Main and rod bearing materials

[spasm3]

I'm planning a rebuild for a saturn engine. Looking at bearings, i see the old mainstay , clevite/michigan 77 bearings. These bearings are the trimetal lead overlay bearings. Looking at sealed power bearings they are aluminum bearings.
i know both brands are quality but what are the advantages of aluminum bearings over the lead? or vice versa?

 

[redbone3]

I suspect the contact metal on all of them is babbitt. As for the other parts of the bearing.....well, aluminum is cheaper than copper. For a Saturn engine I would go with the same type as the original (Some engineer hopefully correctly figured out the correct expansion ratio and specified the appropriate bearing originally)

 

[MolaKule]

I like the oil hydrodynamics of the Sealed Power Bearings and the fact they use an aluminum alloy, which should transfer heat better than the old steel-backed lead-copper overlay type bearing.

 

[turtlevette]

Originally Posted By: MolaKule
I like the oil hydrodynamics of the Sealed Power Bearings and the fact they use an aluminum alloy, which should transfer heat better than the old steel-backed lead-copper overlay type bearing.


How would the hydrodynamics be different? A surface is a surface.

Isn't oil flow past the outer layer the primary source of heat transfer.

 

[bluestream]

Originally Posted By: redbone3
I suspect the contact metal on all of them is babbitt. As for the other parts of the bearing.....well, aluminum is cheaper than copper. For a Saturn engine I would go with the same type as the original (Some engineer hopefully correctly figured out the correct expansion ratio and specified the appropriate bearing originally)


Hopefully it wasn't the same engineer that forgot to add the oil drain holes for the pistons...

 

[MolaKule]

Originally Posted By: turtlevette
Originally Posted By: MolaKule
I like the oil hydrodynamics of the Sealed Power Bearings and the fact they use an aluminum alloy, which should transfer heat better than the old steel-backed lead-copper overlay type bearing.


How would the hydrodynamics be different? A surface is a surface.

Isn't oil flow past the outer layer the primary source of heat transfer.




Quote:
Sealed Power main sets feature a patented Ramp and Flat® Contoured Flange design. Hydrodynamic profiles on the flange surface wedge oil onto the surface of the flange face, significantly reducing wear, extending bearing life and doubling thrust load capacity.


Heat is carried away from bearings by two methods: 1.) Convection (oil flow) cooling and 2.) Conduction to the block.

 

[turtlevette]

Originally Posted By: MolaKule


Quote:
Sealed Power main sets feature a patented Ramp and Flat® Contoured Flange design. Hydrodynamic profiles on the flange surface wedge oil onto the surface of the flange face, significantly reducing wear, extending bearing life and doubling thrust load capacity.


Heat is carried away from bearings by two methods: 1.) Convection (oil flow) cooling and 2.) Conduction to the block.

That's just some channels milled in the face of the thrust surface. The thrust bearing is not a high load area anyway.

The oil flow on the bearing surface must account for 90% of heat transfer, so I doubt a higher Q rate bearing material helps that much.

Actually thinking about it some more, heat is being created in the cylinder liner migrating down to the main saddles to the bearing saddles and its going the other way. Into the bearing. So it would help to have a more insulating material on the bearing.

 

[Quest]

http://kingbearings.com/files/Engine_Bearing_Materials.pdf

 

[spasm3]

Thanks!

 

[Trav]

Both types are steel backed so i don't think the thermal properties would be too different, copper is also a good conductor.
In everyday engines aluminum bearings are holding up very well and living longer, not so in high HP/output engines where the bearings can really get pounded.

I would go with the aluminum 100% for the Saturn engine, the tri metal live longer in high HP applications but its still a relatively short life, the aluminum in a normal engine will have a much longer lifespan.

http://www.nmcadigital.com/2013/12/29/how-to-spec-an-engine-bearings/

 

[A_Harman]

OE bearings in that engine would have been aluminum.
Leaded bronze bearings can withstand higher unit loadings than aluminum bearings, but this is really only of interest in racing applications. The standard aluminum-lined bimetal bearings are fine for an I4 running on the street.

 

[Kestas]

Copper bearings are typically made with sintered copper powder on a steel backing, thew pores are infiltrated with lead, and the whole piece is then coated with a thin layer of tin. The tin acts as a break-in layer, for the same reason aluminum pistons are coated in tin.

The aluminum bearings I've seen are made with a layer of aluminum on steel backing. The aluminum has a fine dispersion of silicon particles.

I don't believe aluminum bearings are better. I believe they're used because automakers are trying to take out all lead in vehicles. Aluminum bearings suffer from galling issues, which can cause a bearing to catastrophically fail more easily, than copper-lead surfaces.

When it comes to thermal transfer, copper does a much better job than aluminum, if it was a factor in the pins and mains.