Best Sparkplugs for 1967 230SL M127 motor

[67230SL-Vinny]

I've had Bosch WR7DC spark-plugs installed in my 67 230SL for the past 10 years, but just changed to Mercedes W7DC.
The car starts well and runs strong under power as it did previously, but with the recent change to the MB W7DC plugs, idle seems a tad rougher. Is there a difference in resistance or something?

I have Pertronix electronic ignition installed, and no adjustments were made other than installing the fresh MB plugs.
Unfortunately, the Bosch plugs got tossed.

Any thoughts or suggestions?

[rwmastel]

I've had Bosch WR7DC spark-plugs installed in my 67 230SL for the past 10 years, but just changed to Mercedes W7DC.
The car starts well and runs strong under power as it did previously, but with the recent change to the MB W7DC plugs, idle seems a tad rougher. Is there a difference in resistance or something?

WR7DC
W7DC

The R stands for Resistance.  Google can probably tell you how many Ohms.  You went from that to no Resistance.

[67230SL-Vinny]

Thanks Rodd,
As I learn more, apparently the original MB Plug wires had resistance built into the end tip of the wires. But replacement wires may not have this resistance, thus perhaps requiring the replacement plugs to have 'R'esistance built in.

I'll have to look closer at my plug wires, but I wonder if the resistance is just to suppress radio noise, or if it makes a difference in how they spark the ignition??  Especially as it may effect idle??

Everything was professionally tuned when they (Bud's) installed the PerTronix, they installed the Bosch WR7DC plugs.

[Benz Dr.]

Most resistor plugs run somewhere in the 4 - 5K ohm range. I used to use Bosch W9DC but they became unavailable so I switched to NGK BP5ES until that source dried up. In either case, both plugs are hotter than W7DC.

Most ignition wire sets are 1K ohms at the spark plug ends which is what you want. The small 90 degree ends are 1K ohms so you can add up a lot of unneeded resistance just through ignition wires. Look for a carbon core coil wire which is very common on Bosch wire sets - change to metal core wire and reuse the wire ends. Keep in mind that the ignition rotor is 5K ohms so adding resistance to this system will affect performance.

[rwmastel]

As I learn more, apparently the original MB Plug wires had resistance built into the end tip of the wires. But replacement wires may not have this resistance, thus perhaps requiring the replacement plugs to have 'R'esistance built in.

There's quite a lot to learn, but if you're into DIY maintenance and repair then this Group will be fun for you.  Here's a great place to start:
https://www.sl113.org/wiki/TuneupOverview/Start

There are links in there for related info, and overall it is a lot of reading.  But, knowledge is power!!  Educate yourself and you can do a lot of work on your car to save money.  Also, education allows you to talk more intelligently with mechanics at Bud's or elsewhere to keep from getting taken advantage of.

[67230SL-Vinny]

Great info Doc,
Do these plugs come pre-gapped correctly, or do gaps need to be set to M127 spec??

Thanks Also to Rodd,
The link you provided is awesome. Many of my questions answered, and much more to read and study.

Although I'm very mechanical I no longer do much wrenching on my cars. I agree knowledge is power. I try to diagnose my automotive issues , fix what I can, and otherwise try to help my mechanics zero in on what exactly needs fixing.

I purchased (3) I-Carsoft Mercedes OBD-II diagnostic tools I carry in each of my 'modern' W211 cars. Things like the dreaded 'Check Engine Light', resetting functions, or checking things like cam timing no longer scare me. No OBD-II port on the W113 though.     But I'm really more comfortable with the mechanical systems in our W113's.

[rwmastel]

Your Volvo must be a blast to work on!  I'll bet it's super basic.

[67230SL-Vinny]

The 57 Volvo Duett is a blast. So basic and everything so accessible. Parts are plentiful at reasonable prices as many of the drive-line components were shared with the 444, the 544, and even later 120 series Amazons stretching across 2+ decades. It was just featured in the Jan-Feb 2024 issue of Volvo Club of America's Rolling Magazine.
Even Santa can change the spark-plugs on this one. 

[Benz Dr.]

I set them to .032 which is the setting on new plugs.

[67230SL-Vinny]

Thanks Doc,
Same .032 gap as on new plugs makes it fool-proof.

[rwmastel]

The 57 Volvo Duett is a blast. So basic and everything so accessible.

Nice!  Yeah, very different from my wife's 2022 XC60 B6.  I can't imagine doing DIY diags and repairs on it's 2.0 4-cyl turbo w/ electric supercharger. 

