Topic: Sparkplugs, naked

[HondaMan]

I cut open the working areas of some of our sparkplugs so everyone can see them.
Here's the collection.

[HondaMan]

Here's the more commonly-used, non-resistor types.
The dimensions noted are in inches.

[HondaMan]

Here's the resistor-type versions. In ND's plugs (which includes the NGK brand) the resistors are used to heat the tips, sort of a 'fast warmup' sort of design. In contrast, Champion plugs used to have the resistors up in the ceramic heads of the plugs, which sometimes led to the characteristic loss of the seal between the ceramic and steel partss of their plugs. The ND design heats up emission-controlled engines faster, for less smog.

[HondaMan]

When you hear terms like "this plug has a [longer/shorter] tip for [hotter/colder] operation, this difference is measured in thousandths of an inch, typically 0.008" or so between heat ranges 7-8-9, and 0.015" in heatranges 5-6 (in NGK-reference).

"Hotter" tips may also have thinner ceramic at the end of the tip, which conducts less heat back to the engine. This thickness difference is likewise measured as a few thousandths of an inch.

The ND designs locate the resistor inside the combustion chamber where the engine heat can help compress the metal contacts against the resistive element, which may be ceramic or carbon (most are a mix of both in the ND designs). Typically when the plugs are cold this contact may be open, if read with an ohmmeter, because it will grow considerably with heat. Thus, measuring resistor plugs on the bench can be problematic unless the plug is hot or brand new and hasn't yet been heat-cycled hard enough to seat the metal contacts against the resitive chunk in the tip. Thus, the ND version will heat up the plug tip faster and help ensure the contact is made, once the engine starts. The pressures are in the hundreds of pounds range on the resistive element. This is what eventually wears them out over time.

If you have seen older pictures (mostly Champion or AC Delco) of sparkplug heat ranges, you probably noticed long, thin tips on "hotter" plugs and shorter, thicker tips on "colder" ones. this is where the old terms of "extended tip" or "protected tip" came from: automotive sparkplugs (water-cooled engine temperatures are much lower than our bikes' engines) often have very thin tips to help burn off deposits at the center electrode by NOT removing the heat from those tips. And, in the old V8 wedge-engine designs of Detroit engines, these tips could stick way out of the plugs without hitting anything in the engine, as there was plaenty of space in a 400+ cubic inch engine's chamber. Heck, a Ford 390 chamber, closed, is bigger than all 4 of my 750's chambers added together, at 102cc !

[BenelliSEI]

Fascinating reading and info..... Thanks!

What did you use to cut open those plugs so carefully?

[HondaMan]

Fascinating reading and info..... Thanks!

What did you use to cut open those plugs so carefully?

Well...my right thumb is still bleeding today, but...I used 3 sizes of cutoff wheels in a Dremel hand tool. Large one to start the cuts, smaller one to get into the corners, and a real small one to thin the thread jacket down far enough to break them off and grind away the flash. That stuff is SHARP in the end! I'm surprised I didn't bleed on the paper!?

[BenelliSEI]

3 X thanks! I managed to print the two pictures and your notes. Really good info, permanently in my binder of “Stuff I Should Know, But will NEVER Remember”.

[Deltarider]

