jwillman

I am needing to pull the oil pump to inspect and while I have it out was going to replace shaft seal and o-rings.

My plan was to pull the pump off my spare M28-16 engine (81 auto), fix it up and reinstall into my eninge on my 79.

WSM shows a PN difference as confirmed by the 928 INTL site and a call to Roger.

Whats the difference and are they interchangable or not?

Thanks.

brutus

Not a good idea. Changes in the oil relief flow at the back of the pump can cause the front oil pump seal to blow out in a rather dramatic fashion as I recall. It has been discussed before.

IcemanG17

The difference is the width of the pump, Porsche made a change to a slighter wider (21 vs 23mm I think) pump to increase oil pressure at idle....or at least thats what I recall the service bulletin said....its in the WSM and the old pump can be swapped for the newer design no problem....

Vilhuer

There were at least four changes done to oil pump setup over the years.

1. '80 MY pump housing material was changed to Alusil. Earlier pumps were gray cast.

2. '82 MY return hole was added to engine block and pump was modified at same time. Old style pump can be used in these engines. New style pump cannot be used in '78-81 MY engines. They will bolt right in but might leak from seal.

3. '83 MY pump drive gear was changed to light alloy. This requires 16x1mm shim between gear and pump shaft.

4. '85 MY pump was widened from 21 to 23mm. New style can be used in '82-95 MY engines.

Bill Ball

Erkka: I don't know how you keep all this straight. I reviewed this a couple of years ago, but I couldn't tell you a thing about it now. Good stuff, as always!

jwillman

Thanks Bill.

I don't see any of this in the WSM PDF copy. I will have to look on the Mourehouse CD.

So I have a M28/16 spare engine which looks like it was used for MY81 and 82 based on engine serial number - need to look.

If it is an MY 81 sounds like I could use it but not sure there is any real advantage. Is there any performance enhancement gained by the move from cast to Alusil?

If its a MY82 then it might have the added hole which would make it unusable, correct?

GlenL

You can use the later pump ('82+) to an older block by drilling a small hole through the block for the drain back. I did this to my '80 block and it works great. Check the pump body to see where. The hole goes in at roughly the bottom and needs to angle towards the crank and down to empty into the pan.

The original pump design applied a vacuum to the seal and could suck air into the oil.

IcemanG17

VERY interesting....... I will have to check the part number on my pump, but I would guess its an 81, like my engine is?