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Hi:

Three of the four U-Joint plugs on our 626 have been replaced with Zerks. I can't tell from the one plug, but the Zerks appear to be 1/8" NPT.

I want to replace with plugs as per the manual. Am I correct that the threads are NPT or are then 3/8" NF?

As an aside, these Zerks have been used to grease the joints, although the manual calls for gear oil. Will I have any problems replacing the grease with gear oil? I plan to do this over time, just using gear oil to eventually replace the grease.

Thanks,

Pat

Zerks should be 1/8 NPT though they were available in other thread sizes as well; some of the old Alemite pin-type were 1/8 NF, best to check carefully when you remove them to be certain.

From my own experience with universals that should be oiled but have been greased, you pretty much have to disassemble and clean the grease from them if you really want the oil to distribute as it should. Ditto for king pins; once the grease is in there it's very difficult for the oil to get by it to the lower bearing (in the case of king pins). Perhaps if you force-fed the gear oil long enough....you might clear the passages.

1/8 pipe and 1/8nf are worlds apart.

1/8 pipe will measure about 3/8 outside diameter. 1/16 pipe will measure 1/4 OD and many times a 1/4-28nf thread is used.

Take a pic with a ruler next to your plug. It will make things easier to identify.

Blackbeerd:

kI agree that 1/8" pipe and 1/8" NF are worlds apart, however, we were talking about 1/8" NPT and 3/8" NF; not 1/8"NF.....

Pat

Yes, you're right of course. My pin-type Alemites appear to be 3/8-24.

Owen-Dyneto:

I have seen where someone has tried to put a 1/8" pipe zerk in a 3/8" NF hole......it sort of starts, then screws up the threads! (case in point, our '31 Buick Indy Racer kingpins).

Pat

What is the lead on your zerks?

1/8 pipe is 27 tpi in both straight and tapered. 1/8 British straight pipe is 28 tpi but the treads are at 55 degrees instead of 60.

3/8 nc is 16 tpi and 3/8 nf is 24 tpi.

BlackBeerd:

Exactly, and that is why when someone puts a 1/8" pipe zerk in a 3/8" NF hole it screws up the threads!

Pat

I drilled and tapped two holes, one a 3/8 NF, the other 1/8 NPT. The one original plug fit the NPT hole, therefore the original plugs must have been NPT.

The problem was that the original plug I had was too short to see if there was any taper. It is very difficult on a 1/4" long plug to see if it has 24 or 27 tpi.

Pat