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 ?