Homemade spark tester

Mas

Mas

Lieutenant Commander
Joined
Oct 3, 2006
Messages
1,656
I've been searching for a pic of a homemade spark tester that I saw about a year ago...but I cannot find it. Some of the searches came up with one by BoatBouy, but the link is not working.

Anyone have a good pic of a homemade tester?

MAS
 
tashasdaddy

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Homemade spark tester

is this the one you were looking for. Joe Reeves Joe Reeves is offline
Vice Admiral

Join Date: Feb 2002
Location: Central West Florida
Posts: 5,903
Default Re: 1989 spark problems
Assuming anything is a mistake. Print out what I've had to say and when you get the boat back, run it thru the checks I mentioned. Here's a home made spark tester you can easily make.

Spark Tester - Home Made
(J. Reeves)

A spark tester can be made with a piece of 1x4 or 1x6, drive a couple nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:


..........X1..........X2

.................X..(grd)

..........X3..........X4
 
5150abf

5150abf

Vice Admiral
Joined
Aug 12, 2007
Messages
5,808
Re: Homemade spark tester

You can get pretty creative with stuff like that, I made one with a 3''x 1/4 bolt(in the plug boot) and a big straight screw driver grounded to the block, taped the whole deal to a piece of cardboard and shazam, a spark tester.

All you need is something to act as a plug and something metal for the spark to jump to.
 
T

tx1961whaler

Vice Admiral
Joined
May 31, 2008
Messages
5,197
Re: Homemade spark tester

HOMEMADE SPARK TESTER:
Grab the bare spark plug wire with your right hand.
Crank the motor.
With a good spark, your entire arm will go numb for 20 minutes. You may even pee yerself.
Anything less is not acceptable.
NOTE: Don't use yer left hand. That's too close to your heart..... :eek:
 
F

fishrdan

Admiral
Joined
Jan 25, 2008
Messages
6,989
Re: Homemade spark tester

Guess I'm cheap, I just use old spark plugs grounded to the block.

I suppose you could make a multi-tester from a hand full of old plugs, board, plumbing tape (metal strap), screws wire and an alligator clip. Screw plugs to board with plumbing tape, attach grounding wire and alligator clip, gap plugs to what you want. Won't be pretty,, but it will be pretty cheap:D
 
iwombat

iwombat

Captain
Joined
Jul 12, 2006
Messages
3,767
Re: Homemade spark tester

Old spark plugs grounded to the block will not give a proper spark test.
 
W

wilde1j

Vice Admiral
Joined
Apr 15, 2002
Messages
5,964
Re: Homemade spark tester

You need to be able to adjust the gap between 3/8" and 1/2" and each hot needs to have a needle point (nails ground to a fine point work well ... old spark plugs are not going to be any good for this). i.e. X1 ... Xn.
 
Mas

Mas

Lieutenant Commander
Joined
Oct 3, 2006
Messages
1,656
Re: Homemade spark tester

Thanks guys, I'll give it a go! No real urgency, just tinkering & trying to stay busy waiting for it to warm up!

MAS
 
E

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: Homemade spark tester

Someone posted this design which I thought was easy to make.
 

Attachments

  • spark_tester_2.jpg
    spark_tester_2.jpg
    37.5 KB · Views: 23
F

fishrdan

Admiral
Joined
Jan 25, 2008
Messages
6,989
Re: Homemade spark tester

wilde1j said:
You need to be able to adjust the gap between 3/8" and 1/2" and each hot needs to have a needle point (nails ground to a fine point work well ... old spark plugs are not going to be any good for this). i.e. X1 ... Xn.
Click to expand...

Ahhh, I see, you guys are talking about seeing how far the spark will jump, just not if there is spark. My mistake :D
 
james williams

james williams

Petty Officer 2nd Class
Joined
Jul 22, 2006
Messages
105
Re: Homemade spark tester

tx1961whaler said:
HOMEMADE SPARK TESTER:
Grab the bare spark plug wire with your right hand.
Crank the motor.
With a good spark, your entire arm will go numb for 20 minutes. You may even pee yerself.
Anything less is not acceptable.
NOTE: Don't use yer left hand. That's too close to your heart..... :eek:
Click to expand...
I`ve used that one for fifty year.I`ve never predited one wrong yet.
 
jay_merrill

jay_merrill

Vice Admiral
Joined
Dec 5, 2007
Messages
5,653
Re: Homemade spark tester

iwombat said:
Old spark plugs grounded to the block will not give a proper spark test.
Click to expand...


As long as they are functional, old spark plugs, why not? After all, thats what the motor needs to spark!

BTW, spark testers can be purchased at an auto parts store for a few dollars. With that in mind, why bother making one?
 
Tim Frank

Tim Frank

Vice Admiral
Joined
Jul 29, 2008
Messages
5,346
Re: Homemade spark tester

jay_merrill said:
As long as they are functional, old spark plugs, why not? After all, thats what the motor needs to spark!

BTW, spark testers can be purchased at an auto parts store for a few dollars. With that in mind, why bother making one?
Click to expand...

I was in your camp (and had always done that) until I started reading these forums.
You need to evaluate not just whether there is spark, but also the quality of it.
Suddenly the spark tester makes perfect sense because it is so easy to adjust and actually get a QUANTiTATIVE read on the situation ~ i.e. do you have a spark AND will it jump 3/8" gap (or whatever).

There are some great homemade ones out there (and i belong to an old car forum that also has a bunch of excellent designs in posts) but NAPA sells a pretty good one for under $10- ; although I am frequently embarrassingly frugal with some things, that seemed too reasonable to spend time cobbling one together myself.
 
iwombat

iwombat

Captain
Joined
Jul 12, 2006
Messages
3,767
Re: Homemade spark tester

Right you are. Spark jumping a spark plug gap outside the cylinder grounded to the block does not simulate firing conditions inside the cylinder under load. Jumping an air gap of between 1/4" and 1/2", depending on ignition systems, does.
 
J

jonesg

Admiral
Joined
Feb 22, 2008
Messages
7,198
Re: Homemade spark tester

Just to beat this subject to death...

A spark will jump more readily outside the cylinder simply because there is no compression, because under cylinder pressure the spark resists jumping.

A weak coil can produce a healthy spark on a plug outside the cylinder but fail to spark when installed in the engine.

hence the need to see if it jumps 7/16th gap when not under load.
 
jay_merrill

jay_merrill

Vice Admiral
Joined
Dec 5, 2007
Messages
5,653
Re: Homemade spark tester

jonesg said:
Just to beat this subject to death...

A weak coil can produce a healthy spark on a plug outside the cylinder but fail to spark when installed in the engine.
Click to expand...

That's the info I was looking for - that makes sense. I do use a spark tester and even keep one in the tool kit on my boat. I would also say that it really doesn't make sense not to use one, because they are cheap and easier to use than a plug.
 
You must log in or register to reply here.
Top