Topic: Where to get spark plug caps?

[B.O.X.N.I.F.E.]

Is there not a DR7ES-L plug?

No, there is (still?) a DR8ES-L plug. but I don't know if there is any difference with the DR8EA plug.
It seems DR7ES is superseded by DR7EA. Again, I don't know if there's any difference.

I agree with Hondaman: Denso is the better plug. Guess what brand is hard to find here. NGK you can buy everywhere and that's the way it is.

For everyday street use wouldn't you want a DR7, not 8?

[Deltarider]

No, most 500/550 riders in Europe used 7 only during break-in period. But then, we tend to ride our bikes a bit livelier. Contrary to USmarket (maybe), all inline 4 GS's (Suzuki's) and Z's (Kawasaki's) I know, had "8"'s.

About the 400: doesn't it have electronic ignition?

No, it has the same points ignition as the other Four's.

[andy8190]

haha i started a good thread

[TwoTired]

The Honda dealer always tried selling me D8 plugs for 550's (thinking they used the same plugs as 750s).  I actually took them home one time and put them in the bike just to see what they did.

They made the engine VERY cold blooded, to the point where you couldn't ride it until it had warmed up at least 5 minutes.  After warm up, it was fine.  However, the Butt dyno couldn't tell any difference in running or acceleration while squirting through traffic or on the hiway.  They were pure hell in the winter where you needed a 15 warm up before any riding could be done expecting a reliable throttle.

If you want a mild mannered 550, use the D7EA.  With these you can suit up, jump on, and drive off with some choke on.  Then gradually reach down and incrementally take some choke off while the engine warms.  After a few blocks, the choke is off, and the idle is reliable.

With the D8s the engine is a bucking unpredictable beast until it warms up.  The Honda manual recommends the D7 plug for a reason.  And, my experience is that their recommendation is sound, certainly for all the US models without the odd carburetors and inlet restrictors, anyway.

Cheers,

[HondaMan]

Is there not a DR7ES-L plug?

No, there is (still?) a DR8ES-L plug. but I don't know if there is any difference with the DR8EA plug.
It seems DR7ES is superseded by DR7EA. Again, I don't know if there's any difference.

I agree with Hondaman: Denso is the better plug. Guess what brand is hard to find here. NGK you can buy everywhere and that's the way it is.

Can you find the Bosch equivalent? They are also quite good, but can't be had here in the U.S. Their D8E crossover plug is like a D7.5 heatrange.

The DR8ES-L plug has the extended tip. If you hold the two side-by-side, you can see it: if you also take a thin wire and gage the depth of the center electrode into the body, you will find it longer on the -L, but not as long as a D7. In terms of heat range, the -L is sort of like a D7.5 plug: in one test during the summer of 1973 I found the oil temps to be lowest with the D8 and D9 plugs (D9 disappeared in 1974), highest with the D7 plugs, and between with the D8ES-L plugs. Interestingly, the X24ES-U plugs yielded less oil heat than even the D9 plugs, yet they stay cleaner. That's one reason why I've run them almost exclusively since 1974. 

[B.O.X.N.I.F.E.]

Is there not a DR7ES-L plug?

No, there is (still?) a DR8ES-L plug. but I don't know if there is any difference with the DR8EA plug.
It seems DR7ES is superseded by DR7EA. Again, I don't know if there's any difference.

I agree with Hondaman: Denso is the better plug. Guess what brand is hard to find here. NGK you can buy everywhere and that's the way it is.

Can you find the Bosch equivalent? They are also quite good, but can't be had here in the U.S. Their D8E crossover plug is like a D7.5 heatrange.

The DR8ES-L plug has the extended tip. If you hold the two side-by-side, you can see it: if you also take a thin wire and gage the depth of the center electrode into the body, you will find it longer on the -L, but not as long as a D7. In terms of heat range, the -L is sort of like a D7.5 plug: in one test during the summer of 1973 I found the oil temps to be lowest with the D8 and D9 plugs (D9 disappeared in 1974), highest with the D7 plugs, and between with the D8ES-L plugs. Interestingly, the X24ES-U plugs yielded less oil heat than even the D9 plugs, yet they stay cleaner. That's one reason why I've run them almost exclusively since 1974. 

