Fitting spec on air pump lines into exhaust?

[Mastiff]

Anyone happen to know? Is it metric, pipe thread, tapered, whatever? I have some caps plugging these ports now, but I don't think they are quite right. Kind of loose and rely on sealant which burns off. Maybe if I get the right plugs I won't need sealer.

 

[diesel4me]

They usually are 1/4" STRAIGHT pipe thread...1/4" NPT pipe plugs fit in the manifolds and are tapered threads,they usually seal up OK,but if not,you might be able to find ones with straight pipe threads,or improvise another method,like cutting the original emission lines off at the fittings and weld or braze them shut...some later engines may have metric threads on those fittings...I have drilled the threads out of a few manifolds and re-tapped them for bolts on a few of my trucks ,I used a copper washer under the bolt heads for a airtight seal...

 

[Mastiff]

Thanks. I went to O'Reilley and eyeballed 1/4" also. They only had one choice and I took it. These are copper. I can't tell if they are really well sealed or not, they didn't go in very far, but I think it might be because the deeper threads have been unused for years and are rusty. Any idea what the real thread specification is? I'm a little confused about how these things are 1/4". In reality they looker closer to 7/16" or something. I'm wondering what size tap I might run down there to clean up those threads.

 

[TerryD]

Best I remember they are 1/4" tubing nut threads, not pipe. They should thread in fairly easliy and seat against the tapers seat in the hole to make a seal. Are you sure your plugs are copper and not brass? I've never seen copper stuff like that.

 

[imiceman44]

Best I remember they are 1/4" tubing nut threads, not pipe. They should thread in fairly easliy and seat against the tapers seat in the hole to make a seal. Are you sure your plugs are copper and not brass? I've never seen copper stuff like that.

I am sure he meant brass, lots of people confuse the two, I know I did untill I started recently doing a lot of scrapping, it's engraved in my brain now.
Brass is the best to use in this situation, it conforms to the shape for a great seal.

 

[Mastiff]

Yeah, brass. It's easy to interchange the two.

So, what size tap? I think they aren't seating because the deeper threads are rusty and rough. I previously had short plugs in there that I tried to seal with ultra copper. Exhaust has been having its way with those threads for 10 years.

 

[diesel4me]

1/4" pipe thread is actually closer to 9/16" or 14MM in actual "size"...I have screwed 1/4" pipe threaded air chuck fittings into spark plug holes to pressurize the cylinders to do valve stem seals before,as long as you do not tighten them up too much there is no need for an "adapter"!...finger tight is good enough....I'm not sure what actual size & pitch 1/4" pipe thread is...but the 1/4" refers to the inside diameter (roughly) of the pipe fitting,NOT the threads.....................................................................................................................................................................................................You can use a 1/4" NPT pipe tap to chase the threads in the manifold and allow the pipe plugs to go in deeper --I'd re-tighten them after the engine was run awhile,as the manifold will expand a lot and they might loosen up and come out eventually if you dont..............................................................some emission tubes didn't have 1/4" SPT threads,some had larger metric ones,on those I re-tapped the manifolds for 5/8" fine threaded bolts and used copper washers under their heads...