How to Choose LS Engine Bearings for a Rebuild
In Summary
- Bearings are among the cheapest parts in an LS rebuild and the most likely to end one early, so the old set should be read carefully before the new set is ordered.
- Main and conrod journals are common across the LS family at 2.559 inches and 2.100 inches, which makes selection a question of material, clearance and load rather than fitment.
- Oil clearance is the decision that matters most on a high horsepower build, because it sets the thickness of the oil film the crank rides on and controls how much oil leaves the bearing.
What Can the Old Bearings Tell You?
Pull the caps before you order anything. A used bearing is a record of how the engine has been running, and it will often point at a problem that has nothing to do with the bearing itself.
Even, dull grey wear spread across the shell is what you want to see. Copper showing through the surface means the overlay has worn away and the bearing was living on borrowed time. Fine scratches with dark specks embedded in them point to dirt in the oil, which is usually a filtration or cleanliness issue rather than a bearing issue.
Wear concentrated at one edge of the shell suggests a tapered journal, a bent rod or a housing bore out of alignment. A smeared, blued or partly wiped surface points to oil starvation or heat.
Keep the old shells in order as they come out and note the position and which half each was. That map tells you more than any single measurement.
What Does an LS Rebuild Actually Need?
A Gen III or Gen IV LS runs five main bearings, eight pairs of conrod bearings and five cam bearings. The thrust flanges sit on the centre main at number three, which is where crankshaft end float is controlled.
Main journals measure 2.559 inches and rod journals measure 2.100 inches, the same as a large journal small block Chevrolet. Complete kits cover mains, rods and cam bearings under one part number, which suits a standard rebuild. Buying the sets separately makes more sense when you are mixing materials or chasing a specific clearance.
Stock Replacement, Performance or Race?
Standard replacement bearings use a bi-metal construction, with an aluminium alloy layer on a steel backing. They run quietly, tolerate debris well and are correct for a stock or near stock rebuild that will live on the street.
Tri-metal bearings add a copper-lead layer beneath a soft overlay. They carry more load and handle higher cylinder pressures, which makes them the sensible step up for a cammed engine or a mild boost combination.
High performance and race series bearings are tri-metal with harder backings, tighter wall tolerances and often a narrowed shell that reduces edge loading at high rpm. Coated versions add a dry film that protects during start-up and momentary oil starvation, which earns its money in boosted and high rpm engines.
Race bearings buy margin rather than power. Margin is what keeps an expensive crankshaft and engine components alive when something briefly goes wrong.
Why Does Oil Clearance Decide the Build?
The crank never touches the bearing in a healthy engine. It rides on a wedge of pressurised oil, and clearance sets how thick that wedge is and how quickly oil escapes from the ends of the bearing.
The long standing rule of thumb is 0.001 inch of clearance for every inch of journal diameter. On an LS that works out at roughly 0.0025 inch on the mains and 0.0021 inch on the rods. Performance builds commonly add another 0.0005 inch to allow for higher oil temperatures, greater deflection and thinner oil under load.
Go too tight and the film collapses. Go too loose and flow through the bearing climbs steeply, because the volume leaving the bearing rises with roughly the cube of the clearance. That shows up as low hot oil pressure, higher oil temperature and a pump that cannot keep up.
On a high horsepower build, clearance, oil viscosity and oil pump components have to be chosen together, because extra clearance suits a heavier oil and a pump with the volume to feed it. Extra clearance shells, marked with an X in most catalogues, exist for exactly this.
How Do You Set Clearance Properly?
Measure it. A micrometer reading to 0.0001 inch and a dial bore gauge will give you real numbers. Plastigauge is best used as a cross check rather than the primary method.
Torque everything before you measure, including the side bolts on the LS main caps. Those bolts pull on the cap and change the bore, so a clearance measured without them is meaningless.
Measure every position rather than assuming the crank is uniform. Undersize bearing shells at 0.001 inch and 0.010 inch let you correct a single journal that measures out of the group. Check crank end float at the thrust while you are there, and use a proper assembly lube on every shell before the engine turns over.
What About Cam Bearings?
Cam bearings are cheap and awkward to change, so they belong in the same job. The set has to match the block. First design blocks from 1997 to 2003 use housing bores of 2.3260 to 2.3280 inches at positions one and five, while second design blocks from 2004 on use 2.3460 to 2.3480 inches. Ordering on year alone catches people out.
Performance and coated cam bearing sets are worth a look for high spring pressure, high rpm or boosted engines. Whichever set you choose, fit them with the correct tool and line the oil holes up exactly. A blocked cam bearing feed is a quiet way to ruin a fresh engine.
Get the bearings right and the rest of the build has something solid to sit on. Talk to the team at Malex Motorsports about what your combination needs before you order.
FAQ
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Glossary
Main bearings: The five shell bearings that support the crankshaft in the block. On an LS the thrust flanges are carried on the centre main at number three.
Conrod bearings: The eight pairs of shells that sit between the big end of each connecting rod and the crankshaft rod journal.
Cam bearings: The five bearings that support the camshaft in the block. LS sets are split between first design and second design blocks according to the housing bore at positions one and five.
Oil clearance: The gap between the journal and the bearing surface, filled in service by a pressurised film of oil. It is the single most important dimension in bearing selection.
Bi-metal bearing: A bearing with an aluminium alloy layer bonded to a steel backing. Quiet, tolerant of debris and suited to stock and near stock rebuilds.
Tri-metal bearing: A bearing with a copper-lead layer between the steel backing and a soft overlay, giving higher load capacity for performance and boosted engines.
Narrowed shell: A bearing made narrower than standard to reduce edge loading and increase oil flow at the sides, commonly used in high rpm builds.
Extra clearance bearing: A shell machined to give around 0.001 inch more clearance than standard, usually identified by an X in the part number.
Undersize bearing: A thicker shell, offered in sizes such as 0.001 inch and 0.010 inch under, used to restore correct clearance on a reground or slightly worn crankshaft.
End float: The permitted fore and aft movement of the crankshaft, controlled by the thrust flanges on the centre main bearing.
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