Oil pump clearances

[ajwans]

Would anybody share with us what the internal clearances for the
oil pump should be?

andy

[Walt Fricke]

Do a search. Use Grady Clay as one of the seach terms. I think there are end clearances (which you might be able to reduce by machining if too large). Not sure about side (which couldn't be changed anyway). But I don't think you need to worry about side clearance as nothing rubs. If junk went through the pump you can look for scoring.

[ajwans]

Here is the inside of the pickup end (click on image for higher res version):



As you will see there's a radial score near the end where it looks like the
pump ingested a single piece of rubbish. Otherwise clean.

I searched and found only one post which listed the end play wear limit at
.2 mm, does this sound reasonable? Link (Oil Pump Specs / Inspection).

andy

[ajwans]

Here's the pressure end of the pump:


2010-12-01 11.08.05, on Flickr

Would anyone like to comment on the circles shown in red, I am
thinking this is where the rotating gears have gouged material and
that the pressure end ought to be milled or sanded to bring the
dimensions back to stock, I have not yet measured the depth of these
gouges but I will.


1291163237392_29ec2, on Flickr

andy

[ajwans]

The depth of the housing is approximately 0.2mm (0.008") deeper
than the length of the pump gears. Is this too much space around
the ends of the gears to get optimum pressure?

andy

[Grady Clay]

Andy,

Thanks for the ‘heads up’.

From what I can see in your images, the pump housing looks relatively undamaged.
I suspect the gears are in similar reasonable condition.
Try and improve the focus on your Flickr images.
It is difficult to inspect these parts with internet images.


Gear pumps are remarkably tolerant to abuse from debris.
They also don’t lend to re-machining.
If in doubt, replace it with new.
The good news is there have been continuous improvements in the capacity of the pumps.
Be sure to investigate the scavenge-to-pressure capacity ratio.

It used to be that a new pump was ‘perfect’ and simply installed.
No longer.
Every pump should be disassembled, inspected and measured.

There is the end clearance measurement.
There is the condition of the inside of the machined casting.
There is the condition of the ends of the gear teeth where they clear the casting.
There is the redial clearance between the gear teeth ends and the machined casting.
There are the condition of the teeth faces where they contact and transfer during rotation.

The keys and key-ways should be inspected.
The drive shaft must be undamaged and ‘float’ free.
This is a powerful pump.
The highest load on the pump is on cold start-up with sudden high revs.

Keep in mind a few facts: The full oil pressure seals across the gear-pair contact line.
The oil is carried in the spaces between gear teeth around the perimeter on both sides of the pump.
The oil pressure is divided among the gear teeth around the perimeter where the teeth are adjacent to the machined casting.
There is full oil pressure across the ends of the teeth that are contacting.
The pressure pump (should) see only (100%) oil with no entrained air.
The scavenge pump sees 100% cold oil on start-up and about 40% entrained air during normal operation.

The pump’s condition is most important when the engine is not running full oil pressure (hot and idle to before the rpm gets to the regulated pressure).
A measure of this is the rpm where full (regulated) pressure is achieved with a given oil temperature (and lots of other factors).
This is important as the piston squirters only open above a particular pressure (42-56 psi for 911) just less than the regulated pressure.



My classic example was a new GT3Cup pump (from Porsche Motorsports) where the scavenge casting was incorrect.
There was about 30% of one side where there was no metal to have been machined.
This left a huge gap preventing proper scavenging of the engine at high revs.

I hope this helps.

Best,
Grady

[ajwans]

Originally Posted by Grady Clay

Andy,

There is the end clearance measurement.
There is the condition of the inside of the machined casting.
There is the condition of the ends of the gear teeth where they clear the casting.
There is the redial clearance between the gear teeth ends and the machined casting.
There are the condition of the teeth faces where they contact and transfer during rotation.

Thanks Grady, I will attempt to create better images, I have a very nice compact,
Canon S90 which I'm sure is capable, it is I who is deficient in the photography
department.

What do you consider the end clearance should be? I am trying to get this pump
as close to perfect as possible, it will save me splitting the case open again.

andy

[ajwans]

I have been practising my photography and generated these better
images. Click through for higher res images.



IMG_3942, on Flickr


IMG_3941, on Flickr


IMG_3933, on Flickr


IMG_3932, on Flickr


IMG_3931, on Flickr


IMG_3930, on Flickr

andy