Confirm fuel shut off thread size?

knightscape

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Jul 29, 2013
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Hey guys, could someone verify the fuel shut off threads for me? Both shut offs that I have for my 2 and 4 stroke kit tanks seem to be M10x1.0 non-tapered threading, is that correct? I have one valve that is similar to this one:

http://www.gasbike.net/bike-motor-part-gasoline-tank-switch-cu.html

and it seems to measure out as the M10. I'm trying to turn it 90° with a street fitting, but I can't find anything like that in M10, so that's making me question if I measured the threads properly...

Thanks!
-Sam
 

2door

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Sep 15, 2008
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Littleton, Colorado
You are unfortunately incorrect and many have problems because they don't know the difference between a 'machine thread' and a 'pipe thread'. The kit tanks are in fact 10mmX1 'machine' thread which requires a gasket to seal. Pipe threads are tapered and are NPT, (National Pipe Thread) If you're careful you can get a 1/8th inch NPT petcock to thread into the kit tank bung but you'll be lucky if it doesn't leak.

You can run a pipe tap into the bung and 'adjust' the threads to take the NPT petcock. The problem is tapping too deep and then the petcock won't seal properly.

What most folks don't know is that pipe (tapered) threads seal because of the taper. They don't typically need thread sealing compounds to keep from leaking. Teflon tape or pipe dope is often used but it is there as a lubricant to assist threading in deeper and sealing better. The tape or dope is not a sealer. If you have to seal the threads you are using a bandaid because of the threads not matching, the gasket is damaged or not there, or it wasn't threaded in tight enough.

The link you provided shows a non-tapered, or a machine threaded petcock. That's why there is that red gasket on it. The gasket does the sealing; not the threads.

Hope this dispells some myths about tanks and petcocks.

Tom
 
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knightscape

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Jul 29, 2013
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Dang, this was one time I wished I was wrong. I'm familiar with the various threading standards, just making sure I wasn't measuring wrong. It seems that a non-tapered M10 street 90 fitting doesn't exist. No way am I retapping my brand new frame (GT2a-s). I'll just make the shut off I have work going straight. Thanks for the info!
 

2door

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Sep 15, 2008
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I'd have to ask if you 're sure of the threads in your frame's tank. Is it in fact 10mm X 1 machine thread? Are you certain it isn't 1/8" pipe?
I'm not familar with that frame so I'm relying on you to determine.

Tom
 

knightscape

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Jul 29, 2013
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Yeah, it's definitely machine thread in the GT2A-S, both shutoffs I've got thread right in smooth and snug all the way to the gaskets, just like they do on the bolt on kit tanks. I should clarify: What I was hoping to do was turn it 90° to make a little more clearance by adding a street 90 elbow and the regular shutoffs I've got. I tried out a 1/8" NPT street 90, gingerly to see how much thread I could get together, and wasn't happy with the depth i could get to. It would have forced me to bung up the threads pretty bad and use a bunch of thread dope, which as you said is not a good solution. I have a feeling this is going to be the one thing on this build I keep looking at until I find a way to change it. M10x1 is pretty common for grease fittings, so I may be able to use some other parts strung together, long as I can make something somewhat graceful.

One thing I'm going to keep looking for is a 90° fuel shut off. They are all over ebay as "Generator fuel shutoffs", but they list threading as M10x1.25 rather than 1.0 ;P
 

sub66

New Member
Apr 25, 2014
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canada
yea m10x1 hose barb w external shutof/ can u get that?

mbicycling.ca has little brass shutoffs that are worth a try aswell.
 
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knightscape

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Jul 29, 2013
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Maine
I think I may have a solution: M10x1.0 turns out to be pretty simple to find in Banjo fittings (normally used in brake applications). I just need to find a decent sized banjo with a barb end for hose, then put in an inline fuel shutoff which is easy to find, and I'll be in business.
 

GearNut

Active Member
Aug 19, 2009
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San Diego, Kaliforgnia
Make it yourself brake line kits are all over the market. I am sure that you can find a replacement 10mm banjo on the 'net. The good ones are barbed, however the barb is rather small as the PTFE brake hose liner is typically 1/8" id or thereabouts. Expect to use a 1/8" fuel line to the in line filter and the usual 1/4" from the filter to the carburetor.
 

Rage001

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Jun 4, 2021
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Dang, this was one time I wished I was wrong. I'm familiar with the various threading standards, just making sure I wasn't measuring wrong. It seems that a non-tapered M10 street 90 fitting doesn't exist. No way am I retapping my brand new frame (GT2a-s). I'll just make the shut off I have work going straight. Thanks for the info!
Yeah my felt faker is straight as well its m10x1.5 pitch cant find 90 degree o e anywhere so if you found some some where need to know
 

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