[mdsalemi]

As I learn more, apparently the original MB Plug wires had resistance built into the end tip of the wires. But replacement wires may not have this resistance, thus perhaps requiring the replacement plugs to have 'R'esistance built in.

Everything was professionally tuned when they (Bud's) installed the PerTronix, they installed the Bosch WR7DC plugs.

The generally accepted specification for our ignition is SOLID copper core wires. Zero resistance. Not carbon core wires. The wires have Beru or Bosch metal jacketed spark plug connectors that should look something like the attached photo. As Dan Caron pointed out, these ends have resistance built in.

These connectors require that the top part of the spark plug be removed, revealing the little screw head.

Many here (myself included) chose NGK spark plugs over Bosch. I personally run NGK BP6ES. A year or two ago, we were alerted that the plug was discontinued in lieu of only resistor plugs. I went to my local store(s) and purchased 18, basically wiping out local inventory. At least I won't run out!

If I remember correctly, some owners who have owned from new have indicated that they do not have these ends, but instead a bakelite end. I recall having red bakelite plug connectors on my 1979 BMW, not too far away from a 1971 Mercedes.

That's not to say you cannot have a fine running Pagoda with something else. Many do.

[Leester]

Like Michael I was able to get my hands on a few of the 5BPES with the screw on cap and they are in the car now (with cap screwed off). I also bought some 5BPES with caps that do not screw off. I was able to adapt one, as a test, by inserting them upside down into my drill press and filing the cap down as it turned in the drill press. Tested it in the car and seems to work fine. But its a slow process, especially at the end to get the tip the right diameter - then thread it with a die so it has some grip.

I have looked everywhere for an adapter that would enable the use of these plugs with the fixed cap in our cars but they don't seem to exist. Seems like they should be easy to make. A short piece 4mm threaded rod plus the female part that attaches to the plug fixed cap.

Anyone seen anything like that? Or alternatively a 1K ohm spark plug end that fits the fixed cap spark plug.

[67230SL-Vinny]

Here's an image of my BERU ZLE121 plug wire ends. These wires are routed thru a metal channel mounted beside the valve cover.
The marking says 1K ohms, so it appears I shouldn't need the additional resistance of WR72C plugs, assuming the wires are still OK. However, the even slight brown burn color on all six WR72C plugs I removed seemed perfect. Engine compression is very good and fairly even all 6 cylinders.Cam lobes look excellent.  Factory rebuilt injection pump installed by Bud's 3-4K miles ago (8 years).
So, I honestly don't know if I'm just imagining a slightly rough idle after installing the new MB W72C plugs. Maybe I just didn't notice it before, and the only thing I changed were the plugs. As I said, the car cold & hot starts easily and pulls very strong thru the gears and hums along sweetly at highway speed with plenty of passing power.  However, I do appreciate the input and suggestions. Probably due for a good scope tune-up, valve adjustment, timing chain check.

[Peter van Es]

Please upload images as an attachment to the message. That way they'll be normal in size.

Check this thread: https://www.sl113.org/forums/index.php?topic=31410.0

[67230SL-Vinny]

OK, Now I'm reading some info that indicates because the ignition was changed to Pertronix inside the distributor, it may be a requirement to use the added resistance of the WR7DC plugs I removed.

 "Also something to consider; using resistor plugs will result in more precise control of ignition timing. The resistor act as a pressure valve and will not let the plug fire until a set amount of voltage has reached to plug,  resulting in a hotter spark at a more precise time.  With a standard plug it will spark at any time that it has received sufficient voltage to jump the gap at whatever the current conditions are."

Can anyone familiar with Pertronix electronic ignition weigh in on this??

Meanwhile, I ordered a new set of Bosch WR7DC plugs, and I may try switching back to see if the idle smooths out, as I think it was smoother before.

[Lorsar]

Where are you seeing that info?  I'd like to know because I am about to install a pertronix.

Most here will agree that our cars run better with non resistor plugs.  The pertronix installation instructions do not mention resistor plugs.  However, it does mention this

WARNING: DO NOT USE SOLID CORE SPARK
PLUG WIRE. Use suppression or carbon type
spark plug wires.
 I'm not sure this is necessary though.

The instructions also mention to check the coil if it's running rough.  Speaking from my own experience, things happen coincidentally and are not necessarily caused by the thing you just did.

[67230SL-Vinny]

Lorsar,
I'm hardly an expert, and that's why I'm reaching out to those here who are. I have read that the Pertronix units have changed in recent years, with the added warning that you mention on your new unit.

