spark plug question

[man-of-war]

I was running the 1980 454 bb 7.4L on NGK R5673-6 with a .035 gap, my plugs were always wet with gas, not to mention the gas in crankcase problem. I was reading some of the posts on this forum about spark plugs and found that BR6FS NGK are used on these big engines. I bought a set of these plugs today and gapped them to .040. Is this gap correct? I ran the engine for about 15 min in the driveway and was so pleased not to see any gas on the plugs today. I hope this is the end of the gas in crankcase problem. THANKS

 

[rbezdon]

Re: spark plug question

I can not see how changing the plugs can stop the gas in the crank case issue. I sure hope your diagnosis is right cause gas in the oil can result in the worst scenarios imaginable.

 

[man-of-war]

Re: spark plug question

at this point and time,less gas on or in any thing is good. would a .40 gap damage the pistion or should i re gap the plugs to .35 .....THANKS

 

[rbezdon]

Re: spark plug question

No, the .040 gap wont damage the piston but the change in timing may not be good. Gap can effect timing to a certain degree. It is recommended you stick with the OEM recommended gap. Gap size will not effect the amount of gas on the plugs, in the cylinder or any where else. The gas is coming from the fuel delivery system some where, not effected by the spark plugs or the gap. Check your carb and fuel pump. Most common reason for gas in the oil is a bad fuel pump or a stuck float in the carb.

 

[man-of-war]

Re: spark plug question

Thanks for the info vatter41,I dont know what the OEM recommended gap is.On the NGK site they said these plugs are gap to .40 .My engine builder sais to use .35 gap,ill re gap them back to the .35 to be on the safe side...... THANKS

 

[Bondo]

Re: spark plug question

Originally posted by man-of-war:<br /> Thanks for the info vatter41,I dont know what the OEM recommended gap is.On the NGK site they said these plugs are gap to .40 .My engine builder sais to use .35 gap,ill re gap them back to the .35 to be on the safe side...... THANKS

I Still can't see where changing your Sparkplugs are going to Fix a Fuel Issue,...............<br /><br />Either, Your Carb.(My 1st Guess), or your Fuel Pump is Broken, Bad, In need of a Rebuild, or otherwise AFU........<br />

I hope this is the end of the gas in crankcase problem.

No Way,........<br />You haven't Fixed AnyThing........<br /><br />BTW,....... Your engine Calls for AC MR43T sparkplugs...........<br />You might want to call your Engine Builder back,+ have him start building you Another motor,......<br />This 1 Isn't going to last very long...........

 

[ron7000]

Re: spark plug question

Originally posted by vatter41:<br /> No, the .040 gap wont damage the piston but the change in timing may not be good. Gap can effect timing to a certain degree.

sorry but i have to ask, how can spark plug gap affect ignition timing?

 

[rbezdon]

Re: spark plug question

It is a bit complex but the long and the short of it is that the increased gap requires a higher voltage to arc across the gap. This causes it to takes a very slightly longer time for the ignition system to build up to the spark voltage. As I understand it, the gap also effects the size of the ignited burn changing the way the burn propogates through the cylinder. Since I am not an expert and the EOMs who design these systems are, I figure I cant go wrong following their recommendations. They are there for a reason.

 

[ron7000]

Re: spark plug question

you don't remember where you came across that info do you?<br /><br />It's completely false.<br /><br />when the coil neg connects to ground, the magnetic field in the coil collapses and creates the power, at a certain voltage, which travels thru distributor cap to spark plug. Changing plug gap does not effect when the coil connects to ground to create every spark. Nor does it change the speed at which the electrical energy travels from the coil, which is the speed of light.

 

[Bondo]

Re: spark plug question

when the coil neg connects to ground, the magnetic field in the coil collapses and creates the power, at a certain voltage, which travels thru distributor cap to spark plug. Changing plug gap does not effect when the coil connects to ground to create every spark. Nor does it change the speed at which the electrical energy travels from the coil, which is the speed of light. <br />

That's Very True,...........................<br /><br />But,...... We're not talking about a Very Long Time here,.........<br />And,.......... If that Energy has to travel 0.005"s Farther ,.........<br /><br /> It Takes Longer ................. <br /><br />That will effectively Retard the Timing,..........<br /><br /><br />Of Course,............... None of this changes the fact that it's your Fuel System, that Needs the Attention.................

