harleyKmodel

Does anyone know the flare angle used on the K Model gas tank, pet cock and fuel lines? To the naked eye old well-worn examples I have make it appear to be a relatively low angle, but could not venture a guess as to what it actually is. From recent reading I’ve done have heard it suggested that it is neither SAE (45 deg) nor AN (37 deg), but rather Harley's own angle pf ~ 30 deg. Anybody have any firm information on the “correct ” angle? Thank you.

Yes it's odd angle, and it is a special thread. Almost like they are or similar to fine sink fitting threads. Got an adapter at a plumbing store once, to fuel filter. While we are in this area, remember at carburetor line inlet the brass needle seat in rebuild kits is not drilled out to receive the K hardline. You want to do that first. Erik

EKHKHK56 wrote:Yes it's odd angle, and it is a special thread. Almost like they are or similar to fine sink fitting threads. Got an adapter at a plumbing store once, to fuel filter. While we are in this area, remember at carburetor line inlet the brass needle seat in rebuild kits is not drilled out to receive the K hardline. You want to do that first. Erik

The NOS rubber gas line in my possession (lent by a friend), has 1/8" NPT female thread on the carb end (so "yes" to your plumbing suggestion) and on the tank end has straight internal 7/16-20 thread with flare inside.

I don't think the thread is std on carb end. I'll check back...

EKHKHK56 wrote:I don't think the thread is std on carb end. I'll check back...

Erik,

Good catch. You are correct the thread is not 1/8” NPT. When I measured it originally and found it was 27 tpi I simply assumed it was 1/8” pipe (only common 27 tpi I know of) and meant to say it was 1/8” NPS (national pipe straight) like used on lamps. However, following your comment I did more measuring and found the OD of the carb seat thread is ~ 0.437”, which makes the thread a 7/16-27 NS thread, which is in fact an odd duck – exactly as you mentioned.

http://www.practicalmachinist.com/vb/general/7-16-27-ns-threads-used-what-151821/

Regarding the flare angle, I measured several complimentary male tank fittings on an optical comparator and found the angle to be 45 deg, so standard SAE flare. The picture below shows the image from the optical comparator. Not shown is the large precision lens perimeter degree scale for determining angle, but even from the coarse image it is obvious that the flare is 45 degrees.