Tester

You can use an old distributer cap from a car to make a multi cylinder tester, a metal disk on the center pole will establish the 7/16th inch gap.

 

[Jerry_NJ]

Re: Spark Gap Tester

Don't worry about damaging your ignition system, the worst that can happen is you'll get a misleading result.. e.g., a spark that you think is ok, but it is too weak. The 7/16" rule is a good one often quoted. For me I just want to see if there is a spark, so I use an old spark plug at about 0.1" gap. I think a good pop indicates a good ignition. Or at least tells you to think about the fuel system if you're checking the spark because the engine will not start.. or run well. Here I assume a lot, fresh gas/oil and good spark plugs with the correct gap.

 

[Craig-]

Re: Spark Gap Tester

I made this one and like using it better than the single plug at a time tester.
The flat lid of a mason jar works for the center grounding plate even better.

http://forums.iboats.com/showthread.php?t=423333

 

[jtexas]

Re: Spark Gap Tester

The risk of damaging an ignition component comes when you run or crank the engine with spark plug leads floating.

A floating lead doesn't really do anything - but - there is high voltage on that wire -- at least 15,000 volts at cranking speed, up to 30,000 or more with the engine running, and that much voltage will seek a path to ground [or "Earth" as it's called in places where you say "cheers" ], and can arc a pretty good distance. You don't want it grounding through something important. It's not a lot of current, just high voltage.

So, anytime you turn the engine over with spark plugs out, either disable spark by pulling the emergency lanyard (if equipped), or ground the leads to the block with jumper wires, or a spark gap tester.

For the WOT timing procedure, the #1 plug lead needs to be grounded, so your timing light can read the signal. And, plugs need to be out, so there's no chance of the motor actually starting during this test.

 

[tashasdaddy]

Re: Spark Gap Tester

i use this one, for years, without problems.

 

[ronsealdeath]

Re: Spark Gap Tester

Thanks for all the useful replies. I have got some bits together now to make a basic tester. Going to ground (see I'm learning!) it out properly too

I'm checking this just because I like tinkering but it should tell me a bit more about the condition of the engine I hope. If I am getting poor spark what are the major causes of this? From posts it looks like coils/Power Pack?

My engine is a bit of a dog at idle so I'm going through as many diagnostics as I can to see if I can rectify it.

Cheers