Sportster Oil Pressure and Dynamics

[Hippysmack]

It's cool.
If nobody wins a conversation, it was a good conversation.

[Hippysmack]

Lubrication Regimes

Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces.
The study of lubrication is a discipline in the field of tribology.
Lubrication mechanisms such as fluid-lubricated systems are designed so that the applied load is partially or completely carried by hydrodynamic or hydrostatic pressure, which reduces solid body interactions (and consequently friction and wear). Depending on the degree of surface separation, different lubrication regimes can be distinguished.

Lubrication regimes describe the type of lubrication film that is created under specific operating conditions and is dependent on the degree of contact between surfaces.
There are four lubrication regimes: Boundary Lubrication, Mixed Lubrication, Hydrodynamic Lubrication and Elastohydrodynamic Lubrication.

The drawing below describes how a journal bearing operates to establish the oil film it rides on (as in between a cam journal and it's corresponding bushing).
At startup, the journal is generally sitting directly on the bushing with residual wear agents from the oil between the journal and bushing or sitting on a very light film of oil at best.
As the cam begins to rotate, oil is rotated under the journal and forms a wedge lifting the journal as it rocks in the bushing ID.



And lifter to camshaft oiling.


Boundary Lubrication
During boundary lubrication, opposing surfaces meet with little or no oil film separation. In this regime, damage is prevented by protective additives that promote sliding rather than welding of surface asperities. Friction may be at it's highest level during the boundary lubrication regime. This occurs at start-up, shutdown, low speed or high load conditions. Boundary lubrication regimes occur during any condition where the asperities of two lubricated surfaces in relative motion may come into physical contact and the potential for abrasion and/or adhesion occurs. It has been suggested by lubrication engineers and tribologists that as much as 70% of wear occurs during the start-up and shutdown phases of machinery. Wear additives in the oil play a huge role.

Mixed Lubrication
Mixed lubrication occurs during the transition from low to high speed operation when boundary and hydrodynamic conditions coincide, the asperities of bounding surfaces will extend through the film and occasionally come in contact. Generally speaking, boundary lubrication is dramatically reduced as sliding speed increases, creating a wedge of lubricant film between the surfaces in motion and some friction is reduced. Some metal-to-metal asperity loading is still occurring combined with loading (lift) on the lubricant. Wear additives in the oil play a lesser role as the oil film is introduced under the journal. This is an intermediary condition between boundary and hydrodynamic/elastohydrodynamic lubrication regimes, the gray area between them. As the oil film thickness increases further, the system now moves into full film lubrication, either elastohydrodynamic or hydrodynamic lubrication.

Hydrodynamic Lubrication
Hydrodynamic lubrication occurs when the lubrication film between the two contact surfaces (as in journal bearings) is thick enough that the two contact surfaces are completely separated by a viscous oil film. At this time, the frictional force between two contact surfaces is determined by the viscous resistance of the lubricant, resulting in a very small value (coefficients of friction can be 0.0001-0.01). Under this condition, when the shaft is rotated, the oil around the shaft also rotates due to the viscosity of the lubricant oil, generating oil pressure at the load area. This phenomenon is called the wedge effect. The oil pressure generated within the lubricating oil film is affected by changes in temperature and viscosity of the lubricating oil, surface roughness, and clearance and rotational speed of the shaft. When the journal rotates, it creates an oil taper or wedge between the two surfaces, and the pressure builds up within the oil film supporting the load. Wear additives play a limited role at this point. Although full-film lubrication does not generally allow metal-to-metal contact, abrasive wear or scratching can still occur if dirt particles penetrate the lubricating film.

In hydrodynamic lubrication, the lube oil film thickness is greater at the inlet than the outlet pressure.
Inlet pressure increases quickly, remains fairly steady having a maximum value just pass the bearing center line, then decreases quickly to zero at the outlet.

Elastohydrodynamic Lubrication
Elastohydrodynamic lubrication conditions occur when a rolling motion exists between the moving elements, and the contact zone has a low degree of conformity. For example, the curve of the roller and the race in a rolling element bearing are very dissimilar. In fact, the roller and inner race are curved in opposite directions and thus have a small contact area (almost a single point of contact). This creates high-contact pressures. As the oil enters the contact zone between a ball and raceway (by rolling action), the oil’s pressure rises sharply. This high pressure in turn significantly increases the oil’s viscosity and load-holding ability. This concentrated load will slightly deform (flatten) the metal of the rolling elements and race in the contact zone. The deformation only occurs in the contact zone, and the metal elastically returns to its normal form as the rotation continues. Obviously, the metallurgy and heat treatment of the metal are very important to this lubrication regime. Because an oil’s viscosity is directly affected by temperature, it is also clear that incorrect or abnormal operating temperatures will interfere with the formation of the elastohydrodynamic lubricating (EHL) film.

Examples of machinery applications that operate under EHL are rolling element bearings, gear teeth and cam contacts (rolling) where high rolling contact loads occur. If operating conditions such as speeds, loads and temperatures are not exceeded, asperity contact may never occur due to this remarkable characteristic of lubricant and metal. This is similar to a roller lifter on the Sportster camshaft as well. The oil film thicknesses are often are very, very thin. However, EHL is considered to operate on a full fluid (oil) film.

[bustert]

hummmmm
here we go again
yes the seals will work on the ole spur pumps. there was a BIG discussion with oldschool over this. you can do the work with common shop tools and 35 dollars in the pocket, not 100+ on his modified plates. can be done with an off the shelf parts.
hd was and is all about the $$$$$$
in the past, they never threw away anything so you saw parts over model years, my 74 is more 73 and back.
it is easy to make a test plug for the check, 98% do not leak and most go about it the wrong way to fix it. also, there were mfg process changes between the years so the angle of the dangle is diff. all of this is already on the forum so no need to waste server space here.
i admire the efforts of mr. hippy but all of this is moot since he cannot say with proof what he actually has.
all of the mumbo jumbo is really a distraction and basically is a waste of server space.
the three things i mentioned he never really addressed, shear speculation.
like vectoring in the color on an old analog tv, millions of possibilities and to boot, everyone sees color differently, shoot most cannot till 720 from 1080 pixel.
controlled leak, i doubt, saving $$$$ on a machining process probably.