When to replace spark plugs?

[Knot Waiting]

Just wondering what your (iboats community) opinion is regarding the best time to replace spark plugs on a fogged engine at the start of the season: Before the engine is ran for the first time or after? The difference being what plugs burn the fogging oil off.

 

[TilliamWe]

Re: When to replace spark plugs?

Don't replace them at all. Burn off the oil and they'll be fine. Seriously, with electronic ignition and today's spark plugs, they go A LONG time before needing changed. I changed a set in my 1990 Chevy van, that had 105k miles and was 18 years old, and they were originals! Guess how much better the van ran after that? That's right, not one bit better.
My 1997 Mercruiser 5.7 had 5 year old, 300 hour spark plugs in it, that looked brand new when I changed them.
Waste of time and money, unless you actually have a problem with one of them.

That's my opinion.

 

[bruceb58]

Re: When to replace spark plugs?

I would at least pull them annually or every other year so they don't get stuck. You don't have to replace them. You can also get an idea if there is anything going wrong early...for example, if you have a steam cleaned plug!

 

[Bondo]

Re: When to replace spark plugs?

Ayuh,... I'm with Bruce,... Even my AC MR43T alloy bodied plugs get stickier if left alone to long...

Pull 'em, look things over,+ if the electrode,+ ground strap are still nice 'n square,...
Put 'em back in for another season...

 

[Mischief Managed]

Re: When to replace spark plugs?

I'm surprised that so many folks say to not replace them. I thought I was unusual in that I don't change them often. Mine have 4 seasons of use and still look fine.

 

[JustJason]

Re: When to replace spark plugs?

Per Merc its 200 hours or annually. If your plugs get boogered up even from normal wear and tear the ignition coil is going to work very hard to make those plugs spark. I dunno about you, but I don't keep spare ignition coils on my boat, And I certainly don't want to be out in a boat someplace and have the ignition coil start boiling out on me coz it's getting to hot.

 

[Fishermark]

Re: When to replace spark plugs?

I suggest "Knot Waiting" till the engine dies anyway. (Sorry, I couldn't resist. )

 

[I/O WALDO]

Re: When to replace spark plugs?

"If your plugs get boogered up even from normal wear and tear the ignition coil is going to work very hard to make those plugs spark"............................Interesting!??

 

[bruceb58]

Re: When to replace spark plugs?

"If your plugs get boogered up even from normal wear and tear the ignition coil is going to work very hard to make those plugs spark"............................Interesting!??

I take it you have issue with that statement?

 

[JustJason]

Re: When to replace spark plugs?

Yep, if you have nice clean new plugs set at the proper gap it only takes 10-15 thousand volts to fire off.
As the electrode wears, as the gap becomes bigger, as resistance increases because the plugs are covered in soot and grime it takes 30+ thousand volts to get them to fire off. Sometimes even way more than 30+K. Now the coil will do it...... for a while.
But as voltage increases so doesn't temperature, the coil is not going to be happy in the long run, and eventually it will misfire, boil out, crack, short, or just quit working.

 

[robert graham]

Re: When to replace spark plugs?

Harbor Freight Tools sells a little spark plug sand blaster for $17, mount it on the wall of your shop, hook it to your air compressor, cleans plugs like new, outboards, lawnmowers, leaf blowers, etc., probably never buy another plug. My Yamaha is a 1999 2 stroke and it's still got the original plugs in it, pretty much like new. After you sand blast them, blow off all sand with air hose. With marine spark plugs at $4 each, the little blaster pays for itself very fast and motors start and run better when plugs nice and clean. Good Luck!

 

[Aviator5]

Re: When to replace spark plugs?

The output voltage of ignition coil does not depend on condition of spark plugs. Bad sparkplugs will never destroy ignition coil.

 

[JustJason]

Re: When to replace spark plugs?

The output voltage of ignition coil does not depend on condition of spark plugs. Bad sparkplugs will never destroy ignition coil.

Hahaha... Oh yeah?

Answer me this, i'm working on this 4 cylinder engine that has a misfireing problem. I've measured my spark voltage with a KV meter. Cylinders 1 2 and 3 are fireing at 18 thousand volts, Cylinder 4 is fireing and misfireing at close to 40 thousand volts. Now remember I have a tool that measures voltage. Why is cylinder 4 needing twice voltage as compared to the other 3 cylinders?

(ps~there's a alot of reasons why that would happen, but I want to hear your answers)

 

[bruceb58]

Re: When to replace spark plugs?

The output voltage of ignition coil does not depend on condition of spark plugs. Bad sparkplugs will never destroy ignition coil.

This is the problem. If you have a plug that the gap is too wide, the voltage generated by the coil is not high enough to bridge the gap. The energy wants to go somewhere and what happens is that it can blow through its internal insulation trying to find a path to ground thus causing the coil to fail.

Same applies to bad spark plug wires, rotor and cap.

 

[Aviator5]

Re: When to replace spark plugs?

This is the problem. If you have a plug that the gap is too wide, the voltage generated by the coil is not high enough to bridge the gap. The energy wants to go somewhere and what happens is that it can blow through its internal insulation trying to find a path to ground thus causing the coil to fail.

according to that theory any transformer should destroy itself if secondary is open (no load). Ignition coil is a simple and plain autotransformer. Energy is generated only if there is a load. If there is no load - no energy generated or transformed in this case.
Increased voltage on one of the cylinders indicates that the spark plug is not firing. But to increase the voltage to normaly firing spark plug you need to increase primary, but it stays constant at 12 (14.4-14.6) volts.
Ignition coils are designed to withstand increased open circuit voltage.
Ignition coils also fail with a perfectly good spark plugs attached to them.

 

[bruceb58]

Re: When to replace spark plugs?

I understand the way you are thinking but let me ask you this. You have generated a huge magnetic field. The points now open. What do you think happens to this energy when the field suddenly colapses? It doesn't just magically go away.

 

[JustJason]

Re: When to replace spark plugs?

Increased voltage on one of the cylinders indicates that the spark plug is not firing.

Huh? If the spark plug wasn't firing, the voltage would be 0 if using a KV meter to measure. If the KV meter reads 40k, there is still 40K going through the plug wire, and it's going someplace.

Increased voltage on one of the cylinders indicates that the spark plug is not firing. But to increase the voltage to normaly firing spark plug you need to increase primary, but it stays constant at 12

Nope. The voltage will stay the same but the coil will draw more current. More current means more heat. Heat ='s Baaaaaaaaaaaaaaaaaad, as a sheep would say.

 

[bruceb58]

Re: When to replace spark plugs?

according to that theory any transformer should destroy itself if secondary is open (no load).

Only a transformer where the windings ratio of primary to secondary would step the voltage up so high that you could induce internal arcing.

 

[Aviator5]

Re: When to replace spark plugs?

0 volts would indicate that spark plug is shorted. Voltage will increase only if circuit is open, but then current will be 0A.
Current increase in primary won't increase the voltage in secondary.
This is a voltage transformer, not a current transformer.
If points are open there is no energy generated, transformed or accumulated.
And there is no energy drawn from primary either, except for the power loss in the primary.

 

[bruceb58]

Re: When to replace spark plugs?

There is huge magnetic field that is generated in the primary with the points closed. When the points open which causes this field to collapse, you get a huge current induced onto the secondary coil which produces the extreme high voltage that will hopefully end up at the spark plug. If this voltage has no place to go, it will find the closest place to ground which may be through the insulation of the coil itself.