Testing Spark Plug - and spark repair.

[pckeen]

I tried something I saw on a youtube video for testing sparkplugs on a 1958 10hp Johnson 10016 (because I've mislaid my spark tester) - basically unscrewing them and leaving them out of the cylinder head, connected to the spark plug wires, then turning over the motor. The top spark plug has visible spark, the bottom does not. However, spark was only visible when the top spark plug was either touching, or very close to the crankcase - I assume making a connection.

So two questions.

First, Is this an OK method of testing a sparkplug, or not?

Second, the spark plug wires are cracked in a couple of places, so I'm thinking that before I begin replacing coils, I should replace the wires and plugs. Am I on the right track with this.

 

[steelespike]

The plugs need to be grounded to the block or some component attached to the block.
The stator needs to be grounded some use a braided wire.
Replace the wires there are kits listed here.Must be solid core wires.

 

[bonz_d]

pckeen that is one way to check though as you would probably guess not a very good or reliable one. If you look I recently have a thread on spark here, http://forums.iboats.com/forum/engi...on-evinrude-outboards/10024200-fd-14-no-spark it is a 1960 18hp Johnson with basically the same ignition setup.

Here is also a very good video series that you should watch. He is very thorough. https://www.youtube.com/watch?v=oTN8Ag_aj-8

As you can see in my thread linked above it really had me stumped. Agree that the wires should be replaced if they show signs of deterioration or cracking. The second video will show how to test the coils.

Good luck and have fun!

 

[gm280]

PCkeen, as previously stated, YES you need to replace the spark plug wires. Any cracks on any high voltage wire is asking for trouble. Because as the cylinder is filled with a mixture of gas, oil and air, the spark gets a lot harder to jump the spark plug gap. And that forces the high voltage to go to the least resistance and those cracks become that path. So you get misfires and a very poor running engine. So replace any high voltage item that shows signs of cracks. That even goes for coils as well... Interestingly enough, if you view any ignition engine running in the dark, if there is any problems with the ignition system, you will see sparks jumping from the wires to the engine casing. And that is robbing your of engine power. Those parts need to be replaced...

 

[pckeen]

Thanks Gentlemen - I'll watch the video series and get working on replacing these items.

 

[pckeen]

What kind of a multimeter should I pick up for testing purposes?

 

[bonz_d]

Just about any will do just don't buy the cheapest one because they don't always work very well. Besides it's a good tool to have if you're going to be doing any kind of electrical work.

I've got a mid range Fluke that was about $250.00 but then I used it everyday at work. Should be able to find a decent one in the $25.00 to $50.00 range that will do most things and will last. Even the old type analog meter will work.

 

[Vic.S]

What kind of a multimeter should I pick up for testing purposes?

I always suggest an inexpensive meter, but from a reputable source.

I bought two of the ones pictured below from a well known UK electronics equipment and components supplier when they were on offer at 2 for 5 GBP.

If I wreck one or drop one in the water I have not lost a shed load of money.

I normally keep one on the boat, but Id not do that if I had bought something expensive like a Fluke!

I'd stick with a digital meter as the analog ones can be quite fragile

Worth getting one with a diode test range, which mine do, as that can be useful for testing rectifiers.

Another useful feature, which mine don't in fact have, is a continuity horn/buzzer.


Make up some longer leads with clips on the ends for what ever you buy.... Use "extra flexible" wire and clips with insulating covers.

 

[pckeen]

The Multimeter reveals the primary windings on both coils were fine, but the secondary windings were shot. So I'll be replacing both coils. As noted earlier, the spark plug wires and boots were also dirty and cracked, so I'll be replacing those as well. Is there any special kind of wire and plug boots that I should get, or does anything go?

D

 

[bonz_d]

They need to be solid core wires.

 

[oldboat1]

If coils and wires, would consider just replacing points and condensers as well -- save some grief.

 

[HighTrim]

That sort of spark test is useless really.

You need to invest in an open air gap spark tester. One you can adjust. For the OMC magneto ignition, set it to 1/4"

The reason is this. Many motors will show spark when tested like you did, but will not run, and it fools you into thinking you have a fuel delivery issue. The spark has to be able to jump the gap, under the compression in the cylinder, which you don't have when you test in open air like that. So, adding the 1/4" gap on the adjustable tester, helps mimick the compression in the cylinder, and makes it harder for the spark to jump. Real laymans type explanation, but you get the idea.

These testers are like 5 bucks, and a must have.

The primary windings in the coil, are short, and fat, and almost always good. The secondarys are long and thin, and often the problem with a failed coil. If the coil is cracked, and original, chuck it, no matter if it passes a continuity test or not.

Some coils will pass a continuity test of the primary and secondary with a standard multi meter, but still not work. That is where testing equipment like a Mercotronic comes in. It puts a load on the coil to test. Sometimes, the secondary is cracked, or severed, but just slightly touching. It will show continuity, and you think its ok. Then on the water, it will fail when it heats up, and the fractured wires separate, losing continuity. You go home and test it again, once cooled, and it tests fine. You get the idea there where you need the right equipment.

If the condensors are the red paper tops, they are original, and should be changed, especially if you don't have the ability to test them. If they have black rubber caps, they have likely been changed, and may be ok. I almost never change points, I like the originals quality better than what you get nowadays, unless the rubbing blocks are so worn you must. Simply polish them, by either a points file, or touch them against a wire wheel on a bench grinder, then set clean with brake cleaner and install. Set to 020, then dip business card or paper stock in acetone, and run that through to clean again. Your fingerprints will limit spark. Now blow off with compressed air and you are done.

When you install the wires into the coils, pull through excess wire from under mag plate, and twist the coil onto the wire. Then push back down and secure to bottom of plate.