hi im new i have a 67 mustang coupe with a 289 4V. My engine manual says that my car takes aautolite BF 42 plug. when i got them home i took out my old plugs and they were 5/8, a autolite AP 26, the new ones were about 13/16. does anyone know why?
your help would be greatly appreciated

 

You have a later model or aftermarket head. The newer ones are smaller.

 

well thanks it was driving me crazy

 

Yeah, 5 dollars to a hole in a donut says you have an aftermarket head.

 

i have the original heads but the guy i bought it from had them changed before i got it.

 

my 69 351w heads are the larger plugs.... maybe you got lucky and have a sweet pair of heads on that thing?!?!

 

will 351 heads fit on a 289 block?

 

sure will just need the bolt spacer things

 

What bolt spacer things are you talking about??

 

you dont need any bolt spacers, although properly sized grade 8 washers for all the head bolts would be highly recommended.