Spark plugs for 71 429cj.

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anderslober, the production installed spark plug in your 71 429 was a Autolite (replaced by Motorcraft) ASF-32. When the copper core plugs were released it became ASF-32C. When the platinum plugs were released as a alternative ASF-32P was the Motorcraft number. You can check this link and cross reference the Motorcraft numbers if you happen to have a favorite brand of plugs. http://www.sparkplug-crossreference.com/

 
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Autolite 45's which are an 18 mm plug work fine for me.

Adapters are available that will allow the use of 14mm plugs which opens up a whole lot more selection but for a moderately powered street car in a decent state of tune you shouldn't need to go there.

Edit: Sorry missed the CJ head part. I was assuming a regular passenger car head. The CJ heads do indeed use the 14mm plug.

 
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Anderslober, since this is a CJ style 429 that run's the ARF-32 series plugs, the "A" designation would indicate a 14mm plug. Most of the stock 429's were still running the BRF-42 with "B" indicating 18mm.

 

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