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Old 09-01-2014, 09:05 PM   #1
86c20
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air injection manifold plugs

ok so my 350 has the air injection set up and broke one of the tubes that goes to the manifold so i have a leak got the nut out of both sides tonight was just wondering if anyone knew the thread or where to get plugs so i can pass a cop with out being to loud lol, thanks mike
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Old 09-01-2014, 09:15 PM   #2
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Re: air injection manifold plugs

I've had luck with Cummins engine oil drain plugs working.
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Old 09-01-2014, 09:39 PM   #3
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Re: air injection manifold plugs

I only did it on my Ford, but it should be the same. The threads should be NPT (national pipe thread) so take the piece you removed to Lowes or Home Depot to match it up. Some auto parts stores might have NPT plugs too.
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Old 09-02-2014, 02:34 AM   #4
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Re: air injection manifold plugs

I use 1/4 in. npt plugs.
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Old 09-02-2014, 12:50 PM   #5
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Re: air injection manifold plugs

it dont seem to be npt seem metric??? its a crate motor form mexico if that helps any and this is 3/4 od like a half inch pipe
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1986 c20 "the hillbilly" 350 sm465 3.42gears 21mpg at 70mph
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197-8??? c30 "ramp truck" 454
1978 monte carlo 350 350th with 2.73 gears. no rust. sc car
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Old 09-02-2014, 02:56 PM   #6
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Re: air injection manifold plugs

I measured mine a few years ago. They were 19mm with a very fine thread and straight [not tapered]. Also the threaded hole wasnt that deep, so tapping them to pipe thread would be iffy. I would try a drain plug [Corts60] first. You need a friendly parts guy to try out the many sizes.
P.S. At the bottom of the threaded hole, the size reduces down to about 5/16 or so. You could try tapping that to a pipe plug, but I dont think there is much material to work with.
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Old 09-02-2014, 08:00 PM   #7
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Re: air injection manifold plugs

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Originally Posted by 86c20 View Post
it dont seem to be npt seem metric??? its a crate motor form mexico if that helps any and this is 3/4 od like a half inch pipe
19mm and yes the threads are straight. No idea what pitch i.e.: 1.5, 1.25, etc. This is what a cummins drain plug is.
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Old 03-27-2015, 07:04 PM   #8
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Re: air injection manifold plugs

Quote:
Originally Posted by 86c20 View Post
ok so my 350 has the air injection set up and broke one of the tubes that goes to the manifold so i have a leak got the nut out of both sides tonight was just wondering if anyone knew the thread or where to get plugs so i can pass a cop with out being to loud lol, thanks mike
Did you ever find a plug that worked in the manifolds? If so where did if find them? part # ? or who has them for sale?
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Old 03-27-2015, 08:14 PM   #9
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Re: air injection manifold plugs

well see its like this, i gave the old nut that goes around the tubing to my gf and she found a plumbing bushing that fits. it is the most odd ball thing ever. it is comp by pipe adt and it went right in. think it is 3/4 can take a pic if needed but its not pretty. but i dont care it works
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1986 c20 "the hillbilly" 350 sm465 3.42gears 21mpg at 70mph
1985 k30 "the ice cream truck from hell" no rust az truck
197-8??? c30 "ramp truck" 454
1978 monte carlo 350 350th with 2.73 gears. no rust. sc car
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Old 03-27-2015, 10:16 PM   #10
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Re: air injection manifold plugs

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well see its like this, i gave the old nut that goes around the tubing to my gf and she found a plumbing bushing that fits. it is the most odd ball thing ever. it is comp by pipe adt and it went right in. think it is 3/4 can take a pic if needed but its not pretty. but i dont care it works
Thanks for the quick reply, I'll check that out! Thank you!
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Old 03-27-2015, 10:36 PM   #11
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Re: air injection manifold plugs

Most GM AIR injection tubes are fitted to the manifolds with flare nuts which are straight threads not NPT. I always use Allen head set screws. The size I have used is 1/2 X 20 the taper of the set screw tip is close enough to the 45deg flare which lets the set screw seal at the flare not the threads. I also use anti-seize on the threads for removal at a later time.
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Old 03-27-2015, 11:44 PM   #12
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Re: air injection manifold plugs

When I had to replace the air injection tubes on my 350, we drilled the old flare nuts out and cleaned the threads up with a pipe tap. We discovered that they were a standard 1/4 inch NPS thread and dug up a straight plug tap to do the job.

