Topic: Spark Plug Caps - NGK

[RSchaefer]

OK did a bunch of searching but did not find the answer.  For reference I have a '75, CB750F.

I am looking to replace my plug caps with the 5K resistor NGK's and don't know if its suppose to be the 102 degree or the 120 degree for cylinders 1 & 4.  Also I'm not sure on the right "size" of cap.  Its looking like on the NGK cap reference pages that the 102 degree or their "X" series has a reach of 70mm, which is comparable to their straight cap or their "S" series (cylinders 2 & 3) with a reach of 77mm.  The 120 degree cap or their "V" series, which is what they call their "Long" version of their 120 degree cap has a reach of 42.5mm.

So which is it, seems it should be the 102 degree or their "X" series?

Also they have the 10mm/12mm caps ("D" option) and the 14mm ("B" option) - So I am electing to install their Iridium DR8EIX plugs, which measures 10mm at the insulator so I assume I need the "D" option?

In looking at the Z1 site they have ALL of these options so its not like going to the Z1 site provides an answer?

ALSO NGK offers an "E" option (terminal nut, 6.6mm opening) or an "F" option (terminal stud, 4.1mm opening) for the plug terminal.  The Iridium DR8EIX plugs I got did not come with a "nut" installed on the top of the plug, just has the stud, so I assume I need the "F" option?

OK and last but not least they offer a "P" option (with special water-proof cover)!

Thus the reason for all of my confusion, all of these options.  Based on my measurements it would appear I need 2 - SD05FP's for cylinders 2 & 3 and 2 - XD05FP's for cylinders 1 & 4.

Does this make sense?

Has anyone tried the "P" option that NGK offers i.e. "with silicon water-proof cover?"

[nccb]

good lord, that is confusing for us small brains

[RSchaefer]

I agree I thought it was a simple matter of ordering caps for my CB750???

[scottly]

The 5K ohm NGK caps I got a couple of months ago were part numbers VB05F and SD05F.

[CoachDoc]

I seem to recall the NGK website has a selector to choose the proper fitment for plug caps. I used it and they got me the right stuff. I believe Scott has it right.

[bollingball]

The 5K ohm NGK caps I got a couple of months ago were part numbers VB05F and SD05F.

Exactly the same for me on my 78 750K from Z1
Ken

[Chachi]

This may not help b/c it is specific to the 500... but passing the link on anyway...

http://forums.sohc4.net/index.php?topic=105814.0

[bjbuchanan]

The stud nut type is for the solid larger one, description says 6.6 mom vs 4 something for the the stud one. The stud one is the threaded type of plug that came stock, you can always screw on the larger but style piece to it.

[RSchaefer]

Well I went with the SD05FP's for cylinders 2 & 3 and the VD05FP's for cylinders 1 & 4.  The V for 1&4 is 120 degree and a 42.5mm reach, which appears to be the same as the stock caps.  The D in the part number means they would fit over 10 to 12mm spark plugs versus the B which is 14mm.  Not sure why you would be mixing B's and D's on the same bike unless you were using different plugs in 1&4 verses 2&3, makes no sense.  The P at the end of the part number is for the waterproof silicon caps at either end of the hard plastic cap.

[bjbuchanan]

I know you already placed your order but I am just trying to clear my terrible autocorrected post. I use my phone usually and don't always check over the post

The "stud" type is the threaded end type plug and that is why it has the smaller opening for the plug, also has a slightly different "attachment" in the cap. The nut is the solid bulbous style one that most modern plugs have. You can usually just screw on these little adapter things that come with some older outdated plugs that make it just like nut type for the stud type plug.

[RSchaefer]

Yes I got that, that the 4.1mm opening verses the 6.6mm opening, stud versus nut.

For something as simple as a plug cap, man there are allot of options.  My problem was in going to the Z1 site and seeing many many options.  Obviously they do Kawasaki's as well and I suppose there are different spark plug widths at the ceramic for the CB750.  I went with the Iridium DR8EIX and they are 10mm at the ceramic verses 12 or 14mm which further confused me as it seemed that some were ordering the 10/12mm for cylinders 1&4 and the 14mm plug caps for 2&3?

Anyway I just sat down and figured it out myself, I thought with everyone else here that someone else might have found themselves in this quandary.

[scottly]

I went with the Iridium DR8EIX and they are 10mm at the ceramic verses 12 or 14mm which further confused me as it seemed that some were ordering the 10/12mm for cylinders 1&4 and the 14mm plug caps for 2&3?

Why did you go with resistor spark plugs along with the 5 K ohm caps??
As far as the ceramic size, I never measured it, but the cap part numbers I posted fit the stock NGK plugs just like the original caps, including the rubber seals. I went to the local Honda shop armed with a multitude of options from the NGK site, as well as two of my old caps; the counter guy was an old fart like us, and immediately knew what caps I needed.  

[RSchaefer]

Did not even give that a thought, I got the Iridium from DynomanPerformance.com as the replacement for the stock CB750 (DR8EIX, NGK #D8EA and #DR8ES equivalent, Sold in box of (4)).

What would the effect being of combining the DR8EIX and the 5K caps?

[chickenman_26]

You're fine. There won't be any degrading of performance. The resistor caps and plugs are mostly about eliminating radio frequency interference. In years past, the RFI introduced horrible static into the AM radio of a car sitting next to you at a stop light. These days, it's more about keeping RFI from messing with the ECM. Most modern vehicles use both resistive wires (or caps) as well as resistor plugs. I've been using resistor Iridium plugs in my bikes for years when a non-resistor version isn't available, along with the 5k ohm caps, and they all run well.

FYI, the reference to 10, 12, or 14mm plugs is about the thread diameter, not the diameter of the porcelain. The 14mm plugs have a larger diameter porcelain than the other two. So if you used a B prefix cap on a 10 or 12mm spark plug, the connection would be exposed to water and dirt.

Stu

[RSchaefer]

Good to know Stu!  So the '75, CB750 is 10mm or 12mm spark plug?

In looking at the NGK spec page I see where this option is for the "Plug Thread Size" funny others who have responded here used the 10/12mm thread size in say 2&3 while using the 14mm in 1&4.  I assumed that would mean a less secure grip of the silicon sealing cap at the end of the actual plug cap.  I suppose if you used the original rubber sealing caps instead of getting the ones from NGK i.e. the "P"option at the end of the part number you would be OK.  That said I could see where the inside diameter of the plug cap must be larger on the 14mm option due to an increase in the diameter of the ceramic.  Boy am I anal!

I was reading that the original caps for the CB750 were 7.5K or 10K but that these are unattainable but more desirable than the 5K.  That apparently the increased resistance would increase the, lets say current of the spark at the end of the plug, OK lets say voltage, in any case more punch in the combustion chamber and thus better combustion.

I see where some guys are even going to resistive coil wire and the 5K caps in order to increase this resistance.  I suppose most of this ends up being an advantage akin to the size of mice nuts in the grand scheme of things!!

[chickenman_26]

Good to know Stu!  So the '75, CB750 is 10mm or 12mm spark plug?

12mm

Stu

[chiefw]

Just a quick follow up in case anyone stumbles across this thread:

The NGK PDF that explains the codes: https://www.ngkpartfinder.co.uk/files/NGK_Spark_Plug_Covers.pdf

I prefer the VD05FP and SD05FP for my CB750k. But VD05F and SD05F will work as well.