Post by rudycon on Feb 25, 2014 11:00:29 GMT -5
"What? Whaddya mean my spark plug is obsolete?! What am I supposed to do now? Are you SURE this is the right plug to replace my obsolete plug?" yeah. It happens. Maybe the kid at the parts counter hands you some spark plugs that SHOULD work in your application, but how do you know it is the right plug? Here are some ideas based on my latest work with my Studebkaer champ 6 flathead. No. It isn't a GoDevil, I don't have one, but the designs are similar.
Pickin' plugs:
First of all, it has to fit in the hole. "The beauty of standards is that there are so many to choose from" -My friend Mark
My Studebaker champ6 engine? 14mm plugs. That's right; the metric system on a decidedly American engine! Don't ask me why almost all spark plugs use metric threads. 14mm 1.25pitch threads. Very common even today. Get a plug that fits in the hole. The other aspect of plug size is the base of the plug. 2 styles. Gasket and conical seat. Easy to tell what you need there, just look at the hole and decide if it is flat or cone shaped. Us flathead guys? 99% will want a gasketed plug.
Next up, pick a spark plug REACH. Measure the thickness of the threads in the hole. I betcha it lines up on something nice and even, like 3/4" on my Studebaker champion's cast iron head. This is the plug's REACH. You want the bottom of the plug body flush with the combustion chamber. Why? Fewer hot spots in the combustion chamber. Threads on the tapped hole in the head and threads on the plug are nice sharp points that can stay glowing hot after combustion. These hot points can light off the intake charge before the spark actually occurs. This is pre-ignition and it is really hard on the engine. Everything takes a beating from ring lands to crank bearings.
If you find you had short reach plugs in there, you will find a bunch of carbon built up on the threads where the plug's threads didn't cover the hole. There is a spark plug thread chaser tool that is like a tap, but less aggressive, that you can grease up and crank into the holes by hand to clean the carbon build up off the threads. I grease the tool to try to pick up as much junk as possible on the tool so it doesn't fall into the engine. A loose piece of carbon in the engine has a funny habit of sticking to the spark plug and fouling it out right after you put in that fresh plug! I also use the shop vac to try to get anything I can out of the plug hole. Crank the engine around by hand until an exhaust valve is open for best results. If you open an intake valve, be careful! You are sucking air through the carb and you might be getting that air/fuel mix all the way to the shopvac's sparking motor! BOOM! THINK my friends. THINK.
Ever have a lot of trouble removing plugs from a head? They start to back out, but get tight? There is a chance that the plug reach was too long for the head and the end of the plug was hanging out in the combustion chamber! The exposed threads on the end of the plug have carbon built up on them or chemical oxidation. Tough to crank that through the head. Be patient. little out, back in little out back in. Chances are you'll get it out without wrecking the head or snapping off the plug.
Pick a heat range.
Summary: If you have no idea where to start picking a heat range, error on the cold side to prevent engine damage. Replacing a fouled plug is easier than replacing a holed piston.
Hot or cold plug? Why do I care?
When selecting a heat range for a spark plug for your engine the way you are running it, the goal is to get a plug that runs hot enough to prevent fouling, but stays cool enough to prevent pre-ignition. This way you get long reliable service life for both plugs and engines.
You can't tune an engine with different plugs. Too rich will still run too rich with different plugs. You chose plugs to match the engine running conditions, so tune it up first before you start trying different heat range plugs.
What you are looking for is a grey plug center electrode. White = plug running too hot. A glowing hot plug tip can light off your mixture way too soon. Pre-ignition. This is really hard on your engine.
Black plug is too cold. It can't get hot enough to burn off deposits on the plug. Build up enough black stuff on the plug and it will rob or mask your spark and maybe even short out the gap between the electrode and the ground strap. That is a fouled plug.
Grey is just right. They used to say light brown/tan is right, but I think that is the color we used to get with methyl ethyl lead. I just don't see it anymore. *shrugs*
Why does one heat range plug run hot and another runs cold? It has to do with how much of the center insulator is in contact with the plug body. The more contact area, the more heat it can sink from the center electrode to the cylinder head and the colder the plug stays. Hence...a "cold" plug.
Different plug vendors use different hot-cold numbering systems. Champion and Autolite is like a thermometer. Higher numbers are hotter plugs. NGK is the opposite! The hottest NGK is a 2 and the coldest is a 12. Sneaky, eh?
Our low compression, low rpm, maybe a little more worn out oily engines might want a plug towards the hot side of normal to keep from fouling. Just check'em to make sure you are not white hot. That pre-ignition is mighty hard on ring lands.
There are many factors that affect plug temps. Mixture, RPM, compression ratio...lots of stuff. So many different variables that all come down to one thing. Getting a plug that is hot enough to not foul and cold enough to not cause pre-ignition in the conditions you are running it. So go on your test loop run, come back and pull a plug. Hopefully, you'll find you have the right plug for the job already in there.
