Spark plugs

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    My 29 had AC 77L spark plugs in when I got it. They are no longer available. Just wondering what brand and part number spark plugs others are using. I got some Motor Craft TT10 plugs from the local auto parts store but the threads on the tip of the plugs were not 8-32 like is needed to use the special brass fittings. I found out the Champion W16Y plug does have the correct threads. Any info would be appreciated


    Hi Cal,

    Champion offers a #518 spark plug which is the current version of the W18. These have the correct 8-32 threaded stud at the terminal end of the plug. However, these have about a 3/4" reach. "Reach" is the distance from the shoulder of the plug (where the gasket seals) to the end of the threads. This is not a problem for piston clearance, but some members feel that "reach", along with heat range, are important factors in achieving a smooth idle.

    Older Champion plugs, like C16C, and the old original C4 plugs had a 5/8" reach. You can sometimes still find these at swap meets or on the internet. These older Champion plugs also have the 8/32 threaded stud for the terminal.

    I am not sure what the reach is on the W16Y plugs that you found is. But these sound like a slightly colder version of the 518 (W18) Have you tried them yet?

    There are also other plugs available in Champion’s "W" series, like W14, and W10. These are progressively colder plugs, but I have not tried them.

    Autolite also makes a current compatible plug, #3076. This is also a 5/8" reach, like the old original C4 plugs. I have not used them personally, but I know that other members say anecdotally that their cars run better on the Autolite plugs. These are also available on the internet, like at, at a good price, too!

    I hope this answers your question on spark plugs.

    Happy Motoring

    Chris Diekman


    Thanks for the info. The W16Y plug has a 5/8 reach. it does have the 8-32 thread and is one step colder than the W18. they are about $6.60 a piece. I do not have my engine running yet since rebuild so I haven’t tried them. The Autolite 3076 has a 8-36 thread at the end, so the brass terminal will not fit directly. I suppose one could chase the treads with an 8-32 die and make them work. The AC plugs C77L that were in my engine also had a 3/4 reach. When I get my engine running I will have to see what happens.
    Right now in Michigan it is 3 degrees with 30 MPH winds so I won’t be driving vintage cars today!!

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