wondering about oil pump function

[worn]

An incident resulted in steel bits getting into the sump and thus the oil pump. Set that aside as I come off looking bad. My question is how the resulting scratches in the impellers and the case affect function. Don't tell me to replace the pump - I already know that. I have two questions:

How much does scoring affect oil pump function? The scratches look really small relative to the size of the pump components. I would expect the scavenge pump would be affected most because air is much less viscous than oil. Is there any real data about this?

Second, do scratches propagate increased wear on the pump itself? I recognize that reduced oil pressure will increase engine wear, but beyond that and increased windage and crankcase heat is there damage to the pump itself.

Thanks, and yes I have a wtb for a replacement.

[r lane]

Send pictures and is it a street or track. The only way to know the level of damage is to be able to bench test it against a new one. It is not just the gears but bore as well. If you have gouges, that is a problem, but small scratches that you can barely feel with your finger nail, I am not going to worry.

[worn]

Thanks. I am curious if there is a setup for bench testing these pumps aside from the Porsche engineers. If so, I would love to hear more.

[r lane]

To replicate all conditions in a test rig could get involved. To do a basic test stand would be to build an oil plumbing system as in your car, find a way to spjn the pump at appropriate rpms. Not sure it is worth the effort as pumps have a low failure rate, at least from my experience.

[worn]

When an oil pump fails, what happens to the pump? I am pretty sure I can imagine the down stream effects of low oil pressure, but what changes at the pump as it fails? Thanks.

[iamchappy]

ive had bad luck with oil pumps, have had two fail, the last was a 930 pump with less than 4,000 miles on it, no debris found in pump. Both pumps seized and snapped intermediate shaft. The later failure had the chain rattle sound before it failed.

[stownsen914]

Sounds like iamchappy has had bad luck with oil pumps. Not sure that's a common failure mode. Many fail due to debris running through them and scoring the housing and/or gears due to a failure elsewhere in the engine. Some become corroded due to sitting for long periods. I've understood that some show effects of long term use like increased clearances, etc. 964 pumps have a reputation for cracking the magnesium housings. I haven't heard of that issue with the earlier mag ones.

[dannobee]

One thing that many people fail to do is to center up the oil pump before you tighten down the nuts. The intermediate shaft "dumbbell" should easily move fore and aft in the case with the oil pump nuts torqued to spec. If it doesn't move freely on the shafts, back off the nuts and try again until it does.

As far as the scoring, post some pics and have us take a peek.

[iamchappy]

Dumbbell as in the splined shaft that connects both, I will certainly check that when i start to assemble it.