Why can I not patch this tube?
Patching an inner tube is a simple process. Or at least it should be. I have a tube with the tiniest pinhole puncture that simply won't reseal. I've tried patching it several times with a proper patch kit, with the same result: the air pressure simply blows a hole in the patch. Having run out of patches, I cut up an old inner tube. The 'patches' that result from this are thicker, but just won't seal properly- air always leaks out from somewhere.
I've patched tubes before, and tried every conceivable method on this one with no effect. The hole is on the inside of the tube, so I've inspected the rim and found nothing that would repuncture the tyre. I'm loathed to buy a new tube for the sake of a pinhole, so what exactly am I doing wrong here?
The only thing I can possibly think of is that the tube may be too small for the width of the tyre: the tubes are marked 26x1.5/2.1 and while the tyres are 26x1.9, the tube is on the skinny side. Is it possible the tube/patch is being overstretched as it's inflated?