Mercedes-Benz Ponton
Spark Plug Cross Reference

Introduction

The following table indicates the current spark plugs as derived from the as many as 15 Bosch plugs originally specified in the owners manuals for several Mercedes-Benz Ponton models [1]. Since the Ponton period (1953-1962) the original Bosch plug variations, with narrower, more specific heat ranges, have been replaced as Bosch (as well as other manufacturers) has broadened the heat ranges of modern plugs.

Note that the Service Manual Model 190 (SM-1207-000), as well as Harold T. Glenn's Mercedes Repair and Tune-up Guide, indicates that a second crush ring is required when using Champion plugs. Apparently this is no longer true.

All 12-volt Ponton owners manuals, except for the 180b, specify .027 inch for the gap for nonsuppression (nonresistor) [3] plugs and .035 inch for interference suppression (resistor) plugs. The 180b is different in that it calls for a gap of .035 in. for both the resistor and nonresistor plugs. Why the 180b engine is different in this respect is unclear [4]. Because there is no logical reason for a different gap on the 180b engine and based on the official table presented in the Addendum below, I have to suspect that the cited gap of 0.035 in. for the 180b is a typographical error.

Some knowledgeable sources suggest using .020-inch gap with the nonresistor plugs in the Pontons. Others have suggested that .032 inch is more suitable for nonresistor plugs. I cannot explain this difference in advice or whether the difference has significant empirical effect. I gapped my nonresistor Bosch plugs at .027 inch, as specified in my owners manual and am satisfied with their performance and appearance.

Apparently the original reason for resistor plugs was to reduce possible ignition or charging system interference with AM radio reception; perhaps short wave and two-way as well. FM reception appears not to be affected or benefited by suppression devices, including spark plugs and gaps. FM reception with my original Becker Europa tube radio is fine with nonresistor plugs. Note the discussion in section 82-21 of the 180—220SE service manual that identifies a host of suppression devices for when radios are installed [5]. Most knowledgeable sources suggest not using resistor plugs, with their wider gaps, in our Pontons today unless there is unacceptable interference in AM radio reception. If AM reception is of concern, one needs to experiment.

Some sources suggest that plugs "hotter" than what the manual specifies are better; for example Bosch W7DC, W8DC, or W9DC for the higher compression (8.7) heads, and W7BC, W8BC, or W9BC for the lower compression heads. This is due to the aging engines—oil burning and valve guide leakage, etc.—and the leisurely type of driving done with the old Pontons. The optimum heat range of plugs in a Ponton today is, therefore, best determined by what the plugs look like in service, rather than what the manual specifies for new vehicles.  Several informative websites can be found when entering "spark plugs" in to an internet search engine such as www.google.com [6].

Some Ponton owners report better experience with NGK plugs than Bosch. Others prefer yet different brands. I conclude that it comes down to experimentation. For my part, in my 1959 Ponton 220S I have installed Bosch W7DC (nonresistor) plugs gapped at .027 inch as called for in the owners manual. So far I am satisfied, but time will tell as I monitor plug appearance. I have discerned no electrical interference from these nonresistor plugs. I first tried Bosch WR7DC (resistor) plugs gapped at .035 inch as specified in the manual because of my radio, but I was slightly less satisfied with increased difficulty starting cold.

Finally, one must acknowledge the unresolved discussions among Mercedes-Benz enthusiasts and experts about the desirability of using platinum plugs in lieu of the indicated standard copper plugs. I conclude there is no absolute, definitive answer. Anecdotally, I get the sense that the majority of owners and mechanics have settled on non-platinum plugs for their 1950-, 1960-, and 1970-era Mercedes-Benz vehicles [7].

Conclusion

For those Pontons requiring the shorter-reach (1/2-inch) spark plugs, Bosch W7BC, W8BC, and W9BC (or their equivalents in other brands) should cover requirements today. For Pontons requiring longer reach (3/4-inch) plugs, Bosch W7DC, W8DC, and W9DC should cover all needs. I say this knowing that, originally, Bosch W5DC and W6DC (and their resistor and short-reach counterparts) were specified in some models' owners manuals for open-road driving. Again, one would have to monitor plug condition after a period of usage to determine whether to use a "hotter" or "cooler" plug within the above groups [8]. For me, I decided to start at the second lowest number ("cooler" end of the Bosch number spectrum) and work up from there if warranted [9].

Disclaimer

The foregoing is accurate to the best of my knowledge and is provided as a courtesy. No guarantees are offered or implied. Readers should verify accuracy before relying on the information supplied. I obtained the designations from a cross reference chart on the web, which has since been succeeded by one with less coverage. I have not compared individual plug characteristics.

Footnotes

[1] For those with Mercedes-Benz Type 300 "Adenauer" limousines: One original plug listed for Adenauers is Bosch W225T7D. That equates to current Bosch 7531/W5BC in the table. The other original plug listed for Adenauers is Bosch W260RT20 which equates to current Bosch 7530/W4CC. This latter plug’s NGK equivalent is 2511/B8ES. Its Champion equivalents are N2C and N3C. For readers wondering what an “Adenauer” is, there were the large Mercedes-Benz luxury limousines of the 1950s period. Among aficionados they are not Pontons although there is a very obvious relationship. See the Adenauer page for a more thorough description.

[2] WB7B is not generally stocked in the United States. The Bosch technical data sheet indicates it is a resistor plug with the following characteristics: gap 0.7 mm (.027 in.); metric thread 14x1.25; thread length 12.7 mm; width across flats 20.8 mm; flat seat; terminal type 5/8 in. Current Bosch part number: 0 240 235 003. 

[3] The manuals refer to “interference suppression” plugs. I think modern parlance is “resistor” plugs. 

[4] Both Adenauer plugs are reportedly gapped at .019 inch. 

[5] I could not determine from section 82-21 whether these many interference suppression devices, including plugs, were installed only in cars fitted with two-way radios or whether they were also installed in cars with regular AM, FM, SW, and/or LW reception radios. It is interesting to compare the page in the picture parts book for ignition systems with the various interference suppression devices and the page for ignition systems when these devices are not installed. 

[6] I found for cross references www.clubplug.net/cross very helpful, but recently this site changed (reportedly only temporarily) to provide less coverage breadth. A Bosch update table on the web is bmwscotter.org/topics/spark_plugs/Zuendkerzen-TYPE-ALT-NEU.pdf. One British source for old car spark plugs is www.gsparkplug.com

[7] Contrarily, because of the fuel-injected motors Adenauer 300d owners as a group may incline more towards platinum plugs. I have no indication about carbureted Adenauers. 

[8] Interestingly, the Adenauers originally seemed to require plugs rather cooler than ones in the Pontons. 

[9] Note that the higher the number, the hotter the plug with Bosch and Champion. The reverse is the case with NGK.

Addendum

Spark plug table included with a 1959 Mercedes-Benz Type W128 220SE Ponton. Printed by Daimler-Benz in April, 1960. Courtesy: Thomas Winberg / Sweden / January 2, 2007