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??
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.
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.
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.
My local Ace Hardware has brass Schrader valve-to-1/8npt fittings.
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.
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