Section 1 Bearings & CAT Engines Flashcards
What are the two main bearing constrution types?
Bi-Metal: half-shell bearing consists of a steel back layer and an aluminum-based alloy running surface layer.
Tri-Metal: half-shell bearing consists of a steel back with an aluminum-based or copper-based alloy layer and a thin lead-tin overlay covering the alloy layer
What are the 5 factors that are used in the selection if bearing materials?
Compatibility: is the ability of the bearing material and the journal surface to function properly together in a bearing system, especially during periods of momentary contact.
Strength: in a bearing material allows the bearing to retain its shape and to withstand the oil film pressures and loads from momentary contact with the journal.
Wear resistance: of the bearing material ensures that the materials are present on the bearing surface at the end of useful life therefore the properties of the bearing are consistent throughout useful life.
Conformability: is the ability of a bearing material to adapt or conform to the shape of a journal.
Embedability: of the bearing material allows it to absorb small particles of debris.
What are the layers of a main bearing construction?
Steel back: provides strength, overall shape retention, and support for alloy bearing layer.
Bearing alloy layer: provides strength to withstand heavy shock loads of engine operation, soft for good embedibility and comfortability and compatible w/ steel.
Lead-tin overlay: thin often 0.0006in-0.0012in thick, heal over when scratches from small particles happen. Big particles cause problems for bearings!!!
Tin flash: only for some tri-metal, 0.00004-0.00012in thick final layer protects against corrosion during storage, light or dark grey color, cosmetic scratches are normal.
What are the bearing phsical features?
Nomenclature
For picture refer to media #sebf8009
A)Tab slot on ID surface
B)Edge of bearing
C)Bottom half
D)Top half
E)Bearing surface
F)Oil Groove
G)Oil Hole
H)Locking Tab on OD surface
I)Mating face
What is the nomenclature for a connecting rod bearing?
For picture refer to media #sedf8009
A) Tab Slot on ID surface
B) Edge of Bearing
E) Bearing Surface
H) Locking tab on OD surface
J) Mating face
What is bearing spread?
Bearing spread simply means that the outside diameter of the bearing at the mating faces is slightly larger than the actual diameter of the bore.
What is bearing crush?
Bearing crush insures complete contact between the bearing and the bearing bore. This complete contact contributes to better heat dissipation and prevents movement of the bearing in the bore.
(Q) Bearing Crush Picture reference
Why is the lubrication system an important factor in bearing performance?
Reduces friction
Provides an oil film cushion that keeps metal to metal contact to a minimum
Cools engines parts
Cleanses the engine from particles and debris
What does an oil film do?
Lubricates
Cools
Cleans bearings
Is a critical factor in bearing life
How does oil viscosity relate to the main and connecting rod bearings?
It provides a resistance in oil flow or changes shape.
Goes hand in hand with the oil film.
How does low oil level affect a the bearings?
Messes with oil temp
viscosity
causes severe bearing damage
Why are oil filters so critical to bearings?
Keeps dirt and particles out of oil and bearings.
Improves bearing life
How does cooling system affect bearing performance?
Keeps oil at right temp
What are the 2 common signals when bearings are damaged?
Engine knocking noise
Low oil pressure
Why does low oil pressure mean there is bearing damage?
Bearing wear increases causing bearing clearance to increase between the bearing and crankshaft.
Causing more oil to flow out the sides of the bearing and therefore decreasing oil pressure.
