Test of oil pump

Sigurd · 08-30-2009, 02:06 AM

Is there a good way to test the performance of the oilpump, prefarbly while still in the car?

I have a rebuilt 2.7 litre with low oil pressure, a little over 2 BAR @ 6000 with a warm engine. Double checked with a mechanical gauge. The pressure during warm up is higher, 4 BAR @ 3000. The results are the same with 10W-40 and 5W-50 oil.

As I see it there are three probable causes for this; either high bearing clearances, an oil pump problem, or a pressure regulating fault. I am trying to diagnose as much as possible before I open the engine again.

The bearing clearances were not properly measured during assembly. However the machine shop measured the block, the rods, and the crank and reported them to be within spec. My fault for not controlling the final clearances myself.

I do not know the history of the oil pump, as the engine was purchased as pieces of parts. The gears looked ok with no scars etc. Will measuring the pressure in the port where the pressure regulating valve is positioned make any sense?

If I get another, prefearbly a four rib pump, how can I make sure it is OK before installation? I have found no wear specifications anywhere.

As for regulation, both springs and pistons are new. It performs the same with both the old and new spring legths. It is a replacement block, no type or serial number, made in 79.

Any advice on how to check the performance of the oil pump is greatly appreciated.

304065 · 08-30-2009, 04:49 AM

Sigurd,

You say, "it performs the same with the old and new spring lengths." Without executing the oil bypass modification, the "new" spring length is not correct. The "new" spring is intended to be used with the "new" piston and the "new" hexagonal head cover (or the old interim slotted one with an annular ring cut into the head of the cover).

Flat6pac · 08-31-2009, 05:24 PM

The check for the oil pump from a German Porsche mechanic 30 years ago was..submerge the pump in oil, thumb over the pressure exit hole and you shouldnt be able to turn the shaft CCW after it loads with oil.
Bruce

Sigurd · 09-01-2009, 01:18 AM

Gentlemen,

thank you for your inputs.

As far as I was able see the block have the oil modification done. Most likely it was done during production since the block was made in '79. Changing springs forth and back was done to see what difference it would make. I am using the long (85 mm) spring with the guide and the 17 mm hex plug.

The procedure with turning the pump in oil by hand seems like an easy thing to do. Since there is no official way to check pumps I guess they generally are fool proof.

I think I will get hold of a four rib pump and change it to be on the safe side.

Long Norwegian winters have a benefit; it is a perfect time to work on the car.

304065 · 09-01-2009, 05:42 AM

Sigurd, you don't say which piston you are using-- a 1979 case comes with the oil pump modification already performed.

Now-- be absolutely certain you have things correct-- the oil PRESSURE spring is the LONG spring with the GUIDE-- it is installed VERTICALLY in the RIGHT case half. The oil OVERPRESSURE spring is the SHORT spring, it is installed HORIZONTALLY in the LEFT case without a guide.

There are two kinds of pistons, the one with holes and the one without. You want to use the one WITHOUT holes for a case that includes the oil bypass mod. If you use the wrong ones, the engine will not build oil pressure.

I would make certian you have the right parts in the right orientation before tearing down for this.

The oil pump is a positive displacement geared pump, it consists of the two rotors on shafts inside the housing. The housing is held together with four M6 studs and four M6 hex nuts. You can remove the nuts and carefully pull the housing apart to see the rotors.

Look for any damage caused by ingestion of foreign object debris. Also, look to see that the rotors are not digging into the housing. If there is excessive end play, you can sand the housing to reduce the clearance, but don't do it so much that the rotor doesn't move.

Sigurd · 09-01-2009, 10:47 AM

John,

the correct spring in the correct place is confirmed. (I checked in a hotel garage at the Nürburgring during the Oldtimer Grand Prix. Oil all over the place)

The pistons are the ones without holes.