Gap: Gotta 6 volt? bet your gap is about .025" Gotta high zoot 12volt ignition system? Bet you run a bigger gap like .030". I'll stick to the Studebaker book which runs from .025 to .028" depending on the book. Sure when you pull a plug and test for spark she'll throw a good 3/8" spark, but that won't happen under the compression inside the engine. You want as much gap as your coil will jump *reliably* in the engine to increase the chance of lighting off the charge.
Plug design/manufacturer:
Ha. You are on your own here. I'm sticking with a decidedly low tech, high quality, spark plug like the standard NGK or Autolite plugs for my Champion 6 flathead engine.
No need for long life platinum, or iridium on my Willys. The plugs are easy to change on the champ 6 anyway.
I don't feel the need for multiple ground straps, double or triple split ground straps or cut back ground straps.
I don't need ice cold race plugs in this low compression, low RPM engine. (NGK's race plugs have the SAME technology as the standard plugs, just colder heat range!)
I still run points and I don't have a radio so I don't even need resistance plugs to combat Radio Frequency interference.
How I picked plugs for my engine: The "book" calls for a long gone Champion J7. A 3/8 reach plug! The Military guys find short reach plugs for the "weasel" engine (same as my champ 6) in their field manuals too. But my Dad the Mustang racecar guy, my own experience, and almost every flathead post I can find says never pocket a spark plug. (plugs that don't reach the combustion chamber). OK. MAYBE the nitrous oxide guys and methanol racers want to control the flame front, but I dunno. As long as the valve doesn't hit the plug, we'll be OK. I have at least .125" before the valve hits with standard 3/4" reach plugs. Plus, a pocketed plug is a foul-a-matic because it never sees the high velocity hot escaping exhaust gasses that help burn off deposits on the plug. The plugs I pulled out were 7/16th reach extended nose made in USA Champion plugs. closer to the combustion chamber but not in it and not the "right" plug either. They were pretty well coated in black carbon. I'm going to go against internet wisdom (rhetoric?) here and go with plugs with a reach that matches the heads. So far, so good. runs pretty well.
NGK plug decoder chart link
www.sparkplugs.co.uk/pages/technical/NGK-spark-plug-code.htm
plug heat range chart for some vendors:
www.autolitesparkplugs.com/learning-center/article/225/heat-range-conversion-chart
Break it down:
Champ 6 has 14mm plug holes. That's a "B" on the NGK chart.
Champ 6 is a low performance engine, I'll start with a normal heat range. that's a "7" or "8" on the NGK scale.
Champ 6 stock head is a 3/4" reach head with a flat gasket surface. that's an "E" on the NGK chart.
Champ 6 is a stock engine without special needs. A standard electrode is just fine. That is an "S" on the NGK chart.
so I want an NGK, B7ES spark plug. Down to the car parts store in town and sure enough, they've got 'em on the shelf!
Pickin' plugs:
First of all, it has to fit in the hole. "The beauty of standards is that there are so many to choose from" -My friend Mark
My Studebaker champ6 engine? 14mm plugs. That's right; the metric system on a decidedly American engine! Don't ask me why almost all spark plugs use metric threads. 14mm 1.25pitch threads. Very common even today. Get a plug that fits in the hole. The other aspect of plug size is the base of the plug. 2 styles. Gasket and conical seat. Easy to tell what you need there, just look at the hole and decide if it is flat or cone shaped. Us flathead guys? 99% will want a gasketed plug.
Next up, pick a spark plug REACH. Measure the thickness of the threads in the hole. I betcha it lines up on something nice and even, like 3/4" on my Studebaker champion's cast iron head. This is the plug's REACH. You want the bottom of the plug body flush with the combustion chamber. Why? Fewer hot spots in the combustion chamber. Threads on the tapped hole in the head and threads on the plug are nice sharp points that can stay glowing hot after combustion. These hot points can light off the intake charge before the spark actually occurs. This is pre-ignition and it is really hard on the engine. Everything takes a beating from ring lands to crank bearings.
If you find you had short reach plugs in there, you will find a bunch of carbon built up on the threads where the plug's threads didn't cover the hole. There is a spark plug thread chaser tool that is like a tap, but less aggressive, that you can grease up and crank into the holes by hand to clean the carbon build up off the threads. I grease the tool to try to pick up as much junk as possible on the tool so it doesn't fall into the engine. A loose piece of carbon in the engine has a funny habit of sticking to the spark plug and fouling it out right after you put in that fresh plug! I also use the shop vac to try to get anything I can out of the plug hole. Crank the engine around by hand until an exhaust valve is open for best results. If you open an intake valve, be careful! You are sucking air through the carb and you might be getting that air/fuel mix all the way to the shopvac's sparking motor! BOOM! THINK my friends. THINK.
Ever have a lot of trouble removing plugs from a head? They start to back out, but get tight? There is a chance that the plug reach was too long for the head and the end of the plug was hanging out in the combustion chamber! The exposed threads on the end of the plug have carbon built up on them or chemical oxidation. Tough to crank that through the head. Be patient. little out, back in little out back in. Chances are you'll get it out without wrecking the head or snapping off the plug.
