Cheers matey that the problem am having at the mo seems ok running round town but as soon as i hit it with a long journey it seems to have no pressure after about a hour after a switch off. Only way to fix it is to take the valve out then she's ok again. So nylon valve will be on order next from SBD i think...
If you very slightly buff the standard one to make it a tad smaller it might improve it. The obvious solution to the jamming is to find out why there is swarf in the oil.
I had a problem with mine, everytime its given stacks it would jam, found to be the cheap big end bearings I used, so I changed these for decent ones, and changed the oil, cleaned the relief valve and pump bore, and never had a problem with it since.
I was also told that a nylon relief valve with a heavily scored oil pump bore will be worse than a standard item, and if I still had the problem after new bearings it would be new oil pump and nylon relief valve time.