3/8 pipe thread - tapping for fuel bowl

[LodiCal]

I searched the WWW for an answer, but I am still not certain about how far I should run the tap through this 5/16" bar stock. I am replacing the fuel bowl that had 1/8" pipe thread to this new fuel bowl that has 3/8" pipe thread. Do I essentially bottom out the tap in the bar stock or should I stop short a certain amount? Thank you in advance for your assistance.

 

[true temper]

About half way or maybe a little more. Tap bit and check it, don’t go too far or it will bottom out and wont seal.

 

[Seven Gables]

I’d probably put a slide caliper on the widest threads of the bowl and stop the tap couple threads shy of that width

 

[strantor]

If you don't tap far enough, you can always run the tap back in and take it deeper. But if you go too far, there's no un-tapping. I would go no further than half way, check, and go deeper if you need to. One or 2 turns at a time.

 

[Menagerie-Manor]

Rule of thumb for pipe threads is 2-1/2 to 3 turns by hand for a correctly cut thread.

 

[oldtimer 66]

To add a little information, the original female threads may have been dry seal threads. That it what we used on all of are diesel engine components. It eliminated the need for any type of sealant on the first assembly. The tapped hole is tapper reamed before tapping using the L1 and L2 gauges. This way you have full thread engagement / crest and root/ for the length of the thread.

 

[rScotty]

I'm curious why you would not simply use a brass thread adapter?

 

[LodiCal]

Thank you for the replies! It seems pretty straight forward/"common sense" like, but I just wanted to check with people who know much more than I.

It seems that I spend 25% of my time thinking about how I should do something, 25% of my time working on stuff, another 25% of my time re-doing stuff that I worked on, 25% of my time in the garage, pump house or shed wondering what I walked in there for and 25% of my time trying to figure out why my math/measurements did come out right... ;-)

rScotty - I looked at a couple of options from welding on a 3/8" fuel bung to utilizing a thread adapter. It's an old rusted fuel tank that I am cleaning with vinegar & bolts and if I used the adapter, the screen on the fuel bowl would have to be removed. I am thinking that I need all of the screen/filter I can get. I looked for a fuel bowl with 1/8" NPT to replace the one I took off, but I was not successful in finding one that had a decent review. About 40 years ago, I could go to the small engine repair place and get a gasket kit for a fuel bowl but it seems that those days are long gone at least the two local places I checked with.

Thank you again for the replies!

 

[rScotty]

Thank you for the replies! It seems pretty straight forward/"common sense" like, but I just wanted to check with people who know much more than I.

It seems that I spend 25% of my time thinking about how I should do something, 25% of my time working on stuff, another 25% of my time re-doing stuff that I worked on, 25% of my time in the garage, pump house or shed wondering what I walked in there for and 25% of my time trying to figure out why my math/measurements did come out right... ;-)

rScotty - I looked at a couple of options from welding on a 3/8" fuel bung to utilizing a thread adapter. It's an old rusted fuel tank that I am cleaning with vinegar & bolts and if I used the adapter, the screen on the fuel bowl would have to be removed. I am thinking that I need all of the screen/filter I can get. I looked for a fuel bowl with 1/8" NPT to replace the one I took off, but I was not successful in finding one that had a decent review. About 40 years ago, I could go to the small engine repair place and get a gasket kit for a fuel bowl but it seems that those days are long gone at least the two local places I checked with.

Thank you again for the replies!

Now I know why that sounds familiar. I recall going through a similar problem a couple of years ago on our1958 John Deere 2 cylinder. BTW, that task led me to find out which gasket & thread sealers that are impervious to gasoline. Many are not.
rScotty

 

[LodiCal]

rScotty, since you brought it up, I purchased Permatex High Performance Thread Sealant for both the hydraulics and the fuel system (recommended by the Hydraulics place where I purchase my seals, fittings and hydraulic hoses).

The Permatex website states the following: "Stainless steel fittings, head bolts into through holes, oil PSI sending units/sensors, oil and coolant lines, intake manifold switches, rear axle fill plug, and fuel fittings."

What were your findings in regard to thread sealers impervious to gasoline?

Thank you,