# Spark Tester



## Brian Rupnow (Aug 7, 2013)

Okay--I have to admit, that up until yesterday, I hadn't heard of a "spark tester". For me, it was good enough to lay the sparkplug out on the engine block to see if I had any spark, or to grit my teeth and hold onto the coil wire, waiting for that incredible ZZZZAP!!! Yesterday I received my first ever CDI ignition package from S&S Machine and Engineering, owned by Roy Sholl. Roy has warned me, both in the instructions and by email, to not let the cdi fire unless you were sure that the high current had a GOOD path to ground, otherwise it could fry the CDI and the Hall effect sensor. I dug around thru all the literature that was on the CD that came with the CDI system, and found a picture of a spark tester. I could have probably ordered one from Roy, but between shipping charges and the time factor involved, I decided to make my own. I don't have any insulating plastic or nylon around my shop, but I do have lots of dry oak hardwood left over from the living room floor, which got new hardwood a few years ago. I started out by using a 2" hole saw to cut a piece out of one of the short boards.


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## Brian Rupnow (Aug 7, 2013)

I set the cut out piece of oak up in my lathe and bored it out to 13/16" diameter, then mounted it on a stub arbor to finish sand it a bit and clean  up the outer diameter.


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## Brian Rupnow (Aug 7, 2013)

Then it was over to the milling machine to drill a 3/16" hole all the way thru and tap it 1/4"-20 unc completely through.


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## Brian Rupnow (Aug 7, 2013)

I found a 1/4"-20 bolt x 1 1/2" long, cut off the head and turned the threaded end to a point. Then I drilled a .112" diameter hole in the other end, x 1/2" deep. shoved the stripped end of a heavy piece of automotive electrical wire down the hole and crimped it with my vice grips so the wire couldn't fall out. (The other end of the electrical wire got soldered to an alligator clamp). I then turned one end of a 3/8" diameter piece of cold rolled steel to have the same approximate profile as the cm6 sparkplugs I use, and turned the other end to 1/4" and threaded it 1/4"-20, with a point similar to the point on the bolt. These threaded shanks were both given a shot of Loctite and screwed into the hardwood "donut" from opposite sides, leaving an approximate 1/16" gap between the points.


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## Brian Rupnow (Aug 7, 2013)

The silicone boot on the end of my coil wire snaps onto the side which has the CM profile on it, and the alligator clip is affixed firmly to some part of the engine to ensure a complete circuit for the high tension spark.


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## chucketn (Aug 7, 2013)

How well does it work? I could have used something like this when repairing my lawn tractor last week! Problem ended up being a plugged carb, but this would have made checking for spark easier.

Chuck


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## Brian Rupnow (Aug 7, 2013)

chucketn said:


> How well does it work? I could have used something like this when repairing my lawn tractor last week! Problem ended up being a plugged carb, but this would have made checking for spark easier.
> 
> Chuck


.

Don't know yet Chuck. I just finished it. I will post about the results  as soon as I have tried it.---Brian


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## Brian Rupnow (Aug 7, 2013)

Chuck---It works like a charm!! I just did a temporary hook up of the cdi, and yes, we have sparks.


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## tornitore45 (Aug 8, 2013)

I have one of those S&S ignition kits and for the money they seem quite effective and popular.   I asked to supply a coil with both HV terminals available and connect two spark plug in series in a wasted spark system.

The cilinder in compression require HV but the cilinder in exaust has atmospheric pressure and requires no more than what the distributor would take, about 800-1000V.


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## gus (Aug 9, 2013)

Hi Gurus,
Thanks for helping saving $$$$$ to eliminate frying the CDl which should arrive which I get home this evening.
Step one ----------hook up earth connection.
Will try out on Webbie. This weekend boat fishing and the tide looks good.


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## Art K (Aug 9, 2013)

Hi Brian,
I must admit, on a less serious note that this reminds me of my dads spark plug tester. It was one of those old automotive setups that allowed you to clean (sand blast) the plug, then screw it into the tester and see if there was a spark through a hole with a mirror. I believe you could even attach air pressure to simulate the combustion chamber. More often a clip lead attached the high voltage lead to the skeleton key hole and one stood unseen around the corner and zapped someone when they opened the door. Lots of fun was had by all with that piece of equipment.
Art


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