Thanks Hondaman for sharing pics of what must have been quite a job. We now can make visual comparisons.
The following might be interesting for CB500/550 riders, especially in Europe. Originally the CB500 model came with the D7ES plug. Before I began maintaining my CB500 myself, I had it serviced at least two times by an official Honda dealer. They have always fitted the D8ES-L sparkplug. According to p.83 of a French manual*, which was composed in close cooperation with Honda France, with the arrival of the K1 there the CB500s had the D8ES-L fitted. In Holland, after the break-in period, dealers also would fit the NGK D8ES-L sparkplug. When I asked why this was - the CB500 owner's manual specifies the D7ES type - the answer was that the D8ES-L was a better choice, seen the cruising speeds these bikes were operated at on the highway. I don't rule out that this preference for the D8ES-L had even been a directive by the importer, Honda Nederland.
About these cruising speeds, in my archives I have several riders reports and in all of them owners reported an average cruising speed of 130km (80 miles). On a CB500 that equals a 6500 RPM in top gear. Maybe importer and dealers, knowing this, wanted to be on the safe side, but there's more. Forsaid French CB500 Manual on p. 83 points at the particularité of the D8ES-L being autonettoyant which means selfcleaning and recommends them for the earlier CB500s all the same.
That last recommendation is my starting point for a bit of guesswork. The CB500 was launched in 1971. Now these bikes had been assembled some time before ofcourse and likewise had the Owner's Manuals been written long before the bikes were in the showrooms. Could it be that when the first CB500s were being assembled and the owner's manuals composed, the NGK D8ES-L sparkplug was not around yet?
Realise that in general these bikes in Europe have indeed been used differently than those in the US. This has to do with a difference in infrastructure. In the US it is quite common that when you leave home, you walk to a vehicle, even to buy a loaf of bread. It's an automatism. In Europe and certainly Holland the situation is different. Shops are nearby and to do your shopping, you just walk or ride your bicycle. Cars and motorcycles are reserved for longer distances. So in the US in general these bikes will see more shorter rides than ours do. BTW, the in this forum often called out 'poor' charging system which never has been reported as such in Europe, also indicates to that. This difference in usage could well explain the preference in Europe for the D8ES-L, also for the CB500/550, where the US sticked to the D7ES. Anyway, with this in mind, any of you can decide for him self what plug is best for his rides. If your CB500/550 sees over 5000 rpm often enough, you may consider the D8ES-L which for me has always been a superb plug.
* From that same French manual I learned that NGK had the letter 'S' for plugs that were thermo-elastique and multithermique.

[HondaMan]

You're right on the money about the D8ES-L plug, Delta. They were created by ND at Honda's request in 1970 for the plug-fouling problems in the CB750K1 bikes, and became standard parts for the 750 after that. I ran them in my own CB500 (1972) because I, too, lived where it was miles and miles to the nearest [anything], so it got a high-speed workout every ride. The original version of the plug was the ND X22ES body (slightly colder than a D7ES), but with a thicker and longer center ceramic, not quite as much as the D8ES. Later the tip was modified to stick out another 0.008" into the chamber, which gave it a characteristic look and cleaner tip, becoming the "-L" type. ND then brought out their so-called "Hot U" series plugs in 1972, which, in the X24ES-U series, was a thinner ceramic tip than the NGK versions so there was more flow around the ceramic. This also burns off some carbon, and became my favorite ever since as it matches my riding style (4000 RPM minimum, always) on my 750. The 500/550 runs similar RPM, naturally, so they like this plug, too. I still prefer the X22ES-U in the CB550 today (in the States) because the ethanol that is added to our gasolines burns much cooler, and plug fouling can be a problem again with the CB550/500 engines in city riding here.

Somewhere in my old boxes of stuff I have 2 plugs D7ES-L. I got them from a 2-stroke bike out of California (Suzy GT550) that came thru one summer day, touring, and he had a cracked plug with a bad miss on the center cylinder. These 2 of the 3 in that bike are the only ones like it I have ever seen, though. Their tip sticks out a little more than the D8ES-L plugs. I don't think they were around long: that was in 1973! So, there were lots of odd things for a while in the 1970s when touring took off like it did.

[bryanj]

A lot of years ago I was recommended to fit D7EV plugs to my 500 by our NGK rep who happened to be a well renowned sidecar racer, they worked really well, stated quicker, ran better and gave more MPG. good luck finding any now as they are long obsoleted

[HondaMan]

Somehow that whole -EV series disappeared(?).
The closest thing we have now to the old D8ES-L is the modern X24ES-U, and the modern X22ES-U for commuting service works in both the 750 and the 500/550 nicely.

The DRP8EA9, harder to find, works fine with the OEM coils while also improving the spark duration with the low-ohm coils like 3.0 ohm Dyna or ACCELs. It has a long, extended tip that rises above the fast-moving surface swirl in the 750 head, but it still allows use of low-octane (regular) even on the hiway.

[bryanj]

I think the EV range dissapeared as it cost more for 1 plug than 4 standards so only idiots like me who listened to knowlegable older people and racers bought them mate.
They do turn up occasionaly and i do have a couple of sets of the D7EV hidden in my stock for my use