so, i took my spark plugs out to change them, and the new ones dont want to seem to go in, but the old ones go in and out. any ideas?

 

dont force them you can ruin the threads in the block... look at them next to each other do the threads match? Im not trying to be a smarta$$ but if they dont match then the auto parts store gave you the wrong plugs.

 

ya they look the same, the stock ones are a little bit longer than the new ones?

 

can't really tell if threads are the same by looking ,take one of the used and one of the new plugs and push the threads together to see if they mesh perfectly.

 

ya they mesh perfectley

 

Try to run them in the threads of the block by hand until they get a proper grip... you shouldn't be having any issues, post the part number and brand of the spark-plugs you got. Also fill up your signature so we can know wich engine you have.

 

2x. We could make some guesses but,.....

 

according to the guy i bought it from it has a 302, but its stamped 351 on the truck, does that explain the size diffrence?

 

yea most likely

 

whats the easiest way to tell the diffrence

 

What part number plug do you have should be like autolite 24,25,26

 

the ones that they gave me are motor craft asf 42c part number sp-450

 

Should be the same!

 

302/351 does not matter. Thread size is the same. If you were using autolite plugs, the 302 would use a 25 while a 351 would use a 24. This is the exact same plug, just a different heat range.

I do know that the plugs for the 302 explorer have a long/short thread version, but both are interchangeable.

 

Sorry, but somebody's gotta do it:
#1. Righty/Tightly
#2. Lefty/Loosey

I think you've forgotten, the plugs don't all screw in perpendicular to the block. Stick your pinky finger, or something else you can't loose down the hole, & identify the correct angle of attack for each plug.