We have a 1976 F100 with a 390. The manifold gaskets are going and I figure when we pull the manifolds the bolt holes will need a tap run into the holes to clean the threads. Does anybody know what size the threads are? 3/8, 1/2 13????

 

Its been thirty one years since I messed with the exhaust manifolds on an FE, but I think the threads are 5/16-18. Good luck getting all the bolts out without breaking one.

Robert

 

I'm 99.9% sure its 3/8" 16 tpi. I've only replaced about 200 hundred of em...LOL Pay a few cents more for the replacement bolts, get the grade eight bolts and coat them with hi temp copper anti sieze, not silver. The next owner will thank you. LOL

Heat the exhaust portion of the head to remove the bolt with a torch. If all else failes, get a drill motor.... I'll shut the F up now...LOL

 

The absolute best way to remove a broken bolt is weld a nut (or bolt) to the stub and back it out with a wrench. I just had a bolt broken off an 1/8th " inside the block and built it up with weld far enough to weld a bolt on it. It backed right out. You don't have to worry about catching the block with weld, since it won't stick to cast anyway.

I guarantee they are NOT 5/16" bolts. I'll go check, but I'm 99% sure they're 3/8" also. Like Riderman said, use grade 8 bolts. (gold in color with 6 hash marks on the head.) The anti-seize is a good idea too.

 

3/8-inch, coarse.

 

FE exhaust bolts...FOMOCO's darkest hour...

 

Like I said it has been a while. I do remember that sinking feeling when one of them broke off when I was changing the exhaust gaskets; and then trying to drill it out straight while the engine was still in the truck.

If you aren't using it as a daily driver, I would start spraying your favorite penetrating oil on the bolts at least a week in advance of trying to turn them.

To this day, I am leery of exhaust bolts; especially when there isn't room to get a drill between the inner fender and the head.

Robert