Date: Sat, 30 Nov 1996 11:44:21 -0800
From: Mike West <mwest%CDSNET.NET@VM1.CC.NPS.NAVY.MIL>
Subject: Oil pump, a heart for the tin man

Our own heart has many features that most of us are aware of.

 It carries food and lubrication to the various parts of our
body and picks up the poisons and residue from work on the way back
and sends it thru our kidneys for cleaning, then back to the first
chore.

 Additional chores are to spread the warmth and cool the parts if
too warm.

 It's a gear pump. One of the simpest and most reliable made by man.
Past, present or future.
 First cousin to the Noble Screw it has all of his features of loyalty
and sturdiness.
 Put it in and forget about it.

 This gear pump is the same design I used to use in Hydraulic Forklifts

 It will even pump Aspahalt and does in those machines that lay the
stuff. You can pump air with the damn thing just not too well.

 It will of course also pump water. They just put in some brass gears
and ship it. Can't think of the manufacturer right now.

 We're talking about the same pump for all three aplications.

 Here's the way it works: there are two gears and one is driven from
outside. In our case it's driven from the end of the camshaft.

 The two gears mesh and each has its own circular pocket in the
housing they're in.

 There's a cavity on one side of the gear teeth to less then half the gear
diameter of the gear.

 This closes down around the gear to just a nats eye-lash where it
 reaches the center of the gear.

 There's another cavity on the other side for oil to be pushed out of the pump.

 The area in the center of the pump, where the two gears mesh is all
closed in and tight.

The sides of the gear, where the teeth ain't, are also within a nats
thing so the fluid can't escape down the sides.

 One gear is exposed to the incoming fluid and it picks it up with
its teeth and then the fluid gets trapped there when the wall of
the housing closes down and it is transfered to the other gear where
it is rotating into the housing and is moved into the high pressure
side of the pump.

 The high pressure or low pressure side only depends on which way
you turn it. Works just as well in reverse.

 The only important thing to this pump working is the clearance
between the teeth and the walls and the walls on the sides of the
gears.

 The teeth in our small pump are steel same as the ones in my
hydraulic system.

 The hydraulic system had a heavy cast iron housing and generated
pressures of 5000 psi. All day long and sometimes 24 a day.

 The only difference is that housing. Ours is made of aluminum.

 That little pump would probably still go to a thousand psi before
it blew a wall out.

 It be bad!  :-)

 You wouldn't bother the camshaft to do that and probably not the
gears that drive the cam.
 You may stall the engine tho.

 The weak points are the aluminum walls and the clearance between
the walls and the gear.

 Flow rate: this is based on the size of the teeth and the rpm.
A tooth can only hold so much fluid so that's pretty easy to see.

 From Tom Wilsons book, "How to rebuid a volkswagen engine" it shows
seven different lengths of gears for those pumps.

 These different lengths equate to different flow rates for the
different engines.

 For the type 1 there are four pumps according to Tom Wilson.

 The differences:

 Case oil passages thru '69 were 8mm. Starting in '70 the oil
passages were opened to 10mm and the second oil relief valve was
added.

 VW oil pumps and camshafts are matched parts!
As I recall the difference here was the flat cam gear and the
dished cam gear. Make sure you get the right one at rebuild.

 Oil pumps are named for the length of those gears. Cool!!

 The 40 hp thru '67 engines used a 17mm pump

 From 68 thru 69 the pump was 19mm.

 For '70 only thru August, a 24m pump was used.

 From August,'70 (71 model), a 26mm was introduced

 The 17 and 19mm pump go with the flat gear cam and can be inter-
changed. Naturally the 19 has a 10 percent higher capacity so
that would be my choice.

 On the other hand, to the best of my knowledge, you could use a
later camshaft and go all the way up to the 26 mm pump.

That is not a good idea unless you work out some way to open the
oil passages in the earlier case.

 You'd have too much flow which would just become too much
pressure. Drag your horsepower down etc.

 More to the point the earlier cases with the small oil passages
and pick-up tube would starve a bigger pump for oil.

 Or blow it up because the oil couldn't get out the small outlet
in the case fast enough.

 The 24m pump uses a 3 rivet dished gear and the 26mm pump uses
a 4 rivet dished gear.

 Probably can use the 3 rivet for a 26mm pump but they put the
extra rivet in there to drive the bigger pump.
 Could shear the gear off in extremes.

 Type 1-3 and type 4 pumps are inter-changeable per T. Wilson.

 The Bentley gives me 28psi operating press. using 30wt oil at 158F (70C) @
2500 rpm,
 The oil light comes on at 2-6 psi.

 Unfortunately it doesn't say which pump or what the flow rates are.

 This little pump drags the hell out of your engine in the morning
when the oil is cold. The main reason your idle is so low at that time.

 So we covered that pretty good let's get into a couple other
aspects that need addressed.

 The fit of the pump case to the housing: The only seal around the
inlet or outlet is the pressure from the case itself.

 If that pump doesn't fit hard the oil just runs out and back into the
sump. The same on the inlet, you'll just be sucking air.

 Bob Hoover has a "Sermon" on this so check it out.

 Next is the sharp corners in the pump and the case passage which
create some extreme pressure drops. Radius or chamfer them.

 Those gear/case clearances: it's in the book but I'll read it to
you. Backlash: the slop between the gear tooth faces, .008" or less

The end-play or side clearance: should be less than .004 without a
gasket. I want .001" or less in there.

 The book shows no check on the clearance between the tooth end and
the case. That's crap, I want the same .001"-.004 in there.

 Do not put a gasket on the cover plate where it mates with the
gears if you don't have a good face, use a little permatex.

 Frankly if you don't have a good face how you going to get the
.001" I told you to have?

 Between the case and the pump flange put what ever you want as
thick as you want. Say a 1/16 gasket.

 The ruling factor on the above is where the holes in the pump
line up with the holes in the case and the shaft end fitting into
the cam gear. Adjust accordingly.

 You do this right and you will be justly rewarded.

 You do it wrong and you will still be justly rewarded, you just
won't like it.

 This is the heart that pumps the lifeblood of your engine and it needs to
be treated as such. "Serious as a heart attack" is not just
a figure of speech.

 Now for the commercial: clear back at the beginning I spoke of
how your blood carried away the poisons and crap and sent it thru
your kidneys.

 Our little stock engine has no kidneys.

 We are expected to just dump it's blood out and put in new.

 It doesn't quite work that way.

 I don't care if you changed oil ten minutes ago, you do not have
clean oil.

 On a big monster machine, I burnt up $12000 worth of hydraulic
pumps and motors finding that out. It even had super bitchin'
filters. They just wern't fine enough.

 President of the company running around yelling "flush the system,
 flush the system!" He didn't even know what that meant.

 So we need a kidney, guys, an oil filter. Full flow oil filter.

 If you look around, they make one that is a pump/filter combo
these days and it's an easy fix.

 The other way, where you drill and tap the case and pipe it in is
better in my opinion but get something in there.

 The bearings, being a lot softer than the pump parts are going to
be the first to go.

 No disclaimers, Fram can send me money for every filter they sell
if they want. :-)

 west



















Oil pump, a heart for the tin man