Oil Pump Blueprinting

Oil Pump Blueprinting

By Martin Gonzales and Mike Kojima

What is as important to your engine's health as your heart is to your own body?  If you guessed the oil pump then you are absolutely correct!  Like your heart, your oil pump circulates the engine's life blood, oil, around to critical components like your engine's bearings and valvetrain.  These parts, like parts of your own body, would only last seconds without a continual supply of pressurized oil.

Many people don't take care of their heart; they eat fatty foods, smoke and don't exercise. A lot of the time, this results in a heart attack and an early demise.  Likewise the oil pump is a part that most people don't regard in an engine build.  If it fails it can just about be guaranteed that your engine will suffer serious damage in one form or another.

Bearings are made of super soft metal to ensure that they have good embedabilty.  The soft metal absorbs particles of dirt so they have less chance of damaging the crank's harder journals.  The soft bearings are less likely to damage the hard crank journals if they happen to touch as well due to oil film failure.  Here is a dirt contaminated bearing.  Because the metal is so soft, oil pressure must always be maintained under operation and if oil pressure is lost, the soft bearing will be chewed up by the crank in a matter of seconds.

An engine's main and rod bearings are made of a soft material.  This is to ensure embedabilty, the bearing's ability to suck up dirt and debris so it won't damage the crank journals.  In the old days, bearings were made of lead.  Now they are made of zinc/tin alloys with copper, antimony and indium added for some additional strength and hardness.  So you can imagine how easy it is to damage the bearing.  In fact you can dig your fingernail in to many bearings.

If oil pressure is lost, the soft bearing material gets chewed up rapidly, then the steel shell microwelds itself to the crank, sticks and spins.  This usually results in total destruction of the engine.

Once the soft metal is breached, the crank journals will begin to score.  Light scoring can be machined out by grinding the crank undersized and using an oversized bearing.  Much more than this and the crank is thrashed.

Bearings depend on a hydrodynamic pressurized film of oil between the bearing surface and the crank journal to work; if this goes away the rapidly spinning crank journal makes quick work of the soft metal bearing.  The bearing will usually be damaged in seconds under load if the engine loses oil pressure.

A Hydrodynamic film is created by a Spinning journal within a bearing fed with pressurized oil.  There is no metal to metal contact while the oil pump is operational.

Not many people consider the oil pump in a build, perhaps because it's not a sexy power increasing part or perhaps because it's not talked about much.  It is however perhaps the most critical part for an engine.  It is also a highly stressed part which can be prone to failure.  Most engines uses what is called a Gerotor pump. A Gerotor is a positive displacement pumping unit. The name gerotor is derived from "Generated Rotor". A gerotor unit consists of an inner and outer rotor spinning inside a sealed housing. The outer rotor generally has one more tooth than the inner rotor. The inner rotor is located off-center inside the outer rotor and both rotors rotate. During part of this assembly's rotation cycle, the area between the inner and outer rotor increases, creating a vacuum. This vacuum creates suction, and hence, this part of the cycle is where the intake port is located in the housing. Then, the area between the rotors decreases, causing compression. The exhaust or exit port is located over this area in the housing. Gerotor pumps are generally designed using a trochoidal inner rotor and an outer rotor formed by a circle with intersecting circular arcs.

Gerotor pump showing inlet and outlet flow	A Gerotor pump has one less tooth on the inner gear than the outer gear has.