on my T1 engine both the oil pressure relief and control valve pistons are jammed. any suggestions on how to remove them?(explains why the oil cooler is now leaking).

10 mm tap screwed into it and pull valve out...

Hi

I did see a special tool to do this once, it fitted into the underside of the valve, then you expanded it. The tap will work, but it can be a pain getting the tap to grip as the valve will spin in the case.

Steve

used a 12mm tap on one valve , finally came out, the other is still tight and slightly larger than 12mm. even ran the engine with the springs removed and they didnt bugde.enough oil pressure to burst a new oli cooler but not to move the valve.

you can usea flat blade screw driver as well
jam it in n turn to break the piston loose