My Pertronix setup was installed by Bud's about 8 years ago. These older Pertronix units apparently would work fine with the MB OE wiring, but just required an R plug.  I trust that Bud's knew what they were doing, and I'm probably the one who screwed up by switching plugs. Like I said, when I pulled the R plugs the clean burn looked great, and I 'think' the idle was smoother before installing the non-R plugs.  -Just Say'in

I'll try switching back to the Bosch WR7DC plugs next week and see what happens. I'll probably give Bud's a call too.
If I learn anything factual, I'll post here.

[Paul99]

Someone said they cant get some NGK plugs in the USA?

if anyone needs  NGK BP6ES or BP5ES etc, they are in abundant supply in the UK.  so still available if anyone needs them

[mdsalemi]

I installed the Pertronix in my -051 cast iron body distributor in 2011. Did not change wires—running solid copper core. Non resistor plugs, the only resistance is the wire end spark plug connectors. I did change the coil to the Pertronix Flamethrower II. Idles and runs well.

[Tomnistuff]

Paul99, thanks for the NGK availability info.  Can you narrow down the source a bit?  I'm in Quebec, Canada and I can't find the non-resistor plugs either.  Where in the UK can I buy them?
Thanks.
I am currently running what is perhaps the last Bosch W7DTC Triple side wire plugs in North America that I found at a Bosch Service Center.  They were their last and are too cold.  I pass my time cleaning the soot off of them with a spark plug sand blaster.  Cold starts in Canada are not fun.
Tom Kizer

[67230SL-Vinny]

I found this quote from 2023 in another thread about Pertronix needing R sparkplugs, or not; and why Pertronix has changed to requiring carbon wires vs. copper core with their newer units. Because this was a Tractor thread, I suspect in wet applications, especially with older solid core wires there were 'spike' problems. In any case, I'm going to contact Bud's next week and ask about my 2015 install whether they suggest switching back to the WR7DC plugs they installed and tuned with the then new Pertronix.

"We're a Pertronix dealer and a few years back, Pertronix was trying to figure out why their modules were blowing out especially in Tractor applications. According to their bulletin back then, they finally figured out with quite a bit of R&D if using a solid core wire, a stray spike could blow the module out. This is when the bulletin said that anytime selling an E.I. to a customer, make sure the vehicle is NOT equipped with solid core wires. Make sure the customer installs carbon core wires which will stop the stray spikes the solid core wire can give off especially in humid or wet weather/days. From what I understand, since using the carbon core wires, Pertronix E.I. failures were cut way down big time. You don't need to run resistor plugs with the carbon wires....  HTH
Steve@B&B"

[BobH]

Paul99, thanks for the NGK availability info.  Can you narrow down the source a bit?  I'm in Quebec, Canada and I can't find the non-resistor plugs either.  Where in the UK can I buy them?
Thanks.
I am currently running what is perhaps the last Bosch W7DTC Triple side wire plugs in North America that I found at a Bosch Service Center.  They were their last and are too cold.  I pass my time cleaning the soot off of them with a spark plug sand blaster.  Cold starts in Canada are not fun.
Tom Kizer

Strange how they're plentiful in Europe, i did find these in Canada

https://www.ebay.ca/itm/285637146774?itmmeta=01HTT0PE29VST365ZV51H99QHS&hash=item42814cf896:g:MEEAAOSwUBRlli9q&itmprp=enc%3AAQAJAAAA8H%2BvJQqNAKMbbPwTlOJbzBcI3LQoLzeJVqHilC30HINjk7DYxfrRfmuIt5CDDg647TxxYK37kPlOQZevbn5obXeLco9TnPKRBA3Qvy%2Bm08Emk9W77z7rsPkXq7UL1k%2FiRkS7QuVSGnh%2FUx7ma64Qfzwzeo8Zd0nJgp%2FmshEQEA3ciuYMHCwCNUr8m0IJiW5iumXXHwPngZK8l9aH8Fet9CCC19woYVWoJfBIlDCoums%2BKu3qLgHaGpcysgIzM3L%2BvneydrXUrr%2BTVGMyLsbMZj3CputnZo8VRN%2B4BgVagLEo%2F5z7oGiOEGD41ppat6SvSg%3D%3D%7Ctkp%3ABk9SR5zh2cDWYw

[Tomnistuff]

Thanks Paul 99, for the NGK plugs-in-Canada Connection.
Tom Kizer

[Tomnistuff]

Sorry, BobH.  I screwed that communication up royally.  Thanks for the Canadian spark plug contact for the NGK plugs.
Tom Kizer