Compression Testing

[dave-bernard]

Same here.

[jeff-register]

The magneto creates energy & does not go away. Needs to be discharged before it finds the easiest path thru ground….thru the windings & mag plate. It WILL blow tiny holes thru the coil to ground opening secondary windings causing an open or carbon connection.
Also when checking compression I would say around 20% difference between cylinders is out of spec & needs attention.

[Samuel Phelps]

I heard about grounding the plugs and I started doing that . What is the chance of fuel fumes coming out of the open cylinders causing a boom ?
That’s always sort of freaks me out .. wrapping a wire around the plug bases then grounding the wire is how I do it . I
Am I doing it correctly ?

[JOHN HOLBIK]

I personally dont totaly agree that a magneto ignition must have the wires grounded I know electricity will take the path of least resistance but when the gap to ground is beyond the capacity of the coil the electricity is contained in the mag as the potential to ground is beyond the coils capacity. I have tested motors for 50 years pulling off spark plug wires etc.We ran a fishing resort for 49 years and probably hundreds of motors came home on one cylinder because the other was fouled. I never ever saw any electrical damage as a result of this.
With electronic ignitions there is a greater chance for grounding issues as the voltage is much higher and the sensitivity of electronic components

[frankr]

My opinion on this:

Not grounding the wires CAN bust through the insulation if the available spark is strong enough, AND the insulation is weak or compromised. But the chances of this happening are sort of iffy and the coils probably are crap anyhow.

Chances of a fire: YES, YES, YES. The only reason I’m sitting here writing this is because I was standing to one side. And the Grace of God. See, I had this electric start V4 motor that wouldn’t start, mounted on the boat, and was about to check for spark by cranking it using a jumper switch to run the starter. Plugs were out. Open spark checker was on plug wires. What I didn’t know was that the motor was badly flooded. As soon as I hit that start jumper switch and the motor started to spin over, that flooding gas came blasting out of the spark plug holes an the spark checker ignited it. A column of fire came shooting out about 10 feet. If I had been standing one foot closer in line, that burning gas would have hit me and I would have been on fire. Another stroke of luck was that I didn’t set the shop on fire.

Be safe, guys. And think.

[fleetwin]

I remember my first job….For some reason, I was checking spark or cranking the 4hp over with the plugs out in the test tank…And then puufff, the thing was on fire….The extinguisher was on the other side of the shop, so I unclamped the little engine and dunked it in the test tank! Fortunately, it didn’t get wet under the flywheel, so just cranked the water out and it started right up….Often wondered if anyone else noticed, I think I was alone in the shop….

[Buccaneer]

I’ve told this story before, but I’ll amuse myself once more…..
With all this “talk” of outboards “self emmolating”, I’m starting having “flashbacks”
when I was a young teenager, circa 1969, starting up
the 3 hp Buccaneer at the dock. Priming said motor ends up with some gas
running down the inside of the cowling. Perhaps Gale didn’t think ahead that
in a mere 15 years, their spark plug wire might be worn, or have leakage.
Thank the Lord for leaky wooden boats and a handy bailing bucket………
that was the first time it happened. I know you’re thinking there shouldn’t be
a second time, but at 13 years or so old, outboard maintenance wasn’t a priority…
if it started, you were good to go!
The bailing bucket didn’t do the trick the second time, and after bailing water
out of the lake wasn’t “doing it”, a panic set in. I probably should have run at
this point, but bravery / stupidity set in, and I un-clamped the motor from the transom
and threw it in the lake. After fire danced on the water for about 15 seconds and
went out, I realized I was going to live, and I started feeling better, until I looked up
at the house and seen my brother looking out the picture window laughing his
hinney off.
I can’t remember if the spark plug wire ever did get replaced on the Buccaneer.
It’s up in the rafters, awaiting new adventures.

Prepare to be boarded!

[garry-in-michigan]

With age those old Packard 440 wires tended to crack where they exited the clamp under the magneto base. Sounds like a good time to install new ignition wires.

[Author]

Posts