Spark Plug Changes

[radman]

Cars that have a greater number of cylinders than the FJR will also fire their individual plugs far less often.

Any car or any engine (4 stroke) for that matter, no matter how many cylinders, 1, 2, 4, 6, 8, 10, 12, will fire their spark plugs once every other revolution.

A V12 Mercedes engine will fire it's plugs the same # of times as our FJR's will at 4,000 RPM's.

Which is why an increase in the number of cylinders in an engine generally means smoother power output.

 

[dcarver]

Rad will like this..

Back in my late teens I built a variable high voltage, variable air-gap, spark plug tester that was housed in a hermetically sealed chamber that I could change pressure and humidity in. I used it routinely to find which plugs fired best across the air/humidity/pressure gap the best -

..for my lawn mower . Hey, it was more an electronic experiment than anything else.. (and no Rad, I could not simulate combustion pressure, 200 psig was all I could do.. .. but my lawnmower always ran GREAT!

Kind of wish I still that monstrosity of test apparatrus.. it was ugly, malformed, but worked great. I later used the high voltage system for other purposes..

 

[charismaticmegafauna]

Cars that have a greater number of cylinders than the FJR will also fire their individual plugs far less often.

Any car or any engine (4 stroke) for that matter, no matter how many cylinders, 1, 2, 4, 6, 8, 10, 12, will fire their spark plugs once every other revolution.

A V12 Mercedes engine will fire it's plugs the same # of times as our FJR's will at 4,000 RPM's.

Some cars with electronic 'coil-pacs' fire multiple plugs -- just like the FJR. IOW, every revolution -- not all cars have distributors anymore.

Which is why an increase in the number of cylinders in an engine generally means smoother power output.

True, generally -- one must also consider rod throw phasing, angle of the bores (if a 'V' config), and maybe more -- given enough cylinders and the point is probably moot...... Angle of crank throws and their overlapping is directly related to smoothness -- in-line six (4-stroke) w/120 degree throws is, usually, the model of smoothness. In-line four -- not necessarily so (a heavy fly-wheel can help...).

 

[jestal]

Cars that have a greater number of cylinders than the FJR will also fire their individual plugs far less often.

Any car or any engine (4 stroke) for that matter, no matter how many cylinders, 1, 2, 4, 6, 8, 10, 12, will fire their spark plugs once every other revolution.

A V12 Mercedes engine will fire it's plugs the same # of times as our FJR's will at 4,000 RPM's.

Not necessarily true. It depends on the type of ignition system. A conventional ignition system on a four stroke engine (typified by a distributor) will indeed fire the plug every other revolution of the crank. However, direct fire systems (usually identified by multiple cylinders fired by a single coil) fire the plug EVERY revolution of the crank. In fact, the FJR is just this type of system that fires it's plugs every revolution, not just every other revolution. With only two coils to fire 4 cylinders each coil must fire two cylinders. One cylinder will be on the compression/power stroke and the other will be firing on the exhaust stroke.

The idea, that a four stroke engine actually needs the spark plug to fire every other revolution, is correct. The fact is that many many ignition systems on four stroke engines fire the spark plug every revolution. The plug arcs on the exhaust stroke as well as on the compression stroke. Waste spark it is called.

While is seems to make common sense that firing the plug every revolution would "wear it out" sooner than firing only on the compression/power stroke the fact of the matter is that there is precious little difference in wear on the plugs from the waste spark cycle.

Personally, I wouldn't consider changing the iridium plugs for 50k miles unless you notice some sort of misfire or other driveability issues. Short trips and many cold starts without sufficicent warmup to clean off the plugs would shorten the life of the plugs and only one serious fuel fouling situation could ruin the plugs at any mileaage but in normal use the iridiums should go on virtually forever.

 

[jestal]

Which is why an increase in the number of cylinders in an engine generally means smoother power output.

True, generally -- one must also consider rod throw phasing, angle of the bores (if a 'V' config), and maybe more -- given enough cylinders and the point is probably moot...... Angle of crank throws and their overlapping is directly related to smoothness -- in-line six (4-stroke) w/120 degree throws is, usually, the model of smoothness. In-line four -- not necessarily so (a heavy fly-wheel can help...).

