Bearings are the cheapest parts in your short block and the ones most likely to end it. A wrong groove, a mis-set clearance, or a bearing that never gets clean oil will take out a crankshaft in minutes. The good news with a Pontiac is that the family is simple once you know two numbers — main journal size and rod journal size — and those two numbers drive every bearing decision you make.

An engine bearing never touches the crank when it's running right. A wedge of pressurized oil holds the journal off the bearing face — that's hydrodynamic lubrication. The bearing's real jobs are to build and hold that oil film, to survive the split-second of metal contact at startup, and to embed the grit that gets past the filter instead of scoring the crank. A few features make that happen:

• Crush — each shell stands slightly proud of the bore parting line. Torque the cap and that extra height is squeezed in, locking the shell tight to the housing so it can't spin or move. Too little crush and the bearing walks; too much distorts the bore.
• Spread — the shell is made a hair wider than the bore diameter so it snaps in and stays put during assembly. It is not a clearance adjustment.
• Locating tang (lug) — the notch on the shell drops into the housing to index the bearing and line up its oil hole. It stops rotation; it does not carry load.
• Oil hole & groove — must line up with the block/rod feed passage. The upper main shell carries the feed hole and (usually) the groove, because the upper half sees lighter load.
• Eccentricity — the bore isn't a perfect circle. Wall is thickest at the crown and thinner near the parting line, which opens up film thickness where the journal unloads and keeps the wedge alive.
• Chamfer / fillet clearance — the edge of the shell is relieved to clear the radius where the journal blends into the cheek. Reground and aftermarket cranks often have a larger fillet radius — if the bearing edge rides up on it, you get edge loading and no clearance at the parting line. This is why performance sets are often chamfered or narrowed.

Bearing selection is a trade between two properties that pull against each other: load capacity (fatigue strength) and conformability/embedability (the ability to bend around a slightly imperfect journal and swallow debris). The construction determines where a bearing lands on that scale.

Main Bearings

The Pontiac uses a 5-main bottom end sized 3.00" (326/350/389/400) or 3.25" (421/428/455). Ordered as a set of 5, they include the thrust bearing and the grooved/oil-fed uppers. Two Pontiac-specific points matter:

• Thrust is on the #4 main — not the rear. The #4 bearing carries fore/aft crank load (from the converter or clutch) and sets end play. Watch this on aftermarket cranks: some run slightly longer than a factory Pontiac crank, so the journal fillet can contact the edge of the #5 shell before the crank ever reaches the #4 thrust face. Check that end play is actually being controlled at #4, and relieve/verify #5 clearance if it isn't.
• Oiling. Large-journal (421/428/455) cranks are cross-drilled from the factory for continuous rod feed; small-journal cranks are not. That's why small-journal builds so often use grooved (3/4 or full) upper mains — the groove feeds oil to the rod journal through more of the crank's rotation and largely does the job cross-drilling would. More on grooving below.

Rod Bearings

Stock Pontiac rod journal is 2.25" across the whole family, so factory-journal rebuilds use a Pontiac 2.25" rod set. Rod bearings are normally ungrooved — the full lower face is needed to carry the firing load, and the crank's own passage feeds them. The wrinkle is strokers: many Pontiac stroker kits are built on a 2.200" big-block-Chevy rod journal so they can use readily available BBC rods and bearings. If your kit uses a 2.20" BBC journal, you order BBC rod bearings (Clevite CB-743-family), not Pontiac rod bearings — a common ordering mistake. On stroker cranks you'll also see narrowed (N) bearings to clear the crank cheeks/fillets and extra-clearance (X) bearings that add ~.001" for high-rpm oil film. Know which your kit calls for.

Cam Bearings

The Pontiac cam rides in 5 cam bearings, and here's the trap: they are a graduated (stepped) set — the journals step down in diameter from front to back, so each bearing is a different size and must go in its correct position and orientation with its oil hole indexed to the block passage. A universal Pontiac cam set (e.g. Clevite/MAHLE SH-292-S, 1963–81, 265–455) is the standard replacement. Notes for the machine shop:

• Oil-hole alignment is critical — a cam bearing turned so its feed hole is blocked will starve a lifter bank.
• Aftermarket / oversize blocks use larger-OD cam bearings (e.g. +.010" OD sets, or 2.282" journal sets for blocks line-bored specifically for them). The block must be machined for these — don't mix.
• Roller cam bearings exist for high-effort valvetrains; some are splash-lubricated and let you block cam-bearing oil feeds to cut aeration and windage — only do this if the rest of the oiling system is set up for it.

The groove in a main bearing is an oil highway to the rod journals — but every bit of grooved surface is surface that isn't carrying load. That's the whole trade. Grooving is described by how far it wraps the shell:

Rule of thumb: the bottom (cap) half of the main takes the firing load, so you want it solid; the top half unloads on the power stroke, so that's where the groove goes. Match your groove choