Thread used on 1/2A NV assemblies.

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Thread used on 1/2A NV assemblies.

Postby Graham » Mon Dec 06, 2010 5:43 pm

Can anyone please advise what thread is commonly used on 1/2A NV assemblies?

It seems to measure as 0.125" O/D and have 64 threads per inch.

I wish to buy a die and taps of this size.
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Postby chiefss » Tue Dec 07, 2010 1:38 pm

No one makes a tap and die this size.
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Thread used on 1/2A NV assemblies

Postby Ken McClenahan » Tue Dec 07, 2010 8:57 pm

chiefss did not explain that the 0.125 OD is much too large for 64 threads per inch. It is also much too large for a 1/2 A NV.

There is no standard thread size for 1/2 A NVs. They are generally number 1 or 2 screw size and the threads may be 56, 64, or 72 threads per inch. If you have a specific engine in mind, then somebody can provide some guidance.
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Postby Graham » Wed Dec 08, 2010 6:04 pm

The engine in this instance is a Condor Midget ignition engine from approx 1938. All the Condor Midgets that I have seen use a threaded needle but this one has a quite different spray bar with no internal thread, so must use a thimble style. At first I thought that the spray bar was not original to the engine but after a careful examination I have become convinced that the spray bar is in fact original. An OK 1/2A NV screws on with a good thread match. In order to make the needle valve in the correct style for a Condor Midget, I need to buy a suitable tap, or I am faced with making one.... Hence my posting.

All help appreciated..... Graham
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Thread used on 1/2A NV assemblies

Postby Ken McClenahan » Thu Dec 09, 2010 8:32 pm

After some searching on the internet I found that the Condor Midget has a 0.163 displacement so it is not a 1/2 A engine. This message thread is in the wrong catagory.

I also found a photo and it looks like the available thread on the spray bar is too short to measure the thread pitch with a scale.

You need a micrometer to measure the thread diameter and a thread pitch gage (I have both but I am a thousand miles away). Find a machine shop and ask them to measure the thread for you.

The most probable thread is a number 5 screw size with a National Extra Fine (NEF) thread. I can't find that on the internet but it is probably 48 threads per inch (5-40 is NC and 5-44 is NF). Lots of luck finding a tap for that size.

Your OK NV (if it is a OK) is probavbly from a OK 0.29 engine (either a Mohawk or a Hothead). The number 5 screw size is comon for the spray bar on engines in the 0.29 to 0.35 size range and I have run into some with a 48 pitch thread.
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Postby chiefss » Thu Dec 09, 2010 10:54 pm

Picture of it in American Model Engine Encyclopedia. Try the MECA for info on the engine. Anderson's has it and the price quoted is "Rare". Worth a fair amount.
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