You run the X24 in a 750 though, right? I thought the rule of thumb was D8 for touring/trips, D7's for everyday use in the 550.

What would be a 5k resistance plug in the #7 heat range? If you're running the aftermarket 5k plug caps it sounds like this would be what you'd want for everyday use on a 550.

[HondaMan]

Well, like TT's notes above show, the DC resistance is a lot lower than thousands of ohms. Don't confuse turns ratios with ohms?

I was referring to the secondary resistance, as TT noted:

This is straight DC resistance, not impedance.
14.50 KΩ
14.92 KΩ
14.89 KΩ

Let's just call it an average of 15k ohms.

There were 6 plug caps on these sets.  Since I had everything on the bench I measured those, too.

11.02 KΩ
11.29 KΩ
9.56 KΩ
11.2 KΩ

Call it an average of 11k ohms.

Since you have two resistors per coil (one per plug) the total cap resistance would be 11k * 2 = 22k ohms. It's a bit higher than the secondary resistance, however the inductive impedence would be higher...

Leaning on my amateur radio days, I can't help to think of impedance matching antennas; you want the same impedance at the antenna and through the coax as you have at the transmitter. In other words, the transmitter's output impedance is 50 ohms. The coax cable has to have an impedance of 50 ohms, and the antenna should have an impedance of 50 ohms (as close as you can get it, freq dependent). This maximizes the power output of the system.

I wonder if the same idea could/should be applied to ignition coils...

Oh, I see what you're thinkin', and you're right on...I'm a First-Class RT Licensee, myself!

In the design of the coils, they are an autotransformer. So, the resistances are actually in parallel, since the "top" of the coil is a magnetic tie to the "bottom" of the primary, which is mechanically linked to the frame of the bike through a small paintless spot on the forward end of the coil mounts, on the front mount of the assembly. So, during discharge, this "magnetic ground" spot can be thought of as the "positive" terminal, at least for the first excursion of the AC waveform that becomes the spark's plasma bridge. For that moment, the resistors involved are both in parallel from the tip of the plug's electrodes , back to this 'ground' point, even though it is not a direct electrical circuit (it's coupled by magnetic field, instead). In effect, there is no "positive terminal" for the top end of an autotransformer, where you can touch it with an ohmmeter: you can only measure, in this case, from end-to-end of the loaded leads. The physical resistance, then, in each lead is one-half the total, or in this case, about (15k/2)=7.5K ohms. I'm sure that's where Honda's engineers first selected their values, for the 50% power transfer theorem to balance.

[Pinhead]

As I understand it, when the arc occurs at A and B, the secondary circuit is closed, and current flows through the secondary.  I would expect polarity to be consistent but opposite at each point A & B.

...the current flows from the B lead, across the B arc to "ground" (which really has no relevance here, as the head is simply a conductive path), Back up across the A plug arc to the A lead.

So that would mean the plugs and resistors are in series. But HondaMan is saying they're electrically parallel... I wonder how this could be measured.

[HondaMan]

The only way I know of with conventional instruments is to use a peak-reading voltmeter, in current mode, and measure the current in the high-voltage side from just one spark (or, if your meter is like mine, is takes 5 sparks to reach the 93% value, because it is charging a capacitor in a sample-and-hold circuit). Then, if you also measured the voltage, you could infer the resistance.

Your circuit, as drawn, is correct: the "top end" of the spark coils, where they are tied together, is the "other end" of the circuit, and the point most folks might label the (+) terminal. In an autotransformer, this spot is seldom available to a meter measurement, and it's an instantaneous reading, anyway, usually requiring an oscilloscope to read it.

When you know the turns ratio, though, you can infer the voltage: the spike that appears at the coil's (+)12 volts feed point magnetically echos the spark voltage in the autotransformer's junction of the two spark coils. In the Honda coils, this measures about 340 volts (see my old post during the development of the Ignition: it shows the scope traces I captured then). Using the turns ratio of 40 (that's what I rounded to during the design phase), the voltage at the "top" of the autotransformer is:

(340v * 40) = 13600 volts (in round numbers).