There are two things that determine engine "smoothness" that are often confused: engine balance and firing frequency.

The type of engine, rather than the number of cylinders will determine how well the engine can be balanced mechanically....multiple cylinders do not necessarily help with this at all.

Firing frequency, or better stated, the even-ness of firing frequency, is also a large contributor to the sensation of engine smoothness. If the engine firing events come in regular intervals then the engine will feel smoother than in another situation where cylinders fire un-evenly.

An engine can be mechanically balanced and have un-even fire and it will NOT feel smooth.

An engine can have a lot of cylinders and have even fire and not be mechanically balanced and it will NOT feel smooth.

There is no simple answer to this situation.......LOL.

An example of this is a 90 degree V6 engine. With the addition of a balance shaft this engine can be mechanically very smooth. Without a split pin crank, however, the firing will NOT be evenly spaced so the engine will feel rough even though it is very close in terms of mechanical balance.

Having a lot of cylinders does help, certainly, with smoothness. There are V10's that are not mechanically balanced perfectly and do not have even fire but they still feel pretty smooth in relative terms.

 

[Fred W]

...and then there is the rotary engine, which has no cylinders, even firing and is incredibly smooth. I've owned 2 cars with twin rotor engines ('75 RX-3 and an '88 RX-7). The engines in those cars were a thing of beauty. So small, and yet so powerful and smooth.

To get back (closer to being) on topic, the rotary engines have two spark plugs per "cylinder" (rotor actually), arranged in the rotor casing such that one was more advanced than the other. As the rpm rose the second plug would begin firing and it felt like the turbo was kicking in, except neither of mine were turbocharged.

Everyone should experience a rotary engine at least once in their lives. If you ever have a chance take one out for a spin

I've yet to drive an RX-8, which is a good thing or I'd likely end up with one in the garage...

 

[Geezer]

...and then there is the rotary engine, which has no cylinders, even firing and is incredibly smooth. I've owned 2 cars with twin rotor engines ('75 RX-3 and an '88 RX-7). The engines in those cars were a thing of beauty. So small, and yet so powerful and smooth.
To get back (closer to being) on topic, the rotary engines have two spark plugs per "cylinder" (rotor actually), arranged in the rotor casing such that one was more advanced than the other. As the rpm rose the second plug would begin firing and it felt like the turbo was kicking in, except neither of mine were turbocharged.

Everyone should experience a rotary engine at least once in their lives. If you ever have a chance take one out for a spin

I've yet to drive an RX-8, which is a good thing or I'd likely end up with one in the garage...

And I owned a '76 RE5 Suzuki single rotor motorcycle and it vibrated like a cement mixer under power. I never understood why that engine didn't run smoother. It had a single special purpose spark plug.

 

[Fred W]

...and then there is the rotary engine, which has no cylinders, even firing and is incredibly smooth. I've owned 2 cars with twin rotor engines ('75 RX-3 and an '88 RX-7). The engines in those cars were a thing of beauty. So small, and yet so powerful and smooth.
To get back (closer to being) on topic, the rotary engines have two spark plugs per "cylinder" (rotor actually), arranged in the rotor casing such that one was more advanced than the other. As the rpm rose the second plug would begin firing and it felt like the turbo was kicking in, except neither of mine were turbocharged.

Everyone should experience a rotary engine at least once in their lives. If you ever have a chance take one out for a spin

I've yet to drive an RX-8, which is a good thing or I'd likely end up with one in the garage...

And I owned a '76 RE5 Suzuki single rotor motorcycle and it vibrated like a cement mixer under power. I never understood why that engine didn't run smoother. It had a single special purpose spark plug.

Yeah, I had heard those didn't work out as well as the Mazda twin rotors. Maybe you need the two rotors aligned 60 degrees out of phase with each other to cancel each other out? There were even a bunch of 3 rotor engines out for a while. I guess they must have offset the rotors by 40 degrees on those? With a tubocharger they made silly amounts of horsepower.

