C2 fuel line fitting size
I would appreciate if someone could tell me the size of the fuel line fittings that connect the carburetor to the fuel filter are for my 340 HP 63 vett. They appear to be a 1/8 inch pipe fitting with unknown # of thread to the inch. But may be something different.
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Re: C2 fuel line fitting size
National Pipe Threads are not in "inches". In fact, they are dimensionless... simply 1 NPT, 1/2 NPT, 3/8 NPT, 1/4 NPT, etc. For each NPT size there is a standard number of threads per inch. Doing a Web search - national pipe thread - will easily yield a chart with all the specifications/dimensions for each NPT size.
The fuel filter has adapters at each end. I believe the end that threads into the filter is 1/8 NPT, but it might be 1/4. The other end of the adapters that route to the carb and fuel pump are 3/8" flare fittings based on the nominal OD of the fuel pipes. Again, a Web search is probably your best bet if you want detailed specs/dimensions for standard flare fittings. There are two common families, 45 deg. SAE and 37 deg. AN (Army-Navy). The former is used for most automotive fuel and brake pipe applications. AN is used on aircraft and is also commonly found on purpose-built race cars.
DukeLast edited by Duke W.; October 18, 2016, 09:47 AM. -
Re: C2 fuel line fitting size
Duke
Thank you for the feedback. I was able to confirm that the fuel line fittings are inverted flare and with a thread file was able to confirm that these are 20 threads to the inch. At least as with what I see on the file. I had a fitting that needed cleaning and once cleaned I was able to thread into the fuel filter adapter. The 1/8 NPT pipe appears to be the size for the carb and fuel filter connection. What would be nice to know is how one might clean up threads in a fuel pump. I have two correct fuel pumps one on the car and one off. The unit that is off the car has threads that could stand clean up. Since you probably have seen this issue can you offer any suggestions for this repair. The threads do not appear to be gone but some appear rolled over.
Thanks
RichComment
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Re: C2 fuel line fitting size
I assume you are talking about the two machined female NPT threads in the fuel pump housing. If you want to clean them up you'll have to get a hold of a proper size NPT tap. I think those are 1/8 NPT, too.
DukeComment
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Re: C2 fuel line fitting size
Hopefully not being captain obvious here, but....
Note that NPT threads are tapered, i.e. slightly coned shape. The seal is in that taper interference, as opposed to sealing against an angled flare, etc for other fittings. That's why NPT connections feel so resistant to tightening compared to other threaded connections. Therefore, when cleaning up NPT threads, be aware that NPT taps and dies are also tapered, so don't get overzealous with going too deep/far as you will be removing more material than desired. Just go far enough to address the rolled threads only and hopefully that fixes the issue. You never want to "run thru" with a NPT tap for example like you would with USS/SAE taps or you will remove the taper.
If I recall correctly, the threads per inch on NPT's are purposely much different than either similar sized SAE or USS thread TPI values, to help keep you from accidentally using an SAE or USS straight tap to ruin NPT tapered threads.Comment
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Re: C2 fuel line fitting size
Thank you for the information
RichComment
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Re: C2 fuel line fitting size
Thank you Jack for the follow up information
RichComment
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