Has anybody ever seen a cracked block like in the cylinder wall? And second question...whats the best spark plugs for my 1988 4.0?? New head going on this week.

 

The first part of your question hints that this may not be such a simple question. I suspect you see a curious anomaly on your disassembled motor.

The second part of your question will bring out the brand loyalists to argue endlessly about their preferences. So here's mine: autolite.

 

Curious anomaly? No just curious. My 409000 mile 4.0 needs a head is all and was just wondering if that ever happens to these 2686 blocks. Thankyou for your suggestion of autolites..why?

 

I also use nothing but Autolite......trouble free for over 100K.

Yes, your block could be cracked at the bore.

 

Thwnkyou for a direct answer.

 

Here's a spark plug application chart for the 4.0:

 

Cylinder bore cracks may occur on the thrust side of the bore, that is, on the passenger side of the bore.

 

Thankyou..my bores are free of any "visual" cracks so i believe my cracked 2686 head is the issue. Thanks for the info