Spark Plug Question

[BoltTurner]

Hi,

About a month ago I bought a '71 thats is in phenomenal shape. PO is an RV mechanic (this may be relevant) and took great care of it. Engine runs strong and I did a compression test today just ot be sure - all good. Engine internals are all stock - 2bbl, cam, heads, block, etc.

I replaced the spark plugs today, just to start fresh. Here's where it gets interesting - went to Autozone, they gave me motorsport plugs per their system. Got home - clearly the wrong size, computer must be wrong - diamater was way too small to fit, could praticly just drop them into the head through the spark plug hole.

Took them back, brought an original plug to show the computer was wrong. They look up an autolite plug to compare - the diameter was correct, but the electrodes were significantlly set further in (barely above the plug threads) compared to the plugs that were in there. I guess you can say the old plugs were taller. Old plugs were autolight #45. I ended up just getting new plugs that were the same as the old ones because, well, it ran pretty good before and clearly their system cant be fully trusted.

Now, given the PO took imaculate care of this truck, did all the work himself, and is an RV mechanic, could he know something the store doesnt? Or should I have gone with the plugs the store listed as correct?

 

[Broncobowsher]

The 45 plug is an 18mm thread plug. That is correct for cylinder heads up to 1974. In 1975 they changed to the 14mm thread 25 plugs.

So you have early heads, probably correct 1971 heads. The guy probably typed in the wrong year or the computer isn't programmed correctly.

 

[71broncman]

According to the owners manual as well as the Autolite website, the correct Autolite plug to use is a 124. The 45 will also work. The only difference between the two is the heat range, with the 45 being the hotter one. Hotter plug for stop and go or short trips, colder plug for heavy loads/high speeds.
Mark.

 

[BoltTurner]

Interesting. That was what the store said as well. The 124 is shorter than the 45. looks like te 45 has a power tip vs the standard. I was concerned the shorter tip would might be more prone to missing

 

[Pa PITT]

... You did correct with replacing your old plugs with the same you pulled out.
... I believe that the 45's are what I bought last saturday for my Red Bronco . I told the guy at the parts store too either give me RF14Y's Champion or cross it into Auto-light or motor craft. I believe 45's are what I went home with.

 

[DirtDonk]

Hey Curt. Welcome, and congrats on the new purchase.
Recognize your name from somewhere, but not sure if it's from here on CB (I see you've been a member for awhile) or from around town.

The plugs are probably the RV guy experimenting with extended reach tips to see if these particular heads could benefit from it. That's what I did many years ago, and have done on most of my older cars and trucks to good effect.
It was a practice racers used to work with, and also talked about by Chris Jacobs (Jacobs Ignitions) in his book if I remember.

So not a problem and I'd say you did the right thing too. Not that it would have been wrong to go with the "correct" recommended plug, but as said, if it works don't fix it!;D

If you haven't already, sign up at yahoogroups.com for the e-mail "bronco@yahoogroups.com group. That's how we let everyone in the area here what's going on, what's for sale, what's the problem, and what's for dinner.
Or maybe we've talked there or on norcalbroncos before?
Sorry I didn't see you here a couple of days ago. Six of us (including a brand new owner) met for lunch in Menlo Park on Friday for some Mongolian BBQ and Bronco-talk.

Also not pushing our stuff only%), but if you ever need anything from Wild Horses, I head over there every Monday. So free delivery to the locals.

Enjoy your new ride!

Paul

 

[jw0747]

1st big mistake..."went to Autozone." Anywhere but there.

 

[Rustytruck]

The Bronco used Motorcraft BF42 plugs in the 302 until they went to resistor plugs with the electronic ignition, then they went to BRF42 plugs. Both these plugs cross reference to Autolite 45 plugs. I always liked the Autolite 45