I just picked up a 75 4T 440T and am trying to replace the plugs... All charts call for a champion RJ12YC or the equivilent from other plug manufactures. They do not fit. The plug that came out was a AC R43TS. I know that is a standard chevy plug with the tapered seat. My heads also have a tapered seat. Has anyone ever ran into to this before? Can anyone help?

Thanks in advance

R1p

 

The engine is from a motorhome and is a 440-3. It uses a different plug type.

 

If they can't figure it out that way then have them cross referencce the original plug number that you took out. The autolite # would be a 25
ngk ur5 is what i came up with try and see if they fit.

 

I forgot to post the original plug numbers...
They were Champion
BL-9Y
or
RBL-9Y