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It's often said the oil pump is the heart of your engine. Its heartbeat pumps the oil which keeps your engine running. Considering it's such a crucial component, it's fairly easy to order the wrong oil pump based on looks alone.
Not only that but it's common for engine builders to swap camshafts and engine cases over the lifespan of your vehicle, further adding to the confusion of which oil pump is correct for your vehicle. We hope to cover the basic differences of air cooled oil pumps in this brief article, and give you some pointers so you can order the right oil pump for your vehicle.
Section 1: Engine Case & Oil Passage Ports.
Section 2: Flat Cam or Dished Cam.
Section 3: Drive Gear Sizes.
Section 4: Standard /Full Flow.
Section 5: Summary.
Engine Case & Oil Passage Ports
The diameter of the oil pump housings will be the same throughout all year Type 1 oil pumps. This means you can accidentally press the wrong oil pump in your engine case without knowing it was incorrect until you try to start the engine.
It's a simple mistake, and always a frustrating experience. Always confirm the oil pump you need based on your engine specs, not based on vehicle year alone.
Different year engine cases will have different size oil passages, and therefore different size oil inlet/outlet ports where the engine case mates with the oil pump. 1961-69 Type 1's used a single relief engine case which had narrower internal oil passages, used a single oil pressure relief valve, and ran at a lower oil pressure.
1970-79 Type 1's used a dual relief engine case. These engine cases had wider internal oil passages, used dual oil pressure relief valves (one by the oil pump, and a second by the flywheel), ran a higher oil pressure, and moved more oil.
Late model oil pumps beefed up the length of their drive gears from 21mm to 26mm in order to deliver more oil through 1970-79 dual relief cases.
Another engine case variant to consider is oil pump stud mounting holes, which changed from 6mm (1961-67) to 8mm (1967-79).
ENGINE CASE YEARS
OIL PUMP MOUNTING HOLES
12mm inlet/10mm outlet *(single relief)
12.5mm inlet/10mm outlet *(single relief)
14mm inlet/12mm outlet *(dual relief)
Flat Cam or Dished Cam:
Another factor to look for when shopping for an oil pump is the length of the oil pump drive shaft.
A FLAT CAM oil pump drive shaft is about 4-5mm shorter than the DISH CAM oil pump drive shaft. You can determine the drive shaft length by measuring from the back face to the end of the drive shaft tab.
Flat Cam Oil Pumps
Dished Cam Oil Pumps
Flat Cam Oil Pumps measure 2 inches from the back of pump housing to the end of the drive tab. These are designed to be paired with the relatively flat drive gear & keyway found in pre 1971 Type 1's camshafts. Dished Cam Oil Pumps measure 2.25 inches from back of pump housing to the end of the drive tab. The extra drive shaft length is required to engage with the recessed keyway found on 1972-79 Type 1's camshafts.
This difference in length may seem negligible, but it can mean the difference between not engaging your oil pump, or breaking the drive tab once the oil pump has been mounted. Both scenarios will result in starving your engine of oil.
That being said, air cooled VW engines are some of the most commonly modified engines in the world. If you are not 100% sure what camshaft is in your engine we suggest you remove the oil pump and inspect the drive shaft keyway found on your camshaft.
Flat Cam Oil Pumps
Stock for 1971 & earlier Type 1's.
Camshaft can be identified by 3 Rivets.
Oil pump keyway is relatively flat on camshaft.
Oil pump uses shorter drive shaft to engage Cam.
All aftermarket oil pumps are flat cam design.
Dished Cam Oil Pumps
Stock for 1972-79 Type 1's.
Camshaft can be identified by 4 Rivets.
Oil pump keyway is dished/recessed on camshaft.
Oil pump uses longer drive shaft to engage Cam.
Drive Gear Lengths
Once you have determined whether you need a flat cam or dished cam oil pump the next factor you'll want to look for is the gear length which is expressed in millimeters.
A wider and longer gear will move more oil. However, too much oil pressure is just as bad as too little oil pressure. Too much oil pressure will cause seals to fail, and then not only do you not have oil,
but you don't have a seal when you put oil back in. This is why it's crucial to use the right length gear for your engine.
Check with your local mechanic if you're questioning what length gear to use, but as a general rule you can use the following information:
21mm is typically used with a 1200cc engine or similar application.
26mm is typically used with a 1600cc engine or similar application.
30mm is typically used for full flow applications.
While it's usually not a big concern, you should keep in mind that gears can come in different widths such as M6 (larger) or M8 (smaller). In other words a shallower and wider gear can move more oil than a slightly longer and narrower gear.
Standard Flow and Full Flow Applications
Some oil pump applications require what is known as a "Full FLow Oil Pump". These performance oil pumps push more oil, while doing so out the back of the oil pump housing through an adapter plate (sold separately).
Full Flow Oil Pumps allow you to use external oil coolers, oil filters, or both. Note that installing a full flow oil systems bypasses the engine case's oil return passage and will require tapping your engine case for a new oil return line.
Full Flow Oil Pumps can easily be identified since they only have a single port (inlet) on the pump housing. Stock pumps have both inlet and outlet ports on the oil pump housing.
Oil outlet port drilled into oil pump.
Uses OEM pump cover.
Circulates oil inside the engine case.
21mm(1200cc / 1500cc) or 26mm(1600cc) oil pump gears.
Oil outlet port omitted. *(Oil flows out the back cover port.)
Requires full flow oil pump cover.
Circulates oil to external oil filter and/or external oil cooler.
30mm+ oil pump gears.
It's not uncommon for our sales team to receive calls stating the oil pumps they received are incorrect. Most often this is the result of a customer picking a replacement oil pump based on vehicle year alone without fully understanding what's in their engine. Classic VW's often have a long lineage of previous owners, and what came stock from the factory may no longer be in the engine after 50 years.
Picking the right fuel pump for your vehicle is easy once you know what to look for. Save the headache or installing the wrong oil pump, and mailing back a return by familiarizing yourself with the oil pump basics.