Carrera Oil Pump upgrade

[AndrewSlater]

I have just purchased a used 3.2 Carrera 4 rib oil pump, with a view to upgrading the oil pump in my 2.7l engine when I get around to the rebuild.

I wanted to check the condition was OK as I spotted some small lines in the teeth of the gears when I rotated it so I have taken it apart.

There is a very minor nick on two of the gears as shown in the photo below.



and here is the inside of the chamber.



The other chamber is spotless as are the longer gears.

The wear on two of the smaller gears looks very minor to me but then I'm not an expert.

Can anyone tell me whether I should be worried about the minor scoring?

As always any advice much appreciated.
Thanks
Andrew

[AndrewSlater]

Anyone - or do I need to take some better photos?
The part is a 3.2 Carrera 1984-89 part number 91110700805 if that helps.

As an aside where would I get a replacement gear if I needed one?

Thanks Andrew

[haasad]

Andrew, I think fetuhoe wrote some stuff on oil pump checking here or on Pelican. If you do decide to use the one photographed its best, if not considered critical, its re-assembled with all the parts in exactly the same orientation as originally. It must turn freely and smoothly with no tight spots.

[AndrewSlater]

Thanks Andrew, I did carefully mark all the gears so I know how they all meshed together ready for reassembly.

I did try a search for a useful thread but not found one yet that has informed me one way or the other.
There is one on Pelican that talks about backlash specs etc but can't find many photos of acceptable wear and tear ( if any ).

I was also interested to see if you could swap the position of the top and bottom gear pairs so that the minor nick in the gears no longer lined up with the position of the minor score on the bore.

I will check the condition of the one in my engine for comparison purposes when I get that far.

I will continue the search for more info.

[AndrewSlater]

Further...

I probably should have said that the minor scoring is at the scavenge side of the pump.

There is no sign of any wear on the pressure pump side as below:-



I've read that it is the pressure pump side that is more critical - can anyone confirm this?
Thanks again

[fetuhoe]

Gear pumps are quite simple devices but can be affected by any wear in the housings.

The pressure side will be most affected as the amount of 'spill' will be influenced by both radial and axial clearance.

Spill, which is the leakage from the pressure to the suction side of the pumps is clearly affected by the pressure difference in a linear manner and is the square of the axial clearance.

It is rare that there much spill through the gear mesh but marking on the teeth or radial scoring can be an issue if it is severe.

It is difficult to assess the level of influence of any scoring on flow but as long as the engine develops the correct oil pressure it won't be a problem.

As Andy says it is very important to assemble the pump with the same teeth in engagement otherwise they can wear very quickly and shed small metal particles.

I am not sure it is fair to say that the scavenge section of the pump is less important as the level of pressure in a 911 crankcase has a significant impact on windage.

If the case is full of a heavy oil vapour then the parasitic losses can be quite high and this will also have the effect of making the oil temperature higher as the power loss will be seen as 'heat to oil'.

The best 911 pumps have a significant amount of scavenge capability and in fact is a vacuum pressure can be achieved in the case it would be the best result.

It is likely, however, that the scavenge section is less affected by wear as the DeltaP is always low so spill will be negligible.

I imagine you will carry out the case By-Pass modification and change the pressure relief valve piston for the later (Post 1976) type.

[AndrewSlater]

Thanks for the advice - sounds like everything should be fine.

If I use the pump I do intend to make the By-Pass modification and change the pressure relief valve piston accordingly.
I've yet to investigate the engine thoroughly yet, but having bought the Carrera Oil Pump I was eager to check its condition.