My mustang currently has a Autolite 45s spark plugs. When I did my AOD conversion, the shop installed a stock Ford header (but not for my car, but a 302 I believe) on the passenger side to clear the bell housing. Well the header bolts up fine, but it gives you very limited access to the spark plugs for cylinders 3 and 4.

The 13/16 socket will not get in there unless it is thin walled, and barely. When I had the heads off, i ground off some of the header, but that didn't help as much as I like.

My thought was to go to the 5/8 sized plug. Champions plug for the 289 is RF9YC. It translates to, Resistor, 18mm threads, .460" tapered seat, 13/16" hex, standard projected, copper.

I searched and Champion does make a plug with .460" tapered seat, 5/8", but it has 14 mm threads. (RV9YC). I would like to replace the plugs without pulling the headers off, but finding the exact same plug specs with the smaller bolt size.

Anyone know if this exists? In a Autolite?

 

Hmmm… IIRC, the smaller plugs screw into a smaller hole.

You're probably better off attacking the offending material with a die grinder.

 

arent the 5/8 spark plugs for newer heads?

 

Yeah, I haven't seen any plugs with the .460" electrode end and smaller 5/8" socket area. Even if you found them would they be the right heat range, electrode length? I worked at a parts store for 8yrs. and don't remember seeing that big/small combo in a plug. If anything you might be able to find a spacer that allows a 5/8" plug to screw into a 13/16" hole? same thing you'd have to find the right heat range, etc. also. But again it's a work around, I'd do some more grinding on the exh. flange if you have the meat left to do it. A pic might get you better suggestions.
Jon

 

I agree with the others..Grind the hell out of the flange..

 

I pulled off the headers and replaced the plugs that way. Next time I take the headers off, I will grind more off the headers.

 

accell makes header plugs, thats gonna be your best bet