87 tbi exhaust manifold pipe plug

[Senck243]

Going over my truck and fixing all the half assed fixes that have been done. My dilemma now is the passenger side manifold. When the smog was deleted the tube out of the #2 cylinder was just cut and pinched closed. Want to plug it but can't find a plug. Seems like 5/8 od 18 thread count. Any help is much appreciated!


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[1987 GMC Jimmy]

What I would do is just take it out and to the hardware store or Home Depot and match it to a pipe plug that fits. You're talking about the big hole at the front of the manifold. That seems close, but I'd just remove what's left of the AIR tube and match it.

 

[Senck243]

Yea I did that but the threads are different that anything lowes or Home Depot has. Even tried to google it and can't seem to come up with anything


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[1987 GMC Jimmy]

Okay so I'm guessing you tried all the US standard NPT pipe plugs they had up through 9/16. What about metric? Like in the neighborhood of M18x1.5. That's the size of some oil plugs and O2 sensor plugs, I think. It'll be between 11/16 and 3/4.

 

[Senck243]

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[Senck243]

When I measure the thread count and pitch it's 18. Metric 1.5 or anything doesn't fit right.


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[1987 GMC Jimmy]

Maybe someone else will have found the solution, but I haven't undone my AIR system/switched to headers yet so I can't be sure. I've read online about it, and seems like other people have had trouble with the big hole on the exhaust manifolds, too. I saw where one guy welded something in there after he gave up, no one else that I could find posted a solution.

 

[Senck243]

Thanks. yea I couldn't find anything so I figured I would start some discussion


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[Wes]

Found this discussion here: Excerpt (which is confirmed as working)

"I saw (but also saw it disputed) through Googling that NPT 1/4 thread pipe plugs will do the trick. Is that true? What length would I need to buy, or are plugs standard length? I've never even bought a pipe plug before, so other than figuring out how to righty tighty them on there, I'm clueless. "

https://gbodyforum.com/threads/pipe-plug-size-for-exhaust-manifolds-on-305.21003/

 

[Senck243]

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[75gmck25]

I'll suggest a solution I used many years ago on one of my vehicles. It worked to plug holes for the old AIR system that had one tube per cylinder; however, they were much smaller tubes.

Find a steel ball bearing that fits into the hole without dropping through. Lubricate it very lightly, put it into the hole, and then thread in the old plug so it pushes down on the ball bearing and plugs the hole. The tube can be cut off flush with the top of the plug.

Bruce

 

[bucket]

I'll suggest a solution I used many years ago on one of my vehicles. It worked to plug holes for the old AIR system that had one tube per cylinder; however, they were much smaller tubes.

Find a steel ball bearing that fits into the hole without dropping through. Lubricate it very lightly, put it into the hole, and then thread in the old plug so it pushes down on the ball bearing and plugs the hole. The tube can be cut off flush with the top of the plug.

Bruce

You can cut down a penny also. Just put it in the hole and tighten the fitting down. It will seal against the penny real nice.

But that inverted flare plug posted right above looks like the right part to do the trick.

 

[1987 GMC Jimmy]

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So are these still working? Headers are my next project, but I wanted to delete the AIR first and give myself some working room.

 

[Senck243]

No this ended up being the wrong size.
Couldn’t find the right size. Ended up buying new manifolds and they come with the plugs in them. My manifolds were rotted by the collector.


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[4WDKC]

I used a differential plug for a dodge, bought it from the parts store on the shelf.