Holly NH thread sizes

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Model T Ford Forum: Forum 2013: Holly NH thread sizes
Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Johnson on Saturday, November 16, 2013 - 06:10 pm:

I am trying to rebuild an old NH and need to clean up all internal threads. The drain plug appears to be 9/16 X 24 ? I am guessing the gas inlet in a 3/8 pipe thread. Any help will be appreciated.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Eagle Ida Fls on Saturday, November 16, 2013 - 07:39 pm:

I believe the 9/16-24 is correct. The pipe size is 1/8-27. 1/8 " pipe is a little over 3/8".
Rich


Top of pagePrevious messageNext messageBottom of page Link to this message  By Stan Howe Helena, Montana on Saturday, November 16, 2013 - 08:32 pm:

The drain plug is 9/16 x 24; the inlet is 1/8 pipe; the adjustment rod is 1/4 x 32; the seat is 1/4 x 32 (where the needle and seat fit in) and the threads for the spray nozzle are 3/8 x 24.

I see you are new here, Bill. Welcome. You might want to use the search feature to see some of the older threads about rebuilding an NH. There should be a lot of them. The biggest thing other than a new needle and seat and making sure the shafts are pretty tight so it doesn't leak air is to make sure the idle passages are clean. You need to drill out the little brass plugs and clean the passages, then install something to block them. I've been tapping those holes #8 x 32 and using Allen type set screws to do those for years. (I see now there are some NH's on ebay bragging about using screws so you can clean the passages -- must have been a good idea)

Make sure you remove the tag and clean that passage, too or at least blow air through it to make sure it is open. Better to clean it, tho. I don't use the little pins to install a new tag or remount the old one. I use 2 x 56 brass screws. Much easier.

I bought a $47 tap for the 9/16 x 24 bottom threads last summer, used it once and have been looking for it ever since. Guess I'll have to buy another one. I dunno what happened to that one.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Smith on Saturday, November 16, 2013 - 09:44 pm:

Why not just find another carburetor that you don't have to do that to?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Johnson on Sunday, November 17, 2013 - 10:07 am:

Richard and Stan. Appreciate the info. I was way off on the gas inlet. Have ordered taps to get the NH ready to go back together. I like the idea to use Allen screws and brass screws instead of trying to make Welch plugs to fill holes. Hope both of you have a great Thanksgiving.


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