aussie944cab

After trying to find the O ring size for late one piece OPRV, (part no. 999 707 144 40) I bought a couple and took some measurements, so here for anyone looking for the info, here are the dimensions,

OD 16mm

ID 12.4mm

Thickness 1.8mm
after checking, there are two O ring sizes, one which is correct, the other should be OK
1.78x12.42mm
and
1.8x12.5mm

Dan Martinic

Thanks for posting. Are you changing the inner one too? I understand there's some confusion about taking it apart: one Porsche service bulletin describes a procedure but another official document suggests it not serviceable

curtisr

Rebuilt and installed the OPRV from my '87 924s today. This is the second time. After experiencing super-high oil pressure (150)and subsequent leakage (!!!) from the valve cover and oil filter, I made my first attempt at resuscitating it with generic O rings. While there was an improvement (90) the oil pressure was still too high. Used the correct sized rings today and noticed that they were a bit thinner. Hope it solves the issue but won't know until the valve cover gasket is replaced which will be done as I redo the TB et al.

aussie944cab

With my basic understanding of hydraulics, the oil pressure is controlled by the plunger (valve) at the end of the OPRV (not the spring between the two sections), the o rings only seal the OPRV against the crankcase orrifice and the internal one keeps the two sections coupled together with a bit of play so as to allow for alignment variation,
This is my understanding, I could be wrong

curtisr

Thank you for the insight. The only real advice I had to go on was that the alignment tool -- supposedly to be used only in the case of installation of the air/oil separator -- should be 'installed' with finger-tightness only and, as a result, this would be the case for the OPRV as well. Were this not the case the OPRV would likely bind. I checked the plungeability (is that actually a word?!) before re-installing it. My fingers are crossed but there is no oil in the engine given the removal of the valve and plans to put a new valve cover gasket in over the next few weeks. Will update.

curtisr

'High' oil pressure reading solved! It was out with the electronic oil pressure sending kit that I had recently installed and in with a new Bosch Sport set-up. What should have tipped me off was the maximum reading the (former) meter can show was 120 psi. Had I known that was the case, the 150 reading would have put me back on the right path. Thanks everyone for your help and patience. I now vow to read all of the product literature for such things.