Pressure relief valve

[4sd911]

I bought a used 2.7 case and both the pressure relief piston and safety valves are stuck. Looking at them with a flash light is looks like there is some kind of build up around the edge of the pistons, kind of like calcium. I've sprayed WD40 in there, any ideas of what type of solvent should be used to free these?

[304065]

It's galvanic magnesium corrosion caused between the bore of the case and the steel pistons. No solvent will work, you need a chromic pickle, which is toxic and can kill you, so forget chemical means. I would spray liberally with PB blaster and use the Porsche special tool to remove them, called STP236.

[4sd911]

Should I be careful of destroying the bore? If it's not already. The spring has a whitish grit on it.

[cgarr]

That should have the pistons with the holes, see if you can hook one of the holes with a real stiff wire and work it out, maybe start with a stiff bottle brush might help too. I have had to put liners in some of our cases because the bores were so pitted they were not usable as is.

[Flieger]

I thought MgO was H2O soluable.

[4sd911]

cgarr, what type of material is used for the liner? Aluminum, Steel?

[cgarr]

Its an alum liner: