Solution: Tubeless Tire needs Valve Stem Replacement/Repair
After much research I found out that after many years rubber and metal valve stems (their gaskets) do dry rot, disintegrate and then leak air. On occasion they might pop while you are riding and cause you to crash. There are many documented cases of riders crashing due to valve stem failure, some catastrophic. As a general rule the rubber ones should be replaced every time you change your tire, resulting in a very low failure rate. If you can move the valve stem sideways in any way and air comes out, you need to replace it.
Metal valve stems do last longer but are not a permanent solution. They have rubber gaskets which, given years, also leak. Overtighten the gasket and it will leak prematurely. I'll get a 90 degree metal valve on my rear tire the next time I replace it, as it just makes checking the tire much easier.
There are a couple of DIY methods to replace the valve stem. They use large C clamps, one on either side of the valve, to compress the tire sidewall and break the bead. Compress the tire sidewall sufficiently to be able to expose and remove the old valve stem, and then to replace it with new. The tire needs to be relatively new and pliable. My valve stem is in the middle of my rim width.
I tried this with 2 C-clamps and it did expose the old valve, but because my tire is a relatively skinny 100/90/18 there was not enough space left to remove the valve. The combined thickness of the two sidewalls was thicker than the middle of my tire, blocking my efforts to remove the valve. The valve has a large bulbous end that needs extra clearance. On a thicker tire, like my rear tire, this C-Clamp methods would probably work.
I bought a
large C clamp. My 1100s valve stems were rotted.I had a feeling the stems were leaking so I put pressure on them and POP they flew off. I placed the clamp with 2 pieces of wood clampped the tire a bit. This broke the seal and allowed me to get the new valve in from behind. I didnt have any water based lube So I grabbed a tube of that intimate gel ( hey it is rubber safe) Got it in and with a pair of diag clippers and a piece of wood for leverage The new valve poped in place.
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I had a couple of 6" c-clamps and a big heavy duty screw driver.
I protected the rims with heavy cloths on one side of the rim to keep the clamps from digging in the rim. One side of clamp on the rim and the other side on the tire. Then used the c-clamp to compress the tire. I put one clamp about a foot to the rear of the stem and the other about a foot forward of the stem. Once you get the bead broke loose and the clamps pulled tight then you can get in there to seat the new valve.
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My final solution was to replace my tire and the valve stem, which I did at Snow City. I needed a new tire anyway, and replacing the valve was the same work required as to replace the tire, which cost ~$35, cost of tire excluded. They did a good job. Sometimes you can do fixes at home, and sometimes you need "Plan B". This time I needed the alternative.