A 1/2 by 20 plug would work worse than a 1/2 by 13 plug as the normal pitch of a 1/4. inch pipe thread is 14 TPI
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Old 03-28-2015, 12:08 AM   #13
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Re: air injection manifold plugs

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Originally Posted by Pampas56 View Post
When I had to replace the air injection tubes on my 350, we drilled the old flare nuts out and cleaned the threads up with a pipe tap. We discovered that they were a standard 1/4 inch NPS thread and dug up a straight plug tap to do the job.

A 1/2 by 20 plug would work worse than a 1/2 by 13 plug as the normal pitch of a 1/4. inch pipe thread is 14 TPI
Ahhh but 5/16 inverted flare nut threads are 1/2 X 20. Anyway that's what I do on my pre 81 vehicles. Now I can't really speak for newer engines. They might be metric for all I know.
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Old 03-28-2015, 07:31 AM   #14
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Re: air injection manifold plugs

here is one thing i want to ask on this. are you guys using the 1/2 on the single line air or is it on the ones with 3 or 4 lines to the manifold?? mine is single
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Old 03-28-2015, 11:29 AM   #15
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Re: air injection manifold plugs

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Originally Posted by 86c20 View Post
here is one thing i want to ask on this. are you guys using the 1/2 on the single line air or is it on the ones with 3 or 4 lines to the manifold?? mine is single
Sorry I was talking about the standard four tube AIR rail to exhaust manifold.
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Old 03-28-2015, 01:02 PM   #16
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Re: air injection manifold plugs

Quote:
Originally Posted by Titomars View Post
Most GM AIR injection tubes are fitted to the manifolds with flare nuts which are straight threads not NPT. I always use Allen head set screws. The size I have used is 1/2 X 20 the taper of the set screw tip is close enough to the 45deg flare which lets the set screw seal at the flare not the threads. I also use anti-seize on the threads for removal at a later time.
I cut the air injection tubes and used a 22 mm to remove the them.
It looks like fine thread . An earlier post, Someone posted they used 19mm oil drain plug from Cummins diesel . Does anyone know year make model plug is from? Or if any of you can point out the plug I need would be very helpful . Thank you!
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Old 03-28-2015, 01:10 PM   #17
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Re: air injection manifold plugs

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Originally Posted by Corts60 View Post
I've had luck with Cummins engine oil drain plugs working.
What year , make , model did you get the Cummins engine oil drain plug from?
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Old 07-13-2021, 12:40 PM   #18
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Re: air injection manifold plugs

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What year , make , model did you get the Cummins engine oil drain plug from?
Bump. Anyone have an answer to this?
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Old 07-14-2021, 07:39 PM   #19
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Re: air injection manifold plugs

Been a long time since I worked on this stuff, but try buying one of these and see if it works.

M22x1.5
https://www.napaonline.com/en/p/NDP7...&gclsrc=aw.ds&
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Old 07-15-2021, 09:03 AM   #20
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Re: air injection manifold plugs

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Originally Posted by Corts60 View Post
Been a long time since I worked on this stuff, but try buying one of these and see if it works.

M22x1.5
https://www.napaonline.com/en/p/NDP7...&gclsrc=aw.ds&
Thanks! I grabbed 2 at the parts store and the fit perfect, . For future questions on this matter, the part number is Dorman 652886.
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