Author Topic: Spark Plug Identification for an Elmer Wall Mariner Junior  (Read 461 times)

Offline achtenhagen001

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Spark Plug Identification for an Elmer Wall Mariner Junior
« on: November 02, 2021, 10:56:00 PM »
Hello All,

Looking to see if anyone can identify this spark plug type that I have here. Any info would be appreciated and very helpful. I came across an Elmer Wall Mariner Junior engine with two broken spark plugs, one is completely sheared off and the other one has cracked ceramics. I am not sure what the thread size is. All I have to go off of are the "AC" and "3C" identification on the plug. Is that a standard CM-6 plug?

Thanks,

Marcel 

Offline stevehuckss396

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Re: Spark Plug Identification for an Elmer Wall Mariner Junior
« Reply #1 on: November 02, 2021, 11:12:13 PM »
With a caliper measure the od of the thread and report back.
Do not be like the cat who wanted a fish but was afraid to get his paws wet.

Offline achtenhagen001

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Re: Spark Plug Identification for an Elmer Wall Mariner Junior
« Reply #2 on: November 02, 2021, 11:16:39 PM »
3/8" thread diameter, thank you for the fast reply really appreciate it.

Offline cnr6400

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Re: Spark Plug Identification for an Elmer Wall Mariner Junior
« Reply #3 on: November 03, 2021, 12:34:22 AM »
It is likely 3/8"-24 UNF. This size , if I'm not mistaken, was used on many large model engines in the 1930's - 1950's. The modern equivalent of this size plug is M10 x 1.0 as used in lots of weed trimmers and some small chainsaws - but an M10 plug is about .020" too large in thread dia to fit a 3/8"-24 plug hole (unless it's really wallered out).

The other common size for model engines is 1/4"-32.

Offline Dave Otto

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Re: Spark Plug Identification for an Elmer Wall Mariner Junior
« Reply #4 on: November 03, 2021, 01:25:24 AM »
Morrison & Marvin offer a 3/8-24 plug.
http://sparkplugs.morrisonandmarvin.com/

Dave

Offline Jasonb

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Re: Spark Plug Identification for an Elmer Wall Mariner Junior
« Reply #5 on: November 03, 2021, 07:18:38 AM »
He was certainly specifying metric threaded plugs at the time, the 36cc wall I've just built an engine base on calls for 18mm spark plug thread. Is there nothing on the head drawing?

If you have thread pitch gauges it would be worth checking pitch with those but not many turns to go by.

Online Jo

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Re: Spark Plug Identification for an Elmer Wall Mariner Junior
« Reply #6 on: November 03, 2021, 08:41:16 AM »
AC is an American sparkplug brand - AC Delco.

With the early AC plugs the number designates the thread size (3 = 10mm, 4 = 14mm and 5 = 18mm)  and the letter (C) is the temperature range (how deep the gap between the central insulator and the outer metal casing is within the plug body on the sparking end).


I am not aware of AC doing imperial plugs but it is not beyond possibilities, details of these old plugs are hard to come by these days. A standard CM-6 will not have the same character as the lovely old AC plugs  :Love: so I would consider keeping them for when you show the engine.


If you buy a set of CM-6 plugs for it  :facepalm2: make sure you thread them in by hand and only tighten the last fraction using a spanner.

Jo
Enjoyment is more important than achievement.

Offline achtenhagen001

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Re: Spark Plug Identification for an Elmer Wall Mariner Junior
« Reply #7 on: November 03, 2021, 10:35:36 AM »
Thank you everyone for the helpful insights. I will see how the Rimfire V from Roland Morrison works as well as a CM-6 will do. Will keep you posted and show pictures of the final engine. Thank you again for the help, really appreciate it.