The infamous Well Nut info

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Daybreak

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Howdy,

MEP 800 series generator fuel tank

Well Nut A-3816 (nitrile rubber) NSN 5310-01-197-1473 and NSN 5310-01-595-3536

It is used to secure piping on your generator fuel tank. Over time and non use they crack and break down. Or, they were overtightened. They start leaking.
Here is a new unit
A-3816 nitrile well nut.jpgA-3816 nitrile well nut 1.jpgA-3816 nitrile well nut 2.jpg

Pictures on a MEP-802A generator aux/fuel return top of the tank, and the bottom fuel drain connection.

802a top well nut.jpg802a top well nut 1.jpg802a bottom drain well nut.jpg

Here is how it mounts after being put into the hole.
A-3816 nitrile well nut 3.jpgA-3816 nitrile well nut 4.jpgA-3816 nitrile well nut 5.jpg

As it has been said, tight yes, not over tight.
 
Last edited:

Daybreak

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I have found lots of well nuts around. The problem is they have no idea what the sleeve is made of. Whether its at Home Depot, Lowe's, Ace Hardware, they could chloroprene rubber as standard. Other rubber compounds are available including EPDM and Nitrile. You want the nitrile (Buna N) because its in contact with diesel fuel.

3/8" Well Nut Nitrile (Buna N) sleeve, some permatex form-a-gasket 2 sealant for using on the threads only. The entire tank contact area should be clean and dry. and installed at 40 inch-Lbs. :D
 
Last edited:

BadRobot

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Based on the title of this posting, is it applied to MEP-804A/B as well? My MEP-804A fuel tank drain plug is leaking and I could not find a replacement part.
 

Daybreak

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Howdy,

Yes, these are made with nitrile rubber (Buna-N) and are diesel fuel compatible.

Tech Info

THREAD CLASS 2B
FLANGE THICKNESS 0.190 INCHES NOMINAL
NUT DIAMETER 0.750 INCHES NOMINAL
NUT LENGTH 1.060 INCHES NOMINAL
THREAD SERIES UNC
THREAD QUANTITY PER INCH 16
NOMINAL THREAD SIZE 0.375 INCHES
SPECIAL FEATURES SLEEVE MATERIAL IS NITRILE; THREADED INSERT MATERIAL IS BRASS
 

Daybreak

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I do not know about other gensets.

This is the part number and NSN which works on the MEP-802A fuel drain line, and the fuel return/aux fuel input line on the top of the tank.

This is the part number and NSN which works on the MEP-803A fuel drain, and the fuel return/aux fuel input line on the top of the tank.
 

Daybreak

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When installing the well nut. The area around the well nut need to be clean and dry. The only place form-a-gasket 2 is placed in on the threads. A very very little amount.

40 inch-lbs torque installation.
 

hammick

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Daybreak thanks for the great info and for selling me a couple of these. I have a couple questions though. Is the wellnut inserted from the outside of the tank? When tightening to 40 in lbs how do I keep the wellnut from spinning?

Thanks.
 

kloppk

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Yes it gets inserted from the outside. just slide it in until the shoulder of the wellnut is against the tank. You ought to by able to hold the shoulder of the wellnut until it expands a bit.
 

Guyfang

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Thanks. Any recommendation on sealant for the threads? I'm having trouble finding Permatex with PTFE locally.

Do not use any sealant. No need to, when it's installed right. Simply insert, and apply 40 inch pounds, just like DAYBREAK said. And it's a done deal.

This well nut will fit ANY MEP-8XX gen set.
 

hammick

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Do not use any sealant. No need to, when it's installed right. Simply insert, and apply 40 inch pounds, just like DAYBREAK said. And it's a done deal.
Thanks but the military instructions he attached say the threads of the "straight adapter" should be coated with "sealing compound".
 

Guyfang

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Thanks but the military instructions he attached say the threads of the "straight adapter" should be coated with "sealing compound".
The following passage is from the -24 manual. This is for the installation of parts on the fuel tank. Items 38 and 42 are the well nuts. No mention is made of sealant. EVERY other item mated to the fuel tank, uses a sealant to mate/bond the services. Only the well nuts do not use a sealant. Good, I guess you can use one, but its not necessary. I installed uncountable well nuts. I never used sealant. BUT, I did use thread tape on the well nut threads. I suppose some forma gasket 2 could be used instead.

2-83-3. Installation.
a. Install fuel level sender, paragraph 2-76-4, fuel float switch, paragraph 2-77-4, and fuel pickup paragraph
2-78-3 in fuel tank (33, Figure 2-21).
b. Install bushings (38 and (42), washers (37) and (41), and fittings (36) and (40) in fuel tank (33).
 

hammick

Member
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Location
Missouri
Thanks. I will use the gas rated threaded tape on the wellnut threads. I'm fixing the drain line so no worry of it getting in the injectors.
 
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