 

[Scaaty]

Re: spark plug question

I just love how gaps in spark plugs solve crankcase gas probs...............and start arguments! LOL

 

[ron7000]

Re: spark plug question

bondo, are you agreeing with the plug gap affects timing idea or being sarcastic? I can't tell.

 

[KRS]

Re: spark plug question

Originally posted by ron7000:<br /> you don't remember where you came across that info do you?<br /><br />It's completely false.<br /><br />when the coil neg connects to ground, the magnetic field in the coil collapses and creates the power, at a certain voltage, which travels thru distributor cap to spark plug. Changing plug gap does not effect when the coil connects to ground to create every spark. Nor does it change the speed at which the electrical energy travels from the coil, which is the speed of light.

No, it doesn't change when the coil field collapses... but that's not what ignites the fuel is it. When the spark plug discharges, that's when fuel ignites. If it is slower to discharge (longer distace to electrode) then yes, I can see that it would change timing because the spark is happening later.<br /><br />HOWEVER... it's miniscule, probably not even readable, but the premise is correct.

 

[Bondo]

Re: spark plug question

Originally posted by ron7000:<br /> bondo, are you agreeing with the plug gap affects timing idea or being sarcastic? I can't tell.

I'm in Total Agreement,...............<br />And Being Sarcastic..................... <br /><br />It's like the Computer,.............<br /><br />We're talking about Unmeasurable Time,................<br />But,......<br />It Adds Up,... And,.. It's Simple Physics,...... If it Travels Farther,............ It Takes Longer............

 

[ron7000]

Re: spark plug question

If it is slower to discharge (longer distace to electrode) then yes, I can see that it would change timing because the spark is happening later.

and so back to the original point of gap affecting timing, are you guys saying if I open spark plug gap, say from 0.030" to 0.065", I have to worry about my ignition timing?

 

[Buttanic]

Re: spark plug question

No, the change would be so small that it would probably take some type of highly accurate test equiptment that would cost tens of thousands of dollars to determine it. Worry more about if your ignition is capable of producing enough voltage to jump the .060 gap.

 

[KRS]

Re: spark plug question

So absolutely miniscule, it isn't even readable.

 

[rbezdon]

Re: spark plug question

Guys, the way the ignition works in a points type system is that at the instant the points open, the inductive energy stored in the coil tries to force current to keep flowing even though the circuit has been broken. This causes a rapid collapse of the magnetic field in the coil and a corresponding rapid rise in the coil voltage. This would be nearly instant if it were not for the condenser (actually better known in electronics as a capacitor). The capacitor creates a current path across the point gap to limit the rate of rise of the voltage. Since the rate of rise is finite, it takes a specific amount of time for the voltage to rise. At larger spark gaps it takes larger voltages to arc across the gap. Since the rate of rise is finite, it takes, admittedly VERY small amounts of time but none the less more time, to acheive the higher voltages needed to arc the larger gap. I suspect at particularly low enbgine speeds this effect on timing is very small. At very high rpm it may be different. I am certain of the electronics side of this as this is basically what I do for a living, design inductive switching circuits. In fact Ron, your statements about the speed of the electricity is correct AFTER the current flows. In fact, there is NO current flowing until the voltage potential exceeds the break down voltage of the spark gap. It is clear that you have not got a complete understanding of the operation of the complete gnition circuit including all of the elements and their function. On the other hand as I said in my earlier post, the gap also effects the propagation of the burn and I am also certain this effects the way the burn develops and the time it takes but I am not a physics guy, I am an electronics guy and there for I can not say with much certainty what the absolute effects are. I stand by the argument that the designers of the engine system recommend certain materials, fuels, adjustments and settings etc to get the best perfomance and life from an engine there for it is best to follow their recommendations.

 

[man-of-war]

Re: spark plug question

hi all, im geting the engine installed tomorrow,and had a question about what spark plug i should use.the NGK BR6FS, IS THIS PLUG TO HOT FOR THE ENGINE ? the AC MR43T is this an equivilant of NGK BR6FS. could some one recommend the right plug for this engine and gap. i dont wana blow this one up again......THANKS