TheHaflinger.com

the cutter is a flat faced cutter , a bit like a tap / faucet reseater .
it fits in a tube that is a snug fit in the hole .
after refacing , the mushroom valve is put in a with the correct size hole in the end , and a light tap to give a new seal

kerry

The repair manual does describe how to reface the the pressure relief valve face. I would hazard a guess that it you had the oil pump in your hand that a good machine shop armed with the relevant pages from the repair manual could do the job.
The other possible options are to send the oil pump to someone like Jim (posts on here as Goatwerks) or Leo (posts on here as Puchmanlenny) - they can probably do the job for you.

John

I would have thought valve grinding paste would have also worked OK.

Garry

the valve relies on a square faced hole ,
you may succeed with valve grinding paste .
i wouldnt try it .

kerry

As pointed out, the mushroom valve seals against the "sharp" edge of the hole in the oil pump housing. This is to minimise the area that an item of dirt / metal filing can get trapped on whilst the valve is opening and closing.

If something gets trapped in the sealing zone it holds the valve "Open" and so reduces the oil pressure, this will then never recover whilst the foreign object is trapped there. A narrow sealing edge gives less chance of something getting stuck on the sealing edge than if it was wider.
Unfortunately, using valve grinding paste would "pocket" the mushroom valve into the sealing face in the oil pump thus increasing the size of the area that provides sealing.

John

I am going to fit an oil pressure gauge and determine what exactly is happening, as I have to set my idle to about 1000RPM to put the pressure warning light out, and I'm scared that even then, there might not be much more pressure than the threshold for the light. (For some stupid reason, I didn't think anything of this until I read over some of the posts here for the second or third time, and then it dawned on me that the light needs to go out immediately! I'm just used to idiot-proof modern cars)
Once I get a gauge, I can look at my options for increasing the pressure. I know for sure at least one of my mushrooms needs cutting - the round part has a score line.

i have also seen the springs located in the wrong place .
or two springs the same .
i listed the sizes earlier

kerry