2 part post, start with 454 carbs

[tonyiiiafl]

My 390 has 454 Carbed engines. The starboard is newer with 125 hours. Been about 4 years and I am ready to replace spark plugs. NOT. lot of room in there. They look OK from the outside,. I came back from a 50 mile trip and sprayed some WD40 (ll I had) into the area of the spark plugs, hoping s it cools it will draw the WD into the plug thread. Do you change hot engine or cold? Keep in mind the are on the outside of the engine will roast your arms if you get them on that manifold. Suggestions? Should I be concerned about snapping one off in the head?

[Viper]

No need to remove them with a hot engine. Just keep the socket/ratchet at the same angle as the plug and you should be okay. It is tight but there is enough room to do it. Getting in front of the engines helps with the forward outside ones. If you can't get in front of the starboard engine (nearly impossible on some of those) you can do it from the top. It might take some force if they're corroded in but they should snap free. If you find yourself having to use excessive force, stop and hit them with penetrating fluid and try again later. Even squirting a little diesel onto the threads and letting them sit overnight helps.

[tonyiiiafl]

They don’t look corroded or rusted so it may not be as bad as I am making it. Agree fully on keep the angle as straight as possible. Thank you

[buster53]

WD40 is ok, but get a true penetrating oil, like PB Blaster or maybe Liquid Wrench. Spray everything and then run the engine. The vibration helps the oil soak deeper into the threads.

[km1125]

If they don't loosen right away, then try and tighten them JUST A VERY TINY BIT first, then try and loosen. That always helps with corroded bolts

[RobGunn]

BP Blaster is the best penetration oil I have ever found. I would also suggest that you use a 6 point socket rather than a 12 point. A 6 point gives a MUCH better contact on the hex of the plug.