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mlander

SPARKPLUGS

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Does anyone have the type, make and information on the original sparkplugs used on the Mercer T head Raceabout. Information such as the diameter of the threads 7/8?-18 or 18mm plus the reach, believed to be a very long such as 1.125? (1-1/8?) or longer. Were they Champion, AC or what? Donald McKinsey seems to think they were either Stitt #19E or Champion #36. I have him sending me a Champion # 3Com but I don?t believe it has a long enough reach. This information is for my drawing of the proper sparkplug for this unusual engine. Also what may be interesting to me is contained in the question, ?Have any of the people who own or work on these engines ever measured the actual dimension of the cylinder where the sparkplug is inserted??

The ?Reach? is nominally the distance from where gasket sits on the sparkplug to where the thread ends, however being only a nominal dimension some of them are measured from the area on the sparkplug gasket sits on the sparkplug to the end of the sparkplug where the combustion chamber starts. See sketch at attachment.

Some of the sparkplugs being used in many old engines are too short on the Reach and the sparkplug is running too cold because it is not being ?scoured? by the combustion gases.

If the actual dimension on the engine measures .960? the ?Nominal Reach? of the sparkplug must measure 1.000?. This .040? difference is due to the crushable gasket after being torqued down properly.

M.L. Anderson <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" />

http://www.hatraco.com/Manufact/Champion/Brochures.htm

Then click on brochures.

7/8?-18 ALL..PLUG TYPE.. REACH......... HEX.............. PRICE EACH

510............... W10...............625?.............15/16?...........$6.51

569............... W14...............625?.............15/?6?............ $6.51

561............... W16Y........... .625?.............15/16?...........$6.51

518............... W18...............625?.............15/16?...........$6.51

520............... W20...............625".............15/16?...........$6.51

228............... RW77PP........1.000?...........15/16?...........$46.52

201............... W77N.............625?.............15/16?.......... $18.15.......... 4 GROUND ELECTRODES

539............... W77N.............625?.............15/16?...........$18.15..........?

631............... RW78N...........860?.............15/16?.......... $32.00...........?

553................RW80N..........625?.............1.000?.......... $32.00.......... ?

200............... RW80N...........625?.............1.000?.......... $32.00..........." ?

1207..............RW80PP........625?.............15/16?...........?

580............... W80N.............600?.............15/16?...........$18.15..........4 GROUND ELECTRODES

202............... W80N.............600?.............15/16?...........$18.15..........

582............... RW82P...........625?.............15/16?...........$52.98..........

559................RW83F..........625?.............1.000?...........$39.36.......... 3 GROUND ELECTRODES

545................W85N............600?.............15/16?...........$18.15...........4 GROUND ELECTRODES

203................W85N............600?.............15/16?...........$18.15...........4 GROUND ELECTRODES

589................W89D............625?.............15/16?...........$7.99............ PROTRUDING NOSE

595................C95F..............625?.............1-1/8?...........$23.29...........3 GROUND ELECTRODES

562................W95D............625?..............15/16?..........$15.55...........PROTRUDING NOSE

513................C97B............1.250?............1-1/8?...........$33.88..........2 GROUND ELECTRODES

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Quote from 1937hd45

I don't know the answer to your question, there were far more plug sizes available

in the day than we have as new replacements.

If you take a good look at the sparkplug on the left of your picture you will see that the lower portion

is almost visually identical to the one that I made the sketch on the right hand side of my sketch.

The only part that is really important is the lower portion, as the old sparkplug is a take-a-part which

is likely older than I.

I have slightly changed the sketch of mine and show the important 1.250? dimension of the right hand

sparkplug. That has to be an old sparkplug as it appears to be a mica insulator. The other sparkplugs

are not of interest to me at this time as I am trying to see/find the type of sparkplug used on the Mercer.

I am also interested in the use of this particular sparkplug.

You are correct as to the disappearance of 7/8?-18 plugs and this is why this may be of significance

to Antique car people!

#1. Is this a 7/8?-18 thread sparkplug?

#2.Was it ever, to the best of your knowledge, used in a Mercer ?T? head engine?

#3. Can you measure the 1.250? dimension to 1/32? as this is of up most importance to me and possibly

to others! See new attachment!

#4. Can you carefully look at the part and convey to me any significant Alpha/Numeric marking on it.

Yours, M.L. Anderson

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