Stan, Barry, thanks for your thoughts and comments.
Simon, thanks for having taken the time to annotate my photo.
I am considering a number of options, including buying a used "old style" pump or drilling an extra hole in the new one.
One thing is sure: I am become very proficient at removing and reinstalling a timing belt on a 928.

 

If your new pump builds up a pressure due to the lack of the missing pressure equalisation hole, then you need to purchase a special oil seal that can operate with higher pressures. The lip of that seal has a more sturdy design. This type of oil seal is used in 2-stroke engines on the crank. One producer is CFW (Carl Freudenberg) and the profile of that seal is called "BABSL" and the materiall must be FPM (Viton) There are also special seals with a PTFE lip that has a cut helix on the lip in order to pump back oil to the chamber. Good luck here !

/Tomas

 

i don't think so... if the oil can't return to the sump pressure behind the seal will build up to the running oil pressure ! With a cold engine 7... 8 bar at idle ?

 

Hi, I checked "Kundendienst Information Modell 82", on page 8 and 9 the changes are described. It says the old ones can be used in the new castings with connection to the sump, but not the other way around.(like you did)
Just sent me a message, I might be able to help you out.

Gr, Joes

 

Damn, this is a great thread.
Thank you for posting this and all the great pictures, and thanks to all the guys posting with advice and info.

 

The new style oil pump also has a "drain passage" from between the front seal and the bore for the oil pump gear shaft. Porsche "moved" the drain passage from the gear area to the small outer "oval slot", right next to the lower oil pump bolt. (Barely visible in your picture of the new body, but it is there.) They did this, because a drain back passage directly to the crankcase has very low resistance, while a drain back hole to the suction side of the pump can actually have a vacuum on it...sucking oil out from the shaft of the pump and the bore of the body.

A later model engine block has a hole (literally) in the block, lining up with that oval slot, which opens up into the crankcase.
When using a late model oil pump in an early engine (without the drain back to the crankcase), you have two choices:
1. Drill a hole diagonally through the lower cradle to allow the oil to return to the crankcase. (Basically making the block similar to a late block.)
2. Drill an intersecting hole (in the position of the hole in your early pump), which connects to the existing passage on the new pump. (The other end of the new passage in the pump will be deadheaded against the cradle.)

#1 works best when the engine is apart or the oil pan is off...so that you can clean up the aluminum chips.
#2 works best on an assembled engine.

If you need pictures, let me know. (I've got a plethora of engines apart, in various stages of rebuilding/building.)

 

Hi, I have this one from a old type pump. You can have it for free if you pay the shipping. I'm also in B.

Gr, Joes

 

The Cure !

 

Thanks to all for the advice. Indeed, using an "old" style pump solved the problem. No more leaks now. :-)
Next step: getting the idle speed right...