Oil Pump Specs / Inspection

911inSC · 12-29-2009, 05:18 PM

I am in the middle of an engine rebuild on an '81 911 SC initially brought about (like I am sure many are

) by a broken cylinder head stud. Anyway, I'm about to start going back together with the engine, but I want to make sure the oil pump is in top condition before I plant it back in the case where it will take another teardown to access. In most cases I woul just replace the pump during an engine rebuild, but seeing how this one cost around $800 and I don't have any reason to believe it is bad, I am opting for a good inspection instead.

I am in the precision tooling and machine shop business, so I have the capability to precisely measure the internal clearances of the pump. However, I have been so far unsuccessful in finding any information on these internal clearances.

I have refurbished several hydraulic gear pumps (industrial) before and typically the most wear is seen between the faces of the gears and the housing. I would particularly like to know what the specs are for these end clearances in the oil pump.

If any one has this information or knows where to find it, I would be very grateful for the information.

Thanks.

Flat6pac · 12-29-2009, 05:31 PM

You didnt have a pressure before disassembly?
Bruce

911inSC · 12-29-2009, 05:36 PM

I did have decent oil pressure before disassembly. I'm not looking for pressure specs. I am looking for internal mechanical clearance specs for the pump. I just want to make sure it has plenty of life left before I seal it up in the engine case where it is very hard to get to. I'd like to "blueprint" the pump, and put it back to new condition before I re-assemble the engine.

Eagledriver · 12-29-2009, 07:20 PM

I've built a couple of engines but am not an expert on the oil pumps. The 911 oil pumps seem to be very robust. I just do a visual inspection of the gears and housing. Some people do use new oil pumps on rebuilds but it seems to be the case that for most of us, if we had good pressure before we disassembled the engine we just re-use the pump and have no problems. Sorry I can't be of more help.

-Andy

304065 · 12-30-2009, 04:28 AM

Quote:

Originally Posted by 911inSC

I did have decent oil pressure before disassembly. I'm not looking for pressure specs. I am looking for internal mechanical clearance specs for the pump. I just want to make sure it has plenty of life left before I seal it up in the engine case where it is very hard to get to. I'd like to "blueprint" the pump, and put it back to new condition before I re-assemble the engine.

As far as I know it's never been posted as a specific value. You can search here for threads where people put the housing on a piece of sandpaper on a surface plate and take material off to reduce the clearance between the gears and the housing-- a Grady Clay post about using machininst bluing to verify that zero-clearance had NOT been achieved comes to mind.

Good luck!

matt demaria · 12-30-2009, 06:58 AM

Gear backlash is .03 to .08mm. End play is .035 to .1 new . .2mm is the werar limit.

Walt Fricke · 12-30-2009, 10:16 AM

Matt - where did you find those specs? First I have seen mentioned. I'll be embarassed if it was from the standard shop manual.

End play seems to be the only thing you can do anything about as a practical matter. Somewhere I recall reading of someone who installed bushings in the shaft holes.

But Andy is in the clear majority - if the engine did not blow up, the pump usually gets cleaned and visually inspected through its openings to see if there are gouges on the tops of the teeth, and reinstalled if all looks OK.

Walt

911inSC · 12-30-2009, 04:18 PM

Matt,

Thanks. That's the kind of info I have been looking for. I would also be curious to know where you found it.

I appreciate everyone elses thoughts as well.

On the industrial hydraulic pumps we have repaired, we usually just end up machining or surface grinding the housing flanges to put end play or axial play between the face of the gear and the housing back in spec. I was thinking of taking a similar approach with the oil pump.

BURN-BROS · 01-01-2010, 09:54 AM

The biggest issue with oil pumps is the area between the drive shaft and the scavange gears. The shaft will experience some galling, preventing the gears from sliding axially along the shaft. This then causes wear between housing and the end/face of the gear.