Ah, you noticed one of the outstanding jobs . A previous owner fitted a TR13 tube and the wheel is designed for a TR15 tube. The inevitable has happened and the valve has disappeared into the wheel. It goes against my religion to put a sharp instrument through a good tube in order to get the tyre off so I have been waiting a couple of years for it to slowly deflate, then I can get the tyre off without damaging the tube. We are planning a tyre day soon which will see new tubes for the rear tyres and the tri-ribs installed on the front. The existing rear tubes and front tyres will be fitted to another tractor.
Iain