Do you faithfully check sparkplug gap?

[klickitatsacket]

sorry Russ I took the information I was given and tried it and it worked so his explanation was good enough for me. Maybe the travel thing was wrong but I know from experience that changing the gap changes the characturistics of the engines performance.

 

[Simonizer]

Hi Eric,

I understand that you can alter the timing of the combustion event with the plug gap, what I don`t seem to grasp is how closing the plug gap is making the spark cover the distance of the gap appreciably faster or slower, or in any meaningful way.

What I believe is happening is that the flame propagation rate is being changed proportionate to the spark energy.

If we have any SAE engineers reading who would like to explain the error of my thinking, I`d like to hear the logic. Otherwise I guess that we are relegated to debating this as layman. I am curious to hear theories and opinions.

Thanks Eric for relating your experience and observations.

Russ

You are absolutely correct Jokers. BTW it's 186262 miles per second. In Canada we use 2.9979*10^8 m/s. Ha ha. Incidentally these velocities are in a vacuum. Light travels slower through different mediums proportional to the refractive index of that material. I realize this is COMPLETELY irrelevant to our topic but I had a few beers and felt like rambling. Cheers.

 

[Simonizer]

As the magnetic field collapses in the coil the voltage builds rapidly in the secondary......but not at nearly the speed of light. Once this voltage gets high enough to 'jump the gap' in the spark plug the electrons then move at the speed of light and ignite the mixture in the cylinder.

If a dual trace oscilloscope were put on the primary and secondary the timing changes involved could graphed with various gap settings.

This is my speculation purely from an electronics point of view as I'm no engine man.

Dan

You would have to have an inductive pick-up for the secondary side. A have a 2-channel Tektronics scope (400MHz) and it would HATE a 20 Kv input ha ha.

 

[jokers]

sorry Russ I took the information I was given and tried it and it worked so his explanation was good enough for me. Maybe the travel thing was wrong but I know from experience that changing the gap changes the characturistics of the engines performance.

No sweat Dean, sorry if I made you feel like you`re taking the heat on this. You may have noticed by now that some small statement or remark will catch my attention and I will try to get a discussion going. Sometimes for a better understanding of the topic, sometimes for sh!ts and grins.

Thanks Simonizer and TreeCo for jumping onboard!

Russ

 

[scottr]

Load & Voltage

Dan , the lower load of a narrower spark gap may not allow the secondary to completely saturate . Maybe Dean had increased the compression ratio to the point that the higher compression required more voltage than the coil could produce at the specified gap . I wonder how long the center electrode will last at a .010" gap . Simon , if you don't have a high voltage probe you can make a voltage divider with resistors .

 

[asb151]

I seldom gap the plug. About all I do is pull the plug occasionally and make sure the electrode is still physically there.

Seriously though I have never had a problem. Even when I replace an old worn plug with a new one I don't notice any difference in how the saw actually cuts. Perhaps I would see it on a tachometer but its not very noticeable to me in cutting speed.

Maybe that’s just me.

 

[NevadaWalrus]

I doubt timing is altered much if at all by changing plug gaps. What is effecting engine operation is a wider gap requires a hotter spark to jump that gap. That is after all the concern of overworking the coil and causing an early failure of the coil. The hotter spark required by a wider plug gap causes the coil to work much harder to produce that hotter spark.

A hotter spark (higher voltage) will make an engine run better, faster which is why racing engines use high output ignition systems. The problem is achieving the balance between higher engine temps, ignition life and performance.

 

[buck futter]

I must challenge the the theory of a larger gap plug ruining or even requiring more output from the coil or ignition module. The plug will be conducting less with a wider gap plug, It takes a higher voltage, true. however the larger gap is a larger resistve value until the arc has begun at which time the resistance drops to next to nothing. I believe that the arc is extinguished by the explosion.

