Head plug sizes

Duramaxed

Duramaxed

New member
Ordered a pro max 6.7 head and was curious what size the two threaded plugs where that are located where the thermistor housing is. One on side looks the be 3/4” and underneath one is bigger, 1” maybe, if anyone knows where to order or the exact size/thread pitch I’d appreciate it.
 
3/4 inch pipe. The one right in the side of the head (thermostat housing area) is actually a threaded metric plug with an o-ring. M22
 
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Just a update, the underside hole is a 1” npt, the same same size as the two large plugs on the back of head toward firewall. I’ve ordered just a m22x1.50 plug as I’m
Not ready to spend $125 on a plug from Cummins lol. But if it leaks it doesn’t work I’ll have to bite the bullet of course.
 
Duramaxed said:
Just a update, the underside hole is a 1” npt, the same same size as the two large plugs on the back of head toward firewall. I’ve ordered just a m22x1.50 plug as I’m
Not ready to spend $125 on a plug from Cummins lol. But if it leaks it doesn’t work I’ll have to bite the bullet of course.
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You are mistaken. They really are 3/4" NTP.

3/4" NTP physically measure 1.05", so let me know how that 1" pipe plug fits when you get there.

I'm not looking at a Promax head, and it seems they may use their own casting, and if that's the case it's possible that I'm wrong.
 
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Snedge said:
You are mistaken. They really are 3/4" NTP.

3/4" NTP physically measure 1.05", so let me know how that 1" pipe plug fits when you get there.

I'm not looking at a Promax head, and it seems they may use their own casting, and if that's the case it's possible that I'm wrong.
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Right I’m not saying you are wrong at all, I was just posting incase anyone else came across this. I got a 3/4” plug and it was to small, Just curious what does it say the plug size is for the top two? Here is a pic
efdeb0e12ac6698c5713148ef5a0d559.jpg
 
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Same. 3/4".
I suppose they have thier own casting, or modified an existing one.
I'm just going off of Cummins published information, and there are no 1" pipe plugs in any ISB head design. I went a few more steps, and visited the Pro max site where I was able to reference the Cummins part # they show for the 6.7 head (3977225). If I input that number in Quickserve, the diagram calls for 3/4". It looks like I can be of no use here.
If I were you, I'd contact Pro max for the answers. I do apologize sir in leading you down the wrong path.
 
Snedge said:
Same. 3/4".
I suppose they have thier own casting, or modified an existing one.
I'm just going off of Cummins published information, and there are no 1" pipe plugs in any ISB head design. I went a few more steps, and visited the Pro max site where I was able to reference the Cummins part # they show for the 6.7 head (3977225). If I input that number in Quickserve, the diagram calls for 3/4". It looks like I can be of no use here.
If I were you, I'd contact Pro max for the answers. I do apologize sir in leading you down the wrong path.
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You are correct sir, I contacted them and they sent me part numbers for them and it’s exactly what you stated. Only thing I can think of is when I got the “3/4 inch” plug was actually a smaller one in the wrong box I assume. Part numbers he gave me are o Reilly’s #’s and he said that’s what they use. Again appreciate you taking the time to do research on this!
 
Duramaxed said:
You are correct sir, I contacted them and they sent me part numbers for them and it’s exactly what you stated. Only thing I can think of is when I got the “3/4 inch” plug was actually a smaller one in the wrong box I assume. Part numbers he gave me are o Reilly’s #’s and he said that’s what they use. Again appreciate you taking the time to do research on this!
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Not a problem at all. If I can help, I try. Thanks for verifying that I was on the right track, I'd hate to think I was wrong, let alone admit it. LOL
 
Just for reference, a quarter will not quite go in a 3/4" NPT hole.

The drain plug on 1994-2002 5.9's is M22-1.5. Not saying it will fit your application, just giving you a reference for the thread size and pitch. O'Reilly's would have it in the Dorman line.
 
BigPapa said:
Just for reference, a quarter will not quite go in a 3/4" NPT hole.

The drain plug on 1994-2002 5.9's is M22-1.5. Not saying it will fit your application, just giving you a reference for the thread size and pitch. O'Reilly's would have it in the Dorman line.
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That’s exactly what pro max said to use lol. It is the drain plug for them, dorman brand.
 
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