So, ford has used emission thermactor plugs, for small block heads for many years.
These emission thermactor plugs are useful, when installing a pair of emissions legal heads, on a non-emissions engine.
So, ford designed these plugs to have multiple uses. Consequently, ford drilled and tapped a hole in both ends of the heads, for a 5/8-inch national coarse (N.C.) thread.
Emission Thermactor Plugs, also allow you to remove, the exhaust air supply rails from heads. All (OEM) and aftermarket ford smog legal heads, have thermactor holes, one on each side of the head.
So, if the engine is using emission hook ups with a smog-pump, the rear hole are left open.
These emission thermactor plugs, can do two things:
- Plug the rear holes, if you are not using any emission hook ups. Note: That the plug is internally drilled and tapped, for a 3/8-inch N.C. thread.
- Allow you to attach accessory drive brackets, to the front of the heads. ( Most accessories use a 3/8-inch N.C. bolt )
Sometimes in an emission exempt vehicle, the rear hole may be left open by mistake.
Left open, the holes will generate a tremendous exhaust leak. Consequently, sometimes blamed on leaky header or exhaust manifold gaskets. But, was actually missing, emission thermactor plugs.
So, when not using the smog pump, the O.E.M. Ford 5/8-inch blind hole insert (Ford PN 351418-S) is a simple and cheap fix to this problem.
These plugs are also available from Pioneer Engine Products, using part # PF580
So, you will be able to screw these plugs, into any head that has the holes. Consequently, they change the thread size to allow you to use, your factory accessory drive brackets. You may want to use these plugs, to close off any air passages in your cylinder heads. Because, if there were no plugs, you would have an exhaust leak.
TIP:
Now there are some cases when you don’t need, the emission thermactor plugs for brackets. You may just want to plug the holes.
You can go to your local bolt shop, and find, 4- 5/8-11 x 3/4 stainless steel bolts.
Don’t forget to use a good thread sealer, as the pitch of these bolts are quite coarse.
Conclusion
Finally, these plugs have multiple uses, but, if forgotten you may have that, unexpected exhaust leak.
BY DANNY BENDER
