Is it a combination of.

1. bearing clearences

2. intended useage ex. drag,circle track,roadcross etc...

3. Power levels ex. in my opinion a 1000+ hp motor would need better protection than say a 500hp motor.

4. Ambient temperature ex. Arizona is almost always triple digits, and michigan is 80's or less

Those are just some of the possible examples for chosing the correct oil. Because most of us here have some type of power adder so i dont believe going with what the owners manual says will be adequate for our applications because i dont belive that all oils are created the same.

 

I'd prob say 1 & 4 are the biggest concerns.

 

Agreed.

 

So what weight for what criteria?

 

Loose bearing clearances - purpose built race motor - require a thicker oil so some press can generated. Cold weather temps - stock motor - require a lighter/thinner oil for cold start up.

 

I am going to be running diesel oil cause I learned it still has zinc. Is 15w40 a good spring to fall (non-winter car) weight?

 

Sure. On the zinc, I thought most had been removed because of catalytic converters,even the diesel oil? Last I read, awhile ago, was that motorcycle oil still had a good amount of zinc because it also lubes the trans and they don't have cats.

 

From what I read it s called ZDDP or something like that. I will brush up on my reading to verify.

 

Viscosity: "Friction opposes the movement of fluid molecules over one another in a flowing liquid or gas." The internal friction of a fluid is Viscosity.

Liquids are much more "Viscous" vs gases.

If a fluid moves around a spherical solid with streamline flow, or a spherical solid moves through a fluid at rest, experiments show that the force of the fluid friction is directly proportional to the relative velocity of the fluid and the sphere. Thus the greater the velocity of the sphere with respect to the fluid, the greater the force of friction. Friction, as we all know, makes HEAT.

The viscosity of a liquid decreases, as the temperature rises, for the cohesive force between the molecules of a liquid determine its viscosity. For this reason Lubricating oils should be selected on the basis of their viscosity over a range of operating temperatures of a machine.

All that being said:

1) You increase the rpm of your engine, even under a light load condition, the temperature of the bearing shell goes up. (A LOT!).

2) You need to remove the heated oil quickly from the bearing and at the same time maintain a cohesive film of lubricant called "hydrodynamic lubrication".

3) The most common method of lubrication for sleeve (Journal) bearings
is by the hydrodynamic method. When the two surfaces of a bearing
and shaft move rapidly relative to one another, the oil is carried
along the shaft to fill the gap between shaft and bearing. When
the moving components become completely separated by a cohesive
film of lubricant, hydrodynamic lubrication occurs. Hydrodynamic
lubrication prevents wear in moving parts, as there is no metallic
contact between them. The bearing metals can last for a long time.

4) During starting time, the rotating shaft does not have sufficient
speed to pick up the lubricant. The film separating the moving
surfaces is very thin - with only the thickness of a molecule. This
is a condition called boundary-layer lubrication. With this
condition, friction losses increases, producing heat, which raises
the temperature of the lubricant, thereby reducing its viscosity so
that the load-carrying capacity of the film is even lower. In worst
case conditions, the surfaces can even seize together.

So what do we know:

a) The oil needs to have sufficient viscosity to not break down under heat.
b) The oil needs to have a specific viscosity to easily start Hydrodynamic Lubrication
c) The engine needs to have large enough clearances to allow the heated oil to escape
from the bearing surface.
d) The oil pump needs to have sufficient pressure and volume to maintain the Hydrodynamic Lubrication process under high RPM/load conditions.
e) The oil viscosity needs to be selected based on the environmental conditions.

I say ALL FOUR conditions.

Tom Vaught

 

Well, now I know to keep my mouth shut.

But since it's open at the moment, how about some examples of how "What we know" a-e, apply to #2-3 in the first post.

 

I like Joe's Info: (RPM, HP, and Oil Temp vs oil viscosity) Read his whole website

http://www.joegibbsracingoil.com/trainingcenter/viscosity.html

Once you look at the chart you can look up the oil specs here:

http://www.joegibbsracingoil.com/products/engineoils.html

Tom Vaught

It would be nice to know what he calls "Standard Clearances"

 

What about diesel oil and zddp?

 

Diesel oil is the same as the others now. NO MORE ZDDP.

 

Just when I think I can use my degree to help someone out... bam! Just kidding. That is a very well thought out reply. I would love to have some temperature probes at different points of my rotating assembly just to see the pressure/temperature they see. Basically a bunch of transducers with thermocouples attached.... good luck getting that to work easily. Nice write up!

 

Food for thought, SSJ50DRIVER:

I made a bearing rig (Ford Research Work) some years ago, to determine bearing temperature vs oil viscosity vs bearing clearance vs point of entry effects.

1) The connecting rod normally travels around the crankshaft rod journal. I held the rod/ rod bearing and rotated a single rod journal using a "Lab View" controlled electric motor.

2) I fed the rod journal from the opposite end of the rig from the motor drive. The rod journal was supported by high speed Vortech Supercharger bearings on either side.

3) The connecting rod was a Carrillo piece with direct pin oiling from the rod journal. I could use that passage to route a thermocouple down the length of the rod to a slight
indent in the back side of the tested bearing. (No wires flying around from reciprocating
motion).

4) The oil was pumped by an "Oil Cart", (an oil pump rig driven by a variable speed electric motor with a oil heater/ cooler to maintain precise oil temps) through a line to the connecting rod.

5) Lab View had the ability to control the Bearing Rig speed, the oil pressure, and the oil temperature while at the same time collecting thousands of samples for data analysis.

It is amazing just how hot the bearing shell/ oil gets going from Idle to 3000 rpm, much less at higher speeds. Because there was no firing loads on the rig, this temp increase is purely from rotational friction between the journal surface, the oil, and the bearing surface.

It was very "eye-opening" to me, even after years of racing background. I would say that proper engine oiling design, oil type, viscosity, and bearing clearances all play major parts in a successful engine combination. What works in a drag engine most likely will not be the same combination in a circle track or road race application.

Let the engine tell you what it wants.

Tom Vaught

 

Very informative Tom. That must have been a treat to see and do. I'm kind of jealous. Great posts man.

 

Tom, I've got a few questions:

1) My understanding is that the speed of the oil moving past the bearing/journal surfaces directly impacts the thickness of the shear layer, the layer of oil that remains stationary next to the metal surfaces, and that, to some degree, the thicker shear layers contribute to higher internal pressures in the oil (more pressure to keep the hydrodynamic wedge functioning and the metal surfaces from touching). Is that correct, or do you have a better explanation for that? It's been very difficult for me to find someone who has experience with these sorts of things in an experimental (and not strictly academic) setting.

2) You said the fixture you were using was made to test point of entry effects. Did you study point of exit effects? I ask this because of a conversation I had on another site about a certain Oldsmobile builder's tendancy to "notch" connecting rods (near the balance pad) for more oil flow, and I thought that there could be localized effects on the area around the notch, which also happens to be the area with the least loading under combustion, but the most loading on the compression stroke and at TDCE. Would it be safe to say that increasing the totality of the side clearance on the rods would be better than increasing the clearance on a small part of the rod's big end?

Thanks in advance, and please let me know if I'm way off base on my understanding.