When the gap is shorter the arc happens quicker because it needs a lower voltage to overcome the resistance of the smaller gap. So this and the shorter distance I believe will change the timing. If a lower voltage is needed then the spark should happen sooner and the same amount of energy is dispersed at a lower voltage. Same joules @ lower voltage = Higher current which means more heat in your ignition system. Although this may be a wider arc it is not as long, which way provides better ignition?

Also for what its worth a resistor divider will work although it has two major downfalls for high voltage detection. one is that puting any resistance in parallel will lower the impedance of the circuit to less than half of the original impedance. It will certainly gum up the works and give you a faulty reading. the other is safety minded if one of your resistors shorts out the remaining resistors must hold off the same voltage this can mess up your readings but also they may all fail and become a dead short. Lets say all hell broke loose and your holding on to your trusty tektronics scope you my friend may have the extreme pleasure of being part of the current path.

Now more than likely the current and voltage pulse are not in sync due to inductive and capacitive reactance. so we must look at both pulses. The current pulse with a properly stood off current coil (donut) and a capacitor divider for the voltage pulse.

Now the question was what time is it and I'm telling you guys how to make a watch.

Wake up here is my cliffs notes version, I believe larger gap for longer ignition life and timing may be affected by plug gap.

So whats best?
I haven't a clue I just set my plugs to twenty thousands and cut wood.

Lucky

 

[Ryan Willock]

I must say that is one thing I do not worry about! Takes too much time away from cutting timber!LOL

 

[scottr]

Voltage divider

Lucky001 , if you properly choose the values of the voltage divider resistors the equivilent resistance will not be less than one half the spark gap resistance . Your statement of same joules @ lower voltage = Higher current might be assuming that the secondary field is saturated at the lower voltage discharge . I haven't ever seen a precision carbon resistor short . Maybe Tony Snyder will give us some information as I remember him saying that he designed saw ignition systems . I don't remember Dean mentioning if his ignition was a points type , breakerless type , or a breakerless capacitive discharge type . It could make a difference in the rise time of the secondary voltage .

 

[buck futter]

The enamel coating on enameled magnet wire that is wound in coils contains varying degrees of blisters, out of roundness, pinholes and about a hundred other possible blemishes to the surface. The voltage from any single turn of wire to an adjacent turn would never exceed the normal 400 -800 volt breakdown of the enamel, but where pinholes exist, the breakdown could be as low as 100 volts.

Of course you could be one of the lucky ones who has a coil that contains a stretch of heavy build, blemish free enameled wire. In that case you can run it for years with as large a gap as you want with no damage.

Isn't this what potting is for?

If there is a blemish or suspected blemish it should be covered with glyptol. However I can't imagine this is a huge problem or coils would fail more often, I would love to know how the manufacturers have overcome any problems.

I don't know what they do for chainsaws i would think that potting would be a great idea both for its electrical insulating properties as well as it ability to dampen the vibration also potting is well known for its ability to wick away heat. Heat for my experience is most often the killer for the enamel on magnet wire heat is generated by current of course, and even if one or two coils short out it will most likely not be the end of the world. depending of course on the number of turns. The voltage of the spark is regulated by the gap. bigger gap bigger voltage, smaller gap smaller voltage. Of course at both extreme ends of the gap size it will cause problems with the ignition module and may be limited by other factors. I guess the whole point I was trying to make duty cycle is a key factor. I peak vs. I average.

Lucky

 

[pallis]

Man, you guys sure do know how to make me feel stupid. This reminds me of some conversations I've had with my son the physics major. I have to remind him that I'm a math for the liberal arts kind of guy. That means I gap my plugs because I know they are supposed to be gapped, and I don't want to stress my brain with the details of why. Now I see that I'm woefully ill equipped to decide whether or not I should gap my plugs. From now on, I'm going to take my saws over to Los Alamos, and let those guys do it.

 

[JohnL]

I gap them when putting in a new one, or when reusing an old one in a saw bought from someone else. Mostly my saws call for 0.025", usually the existing gap is wider. I figure the manufacturer spent enough time to figure out what worked best, and trust that in a stock saw.