 

[mike25]

To get back (closer to being) on topic, the rotary engines have two spark plugs per "cylinder" (rotor actually), arranged in the rotor casing such that one was more advanced than the other. As the rpm rose the second plug would begin firing and it felt like the turbo was kicking in, except neither of mine were turbocharged.

The second plug (trailing plug) fires all the time, along with the first (leading plug). What your feeling

on your 88 RX is the six port system coming on at higher rpm's. Ya, rotory's are cool, iv'e raced them

for years.

 

[Fred W]

To get back (closer to being) on topic, the rotary engines have two spark plugs per "cylinder" (rotor actually), arranged in the rotor casing such that one was more advanced than the other. As the rpm rose the second plug would begin firing and it felt like the turbo was kicking in, except neither of mine were turbocharged.

The second plug (trailing plug) fires all the time, along with the first (leading plug). What your feeling

on your 88 RX is the six port system coming on at higher rpm's. Ya, rotory's are cool, iv'e raced them

for years.

Now that you mention it, I remember that now too. There was some kind of maintenance I had to do to allow the port actuator to open up the extra ports. It used to get gummed up occasionally. The RX-3 was kind of cool coupe. Where the '88 had FI the '75 had a little 4 barrel carb on it. But I sold the RX-7 many years ago now and haven't had the pleasure of a rotary since.

 

[mike25]

Ya, I also think the RX3's are cool.

It's also for sale.

 

[Fred W]

Ya, I also think the RX3's are cool.
It's also for sale.

Mine didn't look anything like that. That one looks awesome...

 

[painman]

Ok, no pat answer's here and not sure if I should start another thread, but on plugs intervals involving iridiums vs. stock, and Warchild says if you stay with the stock plugs stay with the 8 thousand mile change intervals, and I am at the 8 thousand mile mark and the factory says 8 thousand miles plugs changed. Now I want to change out the stock plugs and install iridiums so I don't have to change them every 8 thousand miles, but my question is I've heard of some other's who had brought their bike into the dealer for warranty work and were hasseled for having a non-stock oil filter on their bike even though the warranty work did not envolve oil or engine failure due to lubrucation issues. So if something would occur that I brought my bike into the dealer for warrantee work, and said dealer says, oh, these are not stock plugs and they weren't changed at 8 thousand miles according to your maintaince record......what does one do? I know this question could be shot down by those here in many ways but think it is a valid one. Not only for me but for others especially new bike owners for future reference. And I really don't want to keep stock plugs if they aren't of quality. Any help? PM. <><

 

[odot]

Me thinks you can't get into trouble for having aftermarket oil/plug stuff on....otherwise the company would have to supply you with new items free of charge.

 

[jestal]

Soo....for all the Wankel buffs....is it true that most everyone runs a small amount of two stroke oil in their gasoline (premix) to keep the rotor apex seals alive....???

 

[Fred W]

Soo....for all the Wankel buffs....is it true that most everyone runs a small amount of two stroke oil in their gasoline (premix) to keep the rotor apex seals alive....???

No. Maybe the racers do, but not the street cars. The engine pumps crankcase oil into combustion. You "use " your regular oil and just have to keep an eye on the level.

 

[Toecutter]

So if something would occur that I brought my bike into the dealer for warrantee work, and said dealer says, oh, these are not stock plugs and they weren't changed at 8 thousand miles according to your maintaince record......what does one do?

What's a maintenance record?

 

[mike25]

Soo....for all the Wankel buffs....is it true that most everyone runs a small amount of two stroke oil in their gasoline (premix) to keep the rotor apex seals alive....???

No. Maybe the racers do, but not the street cars. The engine pumps crankcase oil into combustion. You "use " your regular oil and just have to keep an eye on the level.

I run 1 oz. of Redline (sponsor) 2 stroke oil per gallon of fuel in the race car, the stock oil injector pump is removed,

and plugged. Also running ceramic apex seals, which are nearly indestructible. The stock system is fine for the

street, but if doing a track day (i also have a twin turbo) a few oz,s of oil helps.