Spark Plugs '54 M38A1

Daddio · Post by **Daddio** » Fri Dec 04, 2015 5:04 pm

I understand the correct plug for the M38A1 is the Autolite 2245. My jeep has an assortment in the engine, the Autolite 2243 and AR8S and AR5S.

I'm having trouble with fouling in the #1 cylinder and I'll be doing compression checks and leak down tests over the next week or so. There is also an upcoming carburetor rebuild since the jeep has been sitting for the past 5-7 years.

My question is, what impact can these incorrect plugs have on proper operation. The 2243 is specified for the M38, what is different with the 2243 and 2245. Is the 2245 a hotter plug? I'm hoping the correct plug will help this issue go away.

Thanks,
Scott

Post by **wesk** » Fri Dec 04, 2015 10:39 pm

Daddio · Post by **Daddio** » Sat Dec 05, 2015 8:35 am

Thanks Wes, I'll have the new 2245s installed soon. In your experience, is that enough of a difference on the heat range to contribute to fouled plugs?

Scott

Post by **wesk** » Sat Dec 05, 2015 11:30 am

Heat range selection by the manufacturer is not usually made just considering fouling issues. Flame travel, compressions and normal internal operating temps are prime considerations.

Using a hotter plug then recommended is usually the choice made by an operator who does not want to address the fouling problem (rings etc) and would rather just treat the symptom.

As the L134 starts to age, use more oil and foul plugs the norm was to up the heat range rather then address the wear issue. The same would apply to your F134. However just using a colder plug does automatically result in fouling. If the engine is producing to much fouling materials then yes is the answer but normally the colder plug should have worked just fine in a healthy engine.

Daddio · Post by **Daddio** » Mon Dec 07, 2015 7:33 am

Thanks Wes, your thoughts confirm what i was thinking. The top half was rebuilt when we originally restored the jeep but we didn't touch the bottom half. It's never used much oil but would smoke on occasion. Historically our fouling issues have come from too rich a fuel mixture, so I'm hoping that the carb rebuild will help. I'll also be pulling compression numbers and doing a leak-down test to check the overall health of the engine

If I get bad numbers there, i'll be pulling the drivetrain for a rebuild.