Engine Bearings More than Just a Curved Piece of Metal
Engine bearings aren’t just one piece of the engine; they are an extremely vital part.
Tucked away deep inside the engine, most people don’t give them a thought, at least
until they want to make serious horsepower. This article is Part One of engine bearing
basics and covers bearing types and materials.
Your engine uses something we engine experts call “insert bearings”, not to be confused
with “poured Babbitt” bearings used in engines of the 20’s, 30’s, 40’s and early 50’s.
Insert bearings are designed to be replaced as they wear out, saving the much more
expensive crankshaft from wear. As you may know, they are sold in service sets and
often in several undersizes to accommodate worn and re-ground crankshafts.
When you put the two halves of a connecting rod pair or a main bearing pair together, it
would appear you have a 360 degree circle. Actually, the bearings are designed with
both a parting line relief and something called eccentricity so that the bearing is able to
function as designed. You can learn more about the design and engineering of bearings
from MAHLE Clevite’s on-line eLearning course on engine bearings.
When an engine is running, the crankshaft doesn’t touch the engine bearings, but run on
a thin film of oil. The oil film under firing loads can be as thin as .0002” and still provide
protection to both the bearing and the crankshaft. This entire topic, oil film thickness,
bearing clearances, oil pressure and viscosity are huge complicated subjects and again
the eLearning class will help with more detailed concepts. What I can tell you is: use the
best motor oil you can and warm your engine up before you start to hammer on it.
Virtually all modern automobile engines (late 90’s and newer) use bi-metal Aluminum
bearings from the factory. The construction is a steel back with a layer of silicone-
aluminum facing the crankshaft. Car manufacturers have moved to these bearings
because they are lead-free, economical to manufacture, are extremely hard and wear
almost forever. These bi-metal AL bearings will last the life of the engine in normal
Virtually all performance bearings are constructed using an older technology called tri-
metal construction. Essentially, it has a steel back, a copper-lead intermediate layer and
a surface layer of a soft material like Babbitt. This construction, perfected by Clevite
works very well on performance engines because it is a more forgiving and
accommodating material than hard SI-AL stock bearings.
Race and performance engines see crankshaft deflection, rod bore distortion and very
thin oil film thickness under severe loads. The softer Babbitt facing combined with
application specific geometry of the shells allows the crank to survive and the engine to
keep running long after the bi-metal Aluminum stock parts had failed.
Clevite offers a wide variety of Trimetal® bearings, P series stock replacement bearings,
H series racing bearings, V series racing bearings and K series coated bearings.
The most popular selection for racers and those with performance engines is the H
series. It was developed for NASCAR and continues to be the #1 choice for NASCAR
teams. The geometry, construction and face material work very well in engines making
from 300 to 1800 horsepower.
They are available for a wide variety of performance engines including classics like the
409 Chevy, 455 Olds, 500 Cadillac, etc. If you’re unsure of your performance needs, this
is the place to start. You can also ask me of course for help and advice picking the
correct bearing for your engine.
K series coated bearings are a good choice for street rods and show cars that sit for
months without being run. The coating provides extra protection against “dry starts”.
Clevite has coated bearings from the K series all the way up to the “Nitro-V” series
bearings used in 8000 HP top fuel and funny cars.
Well this concludes Part One. Check in next week for Part Two when I dig into bearing
markings and failures. If you have any questions about what was covered in this article
don’t hesitate to ask!