Pick a heat range.
Summary: If you have no idea where to start picking a heat range, error on the cold side to prevent engine damage. Replacing a fouled plug is easier than replacing a holed piston.
Hot or cold plug? Why do I care?
When selecting a heat range for a spark plug for your engine the way you are running it, the goal is to get a plug that runs hot enough to prevent fouling, but stays cool enough to prevent pre-ignition. This way you get long reliable service life for both plugs and engines.
You can't tune an engine with different plugs. Too rich will still run too rich with different plugs. You chose plugs to match the engine running conditions, so tune it up first before you start trying different heat range plugs.
What you are looking for is a grey plug center electrode. White = plug running too hot. A glowing hot plug tip can light off your mixture way too soon. Pre-ignition. This is really hard on your engine.
Black plug is too cold. It can't get hot enough to burn off deposits on the plug. Build up enough black stuff on the plug and it will rob or mask your spark and maybe even short out the gap between the electrode and the ground strap. That is a fouled plug.
Grey is just right. They used to say light brown/tan is right, but I think that is the color we used to get with methyl ethyl lead. I just don't see it anymore. *shrugs*
Why does one heat range plug run hot and another runs cold? It has to do with how much of the center insulator is in contact with the plug body. The more contact area, the more heat it can sink from the center electrode to the cylinder head and the colder the plug stays. Hence...a "cold" plug.
Different plug vendors use different hot-cold numbering systems. Champion and Autolite is like a thermometer. Higher numbers are hotter plugs. NGK is the opposite! The hottest NGK is a 2 and the coldest is a 12. Sneaky, eh?
Our low compression, low rpm, maybe a little more worn out oily engines might want a plug towards the hot side of normal to keep from fouling. Just check'em to make sure you are not white hot. That pre-ignition is mighty hard on ring lands.
There are many factors that affect plug temps. Mixture, RPM, compression ratio...lots of stuff. So many different variables that all come down to one thing. Getting a plug that is hot enough to not foul and cold enough to not cause pre-ignition in the conditions you are running it. So go on your test loop run, come back and pull a plug. Hopefully, you'll find you have the right plug for the job already in there.
Gap: Gotta 6 volt? bet your gap is about .025" Gotta high zoot 12volt ignition system? Bet you run a bigger gap like .030". I'll stick to the Studebaker book which runs from .025 to .028" depending on the book. Sure when you pull a plug and test for spark she'll throw a good 3/8" spark, but that won't happen under the compression inside the engine. You want as much gap as your coil will jump *reliably* in the engine to increase the chance of lighting off the charge.
Plug design/manufacturer:
Ha. You are on your own here. I'm sticking with a decidedly low tech, high quality, spark plug like the standard NGK or Autolite plugs for my Champion 6 flathead engine.
No need for long life platinum, or iridium on my Willys. The plugs are easy to change on the champ 6 anyway.
I don't feel the need for multiple ground straps, double or triple split ground straps or cut back ground straps.
I don't need ice cold race plugs in this low compression, low RPM engine. (NGK's race plugs have the SAME technology as the standard plugs, just colder heat range!)
I still run points and I don't have a radio so I don't even need resistance plugs to combat Radio Frequency interference.
How I picked plugs for my engine: The "book" calls for a long gone Champion J7. A 3/8 reach plug! The Military guys find short reach plugs for the "weasel" engine (same as my champ 6) in their field manuals too. But my Dad the Mustang racecar guy, my own experience, and almost every flathead post I can find says never pocket a spark plug. (plugs that don't reach the combustion chamber). OK. MAYBE the nitrous oxide guys and methanol racers want to control the flame front, but I dunno. As long as the valve doesn't hit the plug, we'll be OK. I have at least .125" before the valve hits with standard 3/4" reach plugs. Plus, a pocketed plug is a foul-a-matic because it never sees the high velocity hot escaping exhaust gasses that help burn off deposits on the plug. The plugs I pulled out were 7/16th reach extended nose made in USA Champion plugs. closer to the combustion chamber but not in it and not the "right" plug either. They were pretty well coated in black carbon. I'm going to go against internet wisdom (rhetoric?) here and go with plugs with a reach that matches the heads. So far, so good. runs pretty well.
NGK plug decoder chart link
www.sparkplugs.co.uk/pages/technical/NGK-spark-plug-code.htm
plug heat range chart for some vendors:
www.autolitesparkplugs.com/learning-center/article/225/heat-range-conversion-chart
Break it down:
Champ 6 has 14mm plug holes. That's a "B" on the NGK chart.
Champ 6 is a low performance engine, I'll start with a normal heat range. that's a "7" or "8" on the NGK scale.
Champ 6 stock head is a 3/4" reach head with a flat gasket surface. that's an "E" on the NGK chart.
Champ 6 is a stock engine without special needs. A standard electrode is just fine. That is an "S" on the NGK chart.
so I want an NGK, B7ES spark plug. Down to the car parts store in town and sure enough, they've got 'em on the shelf!
