1/8 NPT zerks

[Ford850]

I'm trying to replace a couple damaged zerks that are 1/8 NPT. The threads on the original zerks are obvioulsy tapered, but when I try to fit the new replacements they only turn in 1/2 turn and then are tight. I've forced the new ones in a turn or two but this does not seem right. They are literally hanging on by a thread. I verified the hole thread size by using a 1/8 pipe plug and it fits perfect. Are the new zerks made THAT much oversized that they have to be forced in to size them? I've bought 3 packs from 3 sources so far and they are all the same... very little taper to the threads (if any). A NPT standard is to turn in 3 turns by hand then a few more turns to snug the threads. Has anyone else had this problem? Am I being too soft with them and need to stick a socket on them and squish them home?
Thanks.

 

[3RRL]

I've experienced what you are talking about.
I run them in with a socket but don't go too tight or you can twist them off easily. Is there room for them to sit up a little more than the old ones? If so, that is good enough. If not, get an NPT tap and cut/grind the leading end off so that you are tapping with the larger part of the taper if the pin is still in. If you can get the pin out, that would be better then you don't need to grind off the tap.
Watch out for chips.

 

[Ford850]

Thanks Rob. These zerks are centered on the front axle pivot point, one facing the front and one facing rear. There is no problem with having room for them to stick out, so I will give them another turn or so and that should be good. If they twist off I have easy access to them to get them out. Hopefully that will be fine and I won't have to use the tap to open the holes any. I hated to see them hanging out so far if there was a solution or source for better quality zerks.

 

[Soundguy]

Ditto what 3rrl said.. i like to chase most holes befroe putting the zerks back in.. etc.

soundguy

 

[Farmerford]

McMaster Carr has a special tapered pipe tap with a much shorter chamfer to accomplish the same thing as a ground off tap. It is hard to start tapping with it, but if the hole is already tapped with a normal tap it works very well to open the outer two or three threads in even a shallow hole. When I bought one I never thought I would use it more than a couple times, but I was wrong. I probably use it most when the threads in a 1/4 x 28 hole are damaged or when the 1/4 x 28 thread (it is supposed to be a special SAE taper) does not seal well, and I want to tap the hole to 1/8 NPT. It saves having to pull the pin most times on backhoes, etc.

 

[Soundguy]

Blind or Bottoming tap?

soundguy

 

[Ken Cunningham]

I wonder if the zerk would screw into a die far enough to taper it? Worth a try.

 

[Soundguy]

I doubt it..

soundguy

 

[scott_vt]

I wonder if the zerk would screw into a die far enough to taper it? Worth a try.

Good Mornin Ken,
I think Soundguy is correct, the hex would hit the die before you could get any additional taper on the thread ! Actually they make what is refered to as a GO/NO GO gage, when the gage is threaded into the NPT threaded hole it is tapped to the correct depth when the ground flat on the gage aligns with the outside surface !

 

[Eagleview]

Are you sure the holes are not metric and the plug you used is not also metric ?

 

[kc5gxc]

I have a Ford New Holland 1715. 1996. The grease zerks are not metric, not SAE, but a European thread. I had to go to the New Holland place to buy one after trying the other kind I bought at the auto parts place. The correct threaded one fit right in. They will do anything to get one into the tractor parts places....ha ha ha!!!!!!!!!!
Pete

 

[Ford850]

Are you sure the holes are not metric and the plug you used is not also metric ?

Some of the zerks are listed in the parts diagram as 6mm. The two I am replacing are listed as 1/8 NPT on the diagram. The pipe plug I have is indeed 1/8 NPT, but I realized when reading this today that I did not test it as I originally said. I compared it to the zerks and it 'looked' perfect, but layed it on the bench where I found it this morning. So I tested the pipe plug in the holes and it does NOT fit any better than the 1/8 zerks. I need to get a tap to see if it spins in partially with my fingers, telling me the thread size is correct but that it needs to be cut deeper. I already bought metric zerks to test and they do not fit at all.

 

[Soundguy]

You need to invest in a couple sets of ID thread gauges.. they are little feeler looking things.. just fold them out and test... sure beats the guesing game you are playing.

I have a sae and metric ID and OD set, as well as a bolt, spark plug, rod gauge as wella s machine screw.. etc. That and a good mic.. and you really take the guessing out on most projects.. unless you run into British thread or something like that..

soundguy

 

[Farmerford]

Soundguy:

I just saw your May 21 question to me. The pipe tap for shallow holes is called a "short projection" tap by McMaster Carr. I have not counted the chamfered threads, but I think there are more than on a bottom tap, but fewer than a plug tap.

McMaster Carr also has British Pipe Thread grease zerks which are common on Asian machinery, and DIN grease zerks that appear on German and some other European machinery.

If I recall the US 1/8 NPT is 27 tpi and the 1/8 BSPT is 28 tpi, and the thread major diameters are very close, so the two types will screw together, but they will leak both oil and coolant, even with lots of Teflon tape (don't ask how I know).

With the right attachments, one can probably have at least four different size grease zerks, of which one-eighth will leak, one-eighth will not take grease, one-eighth will be accessible only by taking off another part or turning the rig upside down, and one-fourth will get stuck on the gun tip so hard that you pull them out.