307 Oldsmobile air tube plugs

[Vicente]

Does any one know the size for the inverted flare air tube on the heads I found 4 different sets trying to find out which one to buy?

 

[olds307 and 403]

Pretty sure it is the 3/8"-24. I was lucky enough to have factory ones from my Canadian 81 Delta 88. Exactly like that except they had nipple to go into the injection hole where the inner tube is in the head. I didn't realize there were tubes in ports so I ground them off. Remove the tubes in heads before installing the plugs.

 

[Vicente]

After measuring threads per inch and using a dial caliper I found the size is 1/4-19 bsp I had tap the threads to clean out the rust and the air tubes will bolt back up but I used plugs

 

[69hurstolds]

Might be. I never needed to find plugs. For general knowledge- Just know they are NOT pipe threads. They're more like the type on brake lines. The nut pushes the flare fitting tight to make the seal. If you buy brass fittings even if it's not exact, the brass will deform before the cast iron in the head if there's any thread issues, so there's that.

 

[olds307 and 403]

Yeah, I never had to figure it out either. My 81 Delta 88 with an Olds 307 came with factory plugs, had kind of a nipple end. Factory Canadian non CCC without air injection. When the timing chain skipped at 450,000 km in my 78 1/2 ton, I swapped them over to a 83 307 and those heads later went on an Olds 350.