I would have thought that a smaller gap would take less voltage to start the arc, so that if voltage is building, it would fire sooner. With a wider gap, takes a little longer to build the required voltage to start to arc, making the spark a little later.

I like hearing about the coil manufacturing stuff.

 

[BlueRidgeMark]

I guess the whole point I was trying to make duty cycle is a key factor. I peak vs. I average.

A key factor, but not the only one. If you have a (relatively) long time between voltage pulses, but those pulses are extremely high, you can have arcing (insulation failure) even though your total power (the area under the curve) is well within limits.


Interesting discussion. Whoda thunk a bunch of chainsaw jockeys would be found discussing the finer points of impedance, voltage rise, etc.?


Cool!


Shall we get into the discussion (debate) of how a spark actually creates ignition in an air/fuel mixture?

 

[16gauge]

Very Interesting Thread

The technical stuff here reminded me of a painful experience 33+ years ago. To get through Navy Electronics Technician training we had to build a "superheterodyne" radio receiver. I did OK with the high voltage power supply...it tested out to specs...but forgot to discharge it before connecting it to the receiver section. An arc passed through the meaty part of my thumb and thumbnail and then ...really bad sting and worse smell. That was only 180 volts dc...not 20 to 30K.

Please don't try the proposed test...the tektronics can be replaced but I enjoy these posts too much to think about losing a contributer to this site over an unneccessary experiment. Sorry if this seems like preaching but I've had other electrical shocks including a "holding shock" where you can't let go...the bottom line is...gap your plugs any way you want but keep your hands off the high voltage stuff unless you really really know what you are doing.

Phil

 

[scotchguy]

Shocking!

When the gap is shorter the arc happens quicker because it needs a lower voltage to overcome the resistance of the smaller gap. So this and the shorter distance I believe will change the timing. If a lower voltage is needed then the spark should happen sooner and the same amount of energy is dispersed at a lower voltage.

Lucky

Exactly right. Think about what happens when you are flying a kite and it gets tangled in a 4000V power line ... nothing. However, when it gets tangled in the 100,000V line, the voltage overcomes the resistance of the string creating an arc. The ark is a plasma in which the molecules of air surrounding the string have been stripped of their electrons. The resistance of the plasma is almost zero and the power moves from the electric cable, down the arc in a bolt of lightning, reaching the ground throught your outstretched arm.

Sorry to be picky on the subject, but electrons have mass and therefore can not move at the speed of light. I think the mass of the electron is why the utility companies supply us with AC not DC. In AC supplies the electrons shimmy back and forward in the wire.

 

[scotchguy]

Three inches per hour!!!!!!!

I just did a Goodle search and learned far more than I ever wanted about the speed of electrons in a copper wire.

http://www.amasci.com/miscon/speed.html

Apparently, if you turn on a domestic lamp you cause the electrons in the wire to flow at 3 inches per hour!

The energy of course travels a lot faster ... almost the speed of light, in fact.

 

[klickitatsacket]

Hey Russ, I am glad you picked on my statement. I now understand why it works. I have no problems being called out on a statement, I like to learn and this whole thread has been a blessing.

 

[Al Smith]

Well It appears there are several theories about the speed of electrical energy.I've never heard of measuring current with an O-scope.I also might add that I've never heard of some of those theories.I would have thought that after being a navy submarine sonar tech and then an electrician for 34 years that I would have.Continue on if you please,I'm always eager to learn.

 

[scottr]

Tektronics Current Probe

Well It appears there are several theories about the speed of electrical energy.I've never heard of measuring current with an O-scope.I also might add that I've never heard of some of those theories.I would have thought that after being a navy submarine sonar tech and then an electrician for 34 years that I would have.Continue on if you please,I'm always eager to learn.

Al , check this out . http://www.tektronics.co.kr/product/page/Current_Probe.asp