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I was looking for posts on how to inspect an oil pump to see if it needed to be rebuilt. Didn't find much. So the master, Gordon Raymond, and I swapped some emails on the topic. And as a result, decided (with Gordon's permission and guidance) to create this thread what will hopefully be a useful guide on how to assess the condition of a 2L stock oil pump, as well as the differences and applications of different types of OEM fuel pumps.

So here goes...

This thread is broken into the following sections:
  1. How to assess condition of a stock 2L pump
  2. Types of pumps & their characteristics
  3. What a “performance” pump involves
  4. What is the “best” oil to maintain pump condition?
1. How to assess condition of a pump

What the Pump Should Feel Like When Rotating the Shaft

A used pump should be rotate completely (100%) free, same torque all the way around. Any bind is caused by incorrect gear index involving tooth-contact, by either incorrect set up or debris. Both the idler pin stud and main shaft must be adjusted to parallel in both the X and Y axis. Unfortunately, this becomes progressively more difficult in performance built pumps with tight clearances. Further, most (all?) DIY pump builders lack the experience to do the set-up correctly.

Gear Clearances & Wear
There are some basic gear clearances outlined in Alfa documentation. It is attached with pictures. Essentially, check the following:
  • Internal oil pump gear end float in spec
  • Internal oil pump gear teeth clearance to body of pump in spec
This, plus saying to inspect gears for chips and other excessive wear is about all Alfa and other manuals such as Braden have to say about the matter.

Here are examples of what gear wear can look like…

The steel drive gear is here excellent and undamaged.
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This, however, not good
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This crank driven bronze pump drive gear shows minimal to NO metal transfer pits. This is good.
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And further, you can test the trueness of the gear bore to make sure it did not wear at a tapered angle. Being checked here with a plug gauge.
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Discussion Starter #2
Gear Shaft
Many tall gear (e.g. Alfetta) used pumps will have both considerable surface wear to the main shaft tip, as seen below
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… the bushing this tip rides in, in the lower body will be worn oval. This ruins radial clearances, and the pump is history. Shortly, you see considerable gear damage as well.

Piston

Original relief valve pistons typically develop vertical erosion scoring which wears through the very thin surface hardening with use. Gordon replaces these with new ones he has specially made of a much better alloy. Here’s why... Factory pistons were flash-surface-hardened only. When the thin not-too hard surface wears through from erosion, it then wears progressively faster until enough debris collects in the grooves to cause the piston to bind, losing the systems ability to regulate pressure/volume. A very hard piston will cause softer cylinder bore wear.

What to check for: If the erosion lines cannot be felt with a fingernail, it can be polished with very fine emery cloth, but the wear area should then be repositioned 180 degrees from the port. You can see the oval wear area below.
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Piston Bore
Below is an acceptable amount of wear shown in the piston bore. The radial lines are actually not wear, but “cutter” marks. The idea is that these will hold some oil in the bore much like cross-hatching in a piston liner. Just be sure there is no deep scoring.
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Some pumps, depending on how they have been machined, might be completely smooth like this one. That’s OK, too.
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Relief piston seat in the bore should be 90 degrees. How to check? Not really possible without machinist tools. But you can use the tool below to remove just enough old surface metal to get to 90 degrees.
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Here’s what it looks like when done (shiny part at bottom):
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Relief Spring
This should measure about 49 mm. Over time they often shorten by about 3mm. This is a special calibrated spring, like a scale spring.
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Pump Body - Lower
Example of good condition…no major scoring.
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Here are issues to look for in a pump body – note the scoring below
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And the top of the gear rubbing here
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Reassembly After Inspection
There’s probably only so much a DIYer can do to ensure perfection on reassembly, but a couple of pointers from Gordon:

To set the gear index, leave the 4 slightly nuts loose so you can move the two parts of the body in relation to each other, but still have each part stay in place while you rotate the shaft. Keep adjusting the two parts of the body until turning the crank becomes most effortless and consistent full through whole rotation. At that point tighten the 4 nuts so that they keep the two parts of the body from moving at all. Then remove one nut at a time (so that the body doesn’t shift from the index position you just set), add a lock washer and some Loctite Blue, and tighten.
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Discussion Starter #5
2. Types of pumps & their characteristics
There were two basic 2L straight-cut-gear pumps supplied by Alfa over time. A short and tall gear version. The short gear was about 31mm tall, the tall gear about 36mm tall. Here they are:

Short bottom, tall top.
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The difference is one of application. The 31mm gear appeared in the Alfetta period and was intended for use with 20-50 mineral base oil.

The tall gear appeared much later when lighter weight oil was used for improved gas mileage. This pump is sometimes called the HD pump, but that does not refer to "Heavy-Duty", as using this pump with 20-50 mineral base causes terrific cold oil gear loading issues with resulting gear and pump failure. Many tall gear used pumps will have both considerable surface wear to the main shaft tip as noted previously.