The autotransformer circuit then splits this voltage between the two coils, or about:
(13600 / 2) = 6800 volts per coil.

This is the typical voltage peak you see if you use a non-resistor cap and plug. If you add some resistance, the inductance will pump the voltage higher until the current can flow across the plug's gap. I don't know at the moment what the inductance of a 750 coil is (I have it somewhere, though), but this is where the stored "kickback" power in the condensor comes in handy: it allows a momentarily higher discharge current in the primary side to actually flow BELOW ground level (0 volts) to a value like -8 volts or so: this gives the secondary more electrical 'leverage' to build the spark voltage up a little higher (8 * 40 = 320 volts) to help ionize the spark plug gap. The capacitance value of the condensor becomes important for tuning this extra punch: typical is .024uF. When they get old and lose value, the spark voltage drops accordingly.

So, in the end, the spark voltage you see is this (6800 + 340) = 7140 volts, which is just enough to jump the 7mm gap (1000 volts per mm) in the Honda testers of old.

Convoluted, isn't it? 

[Pinhead]

If I understand you correctly, the plugs being in parallel, the current and thus polarity will be the same (and in phase with each other) at the "top" of each plug, which would be a "negative" voltage with regards to ground due to the collapsing field effect?

To make sure I understand correctly, if you were to place a high PIV value diode between points "A" and "B" would it have no effect due to the voltage being the same at those points (all else being equal)? Or would it short the spark out if the diode is "pointing" the wrong direction?

[HondaMan]

If I understand you correctly, the plugs being in parallel, the current and thus polarity will be the same (and in phase with each other) at the "top" of each plug, which would be a "negative" voltage with regards to ground due to the collapsing field effect?

To make sure I understand correctly, if you were to place a high PIV value diode between points "A" and "B" would it have no effect due to the voltage being the same at those points (all else being equal)? Or would it short the spark out if the diode is "pointing" the wrong direction?

That's right. They stay in phase through the whole collapse. It is an AC circuit, though: it starts with a positive excursion, then swings negative, then positive again, with the final physical jump typically taking place on the 2nd negative excursion, after which the current abruptly drops and the ionization of the gap falls away. The frequency is around  1400 Hz. For proof, look closely at the electrodes on both plugs of a given coil after many miles: you will see identical erosion patterns in the form of a spooning of the ground electrode: this indicates the ground arm is primarily negative during the larger voltage jump, as it supplies the electrons that migrate to the center conductor (remember electron flow is opposite that taught for "current flow"). The loss of electrons slowly becomes the loss of the atoms that make up the metal of the ground strap.

The "pulse" of energy at the top of the autotransformer must work it's way through the coil impedance and the spark circuit's resistance. As the first pulse appears at the 'top' of the transformer, the other end of the transformer correspondingly changes voltage (180 degree phase reversal). So, during this initial discharge phase, the two 'lower' ends of the transformer are pulling current from each other, and this discharges the engine cases. (Except, remember, that's at the same time that the OTHER coil is busy pumping current INTO the engine cases, referenced to the same magnetic ground on the frame at the coils' forward mount, but I really don't want to add that to this system discussion, just yet...  ). Now, the magnetic collapse generates say, "X" watts of energy (it's not like a battery, more like a ballon, or electrically speaking, a capacitor), and this energy can be considered to be at the top of the autotransformer as it heads for the coils. It has 2 paths to go, so the energy splits (hopefully in half) until this pulse dissipates, thus giving each coil X/2 of the wattage. So, when you go to add up impedances, using the rule of analysis of a series circuit and a battery at the "top", is a shorthand way of studying the resistances involved. In the end analysis, because of the limited energy available in the pulse itself, this analysis works, and is popularly used when the actual amount of energy is not known (like here, since we don't have the coil capacitance or inductance, just turns ratios and rough wire resistances).

Sorry, it's getting late, and I'm getting too technical...