Spark plug Help

[STREETREBEL]

I bought a used 1978 440 RV engine. I went to change the spark plugs, but the ones in it shouldn't be in it. I have bought Champion 12 YC and Autolite 85 plugs but neither one will screw in. What kind of head could it have? They all have 14 mm thread. I forced one of the Champion plugs a little, but the body of the plug started to be cut by the head because it is fatter than the plug I took out.

 

[khryslerkid]

From this thread...https://www.forbbodiesonly.com/moparforum/threads/440-spark-plug-type.161006/#post-911087152

"You have the motor home heads, tapered plug, takes a 5/8" socket.

These are the 452 passenger car heads. Plugs with a ring or crush gasket. See the recess...

Here's yours...that nub is there so you don't use the wrong plug.

Double check this but I think if you look up a 440-3 engine you'll come up with the right plug. Check the thread depth before installing. Should be Champion RV12YC

http://www.sparkplug-crossreference.com/convert/CHAMP_PN/RV12YC"

 

[STREETREBEL]

Thanks. Learn something new every day.