If a 36mm tall gear pump is used, it should be used with the correct lightweight oil, or a synthetic. The short 31 mm gear straight cut pump is a better performance pump, but again, not designed for high speed use. Modifying a straight cut 31mm gear pump for race use is possible, but not as cost effective (use and failure from wear over time), as using a 9 tooth helical pump, originally designed for high speed engines.

There are issues in the base design of the straight cut pumps that do not exist in helical pumps. There are many reasons for this, but it is good enough to say that since Alfa already built a high speed pump, and the 2L pump does not easily present a platform to re-invent it as a high speed pump, just go with a helical variant.
 

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3. What a “performance” pump involves
Why customize a pump? Well, usually for high performance and race applications. Many considerations and variables go into designing for the application like: what type and grade oil do you wish to use? Does your car use a remote filter or oil cooler? Do you use a recuperator like “Acc Sump”?

Your core pump is a 2L straight cut gear pump, which was designed for use in LOW speed 2L engines. When you build a performance engine that runs carburetors in place of fuel injection, it is normally run faster with different cams, pistons compression and ignition for serious power gains over its original configuration.

Where the FI engine was limited by the FI to 5500 rpm or so, the rebuild will now run faster, to 7,000 or so. An oil pump designed for low speed high volume, will have some problems when run faster than its intended design. We now need a high speed oil pump such as that used on the older engines that ran Webers. Over time, Alfa used many different oil pump designs for different engine applications, and we need to look to the earlier high speed pumps to as a core to become a high speed performance pump.

Racers like to use 1750 oil pump cores for race 2L oil pumps. These are now getting hard to find as they have been pretty much used up. At speed, straight cut gear pumps trap oil between gear teeth, and the teeth push apart. This causes idler pin tilt and a bow in the main shaft.

When building a performance pump, all pumps start out with the same plan. Eliminate factory manufacturing tolerances. Gordon starts with the main shaft, checking for straight in his lathe. If a 105 shaft is not true, it’s trashed, and a better shaft found. If a 101 shaft, and shows a bow, that is straightened.

Components
Gears: a double index, GTA hardened race gear set.
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Custom oil pickup
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Hardened main shaft – this one for a 105 identified by the wide fuel pump cam at the shaft top.
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Custom gear prep & machining
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Hardened idler pins – High performance idler pins are custom ground. They are hardened all the way through, very hard. They are slightly oversize in diameter. Factory surface hardened only pins are .474”, mine are .0005+ oversize.
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The pin is a closer fit to the gear bore, allowing a tighter radial clearance set up in the pump bottom, but more important, as the gear turns, oil trapped between the teeth is forced, under pressure, to float the gear bore on an oil film, and at the same time, this oil flow washes away debris in the oil that otherwise collected at the base of the idler pin. This debris is what wore the gear bores tapered and wore through the surface hardening on factory pins. Now the bronze idler gear lasts as long as a steel idler, while providing more oil volume from tighter clearances. This oil pump inside an oil pump works VERY well.
 

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Discussion Starter #7
4. What is the “best” oil to maintain pump condition?
Overall, oil pump life depends on using the correct pump for the application, with the correct oil, changed at reasonable intervals.

This is not meant to start oil jihad. But…

There are 2 popular 20-50 mineral base race oils used with Alfas made by Valvoline. Gordon uses 20-50 VR-1 in his GTA and single plug 1600 race engines as this oil has a dispersant, rather than a detergent to resist foaming. Debris in the oil remains in suspension if the oil is circulating, but gradually settles out (about 28 days) left sitting. This race oil is changed by noting opaqueness of a drop on the dipstick, hot. If you cannot see through the drop, it’s time for a change, or if the engine will sit, non-running, longer than 2 weeks, the oil is changed hot before lay up. The VR1 and the other semi-synthetic Valvoline 20-50 race oil (BLACK container) both have plenty of ZDDP zinc additive for flat tappet (Alfa) engines. Gordon prefers the VR-1 version and have used it in race Alfa and Ferrari engines since 1972 with NO oiling related failures. Cheap enough to change often!

All that said, Mobile 1, 20-50 or 20-40 if you cannot find 20-50, is the ONLY full synthetic that behaves like a mineral base, thinning as it heats. This is because, as originally designed, it was supposed to be mixable with mineral base in mineral base designed engines.

Over the years, Gordon had one racer that used 20-50 Mobile 1 in his engine, and sent him the pump (his build) at engine rebuild time for a check up. It showed NO wear, and no oxidized oil film anywhere, typical of synthetic race oil in my synthetic pumps. However his pump was built to use 20-50 mineral base. Gordon was impressed with that.
 

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Makes me wonder how my stock 1985 pump has survived running up to 7000 rpm on Rotella T 15W40 for all of these years.
 

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Richard Jemison
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Yep! More work than really justified, particularly for different oils. A gear pump will generally live an extremely long life if it`s pumping oil and not solid matter.
 

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A gear pump will generally live an extremely long life if it`s pumping oil and not solid matter.
When I worked for a living I did some engineering on high pressure turbine filters that used gear pumps for seal lubrication and they ran 24/7 for year after year without problems. They were the close to bullet proof.
 
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