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Thread: Schrader Valve core thread pitch
08-17-2006, 07:29 PM #1
Hello All --
I've shop-made a leakdown tester, and would like to use the hose and plug adaptor with my compression tester, which has the same quick-disconnect fitting.
The plug is a 10mm x 1 thread, which isn't commonly available at auto stores. It's for a motorcycle, which explains the uncommonly small size. Never mind that it's 4" deep in the valve cover/head.
I'll own up that I haven't tried too hard to locate a commercial solution because, after all, how hard can this be to make, right?
The good news is that my hose/plug adaptor work great with the leakdown tester.
The bad news is that a compression tester needs a one-way valve at the plug adaptor. Typically, it's a schrader valve. I figured I'd just braze a slug of brass into the plug adaptor and thread it for the schrader core.
No dice. I don't have any taps that match the core, or thread more than one or two threads into the valve stem before jamming.
There are only 2 solutions I can think of -- single-point the leeeeetle tiiiiiiny threads (an old PM post said they are 5mm x .7 pitch) which means I would have to buy a special threading tool, or come up with a ready-made thing to use.
Turns out that bicycle tires all have a small brass body inside the rubber stem. I used a knife to cut away the majority of the rubber and a scotchbrite wheel to shine it up. A little drilling, a little filing, little silver-brazing and voila, a schrader valve in the plug adaptor! I'm pretty pleased with myself & thought it was worth sharing. Oh, yeah, and modest, too.
So, does anyone actually know what thread the valve core actually is??
08-17-2006, 08:08 PM #2
I actually made a series of Schraeder valve bodies for a project last year. If I'm not mistaken the internal thread is a #12-36. Might not be exact but worked fine for me. Found a bottoming tap at McMaster without any trouble.
Tricky part (for me at least) was cutting the angle for the core gasket to seat on.
08-17-2006, 08:34 PM #3
Schraeder valve thread is 0.305"-32TPI.
Air tank valves with pipe thread are available at plumbing supply houses for airing up expansion tanks for those who might be unwilling to chop up their kid's bike.
08-17-2006, 08:53 PM #4
I bought a cheap Schrader valve tool some time ago which combines a valve core remover, die for the outside thread and tap for the inside thread. I imagine these are still available. I doubt the tap
and die would stand up to much work, but for cutting the occasional thread in brass or tidying up existing threads it works OK.
08-17-2006, 08:58 PM #5
My local Ace Hardware has brass Schrader valve-to-1/8npt fittings.
08-17-2006, 09:24 PM #6
I recently had to make a valve cap for an air fork for a mountain bike. I was unable to locate an approprate tap. Also consider that the valve core seats on a tapered surface. I actually made my own tap by machining a .305 x 36 tpi thread into the end of some 4130 bar stock. I cut the relief for two flutes in my milling machine and ground the tip free hand to match the taper of the valve sealing surface. Remember I'm cutting aluminum here. I was surprised that it actually worked quite well for the one part I had to make. Anything more and it may have been pushing it. I'm confident there are plenty of better materials I could have cut my makeshift tap out of.
08-17-2006, 09:39 PM #7
On some of the old type 10 speed bike's Schrader valve tube had a steel core or what ever you want to caLL IT. Just cut it off and sholder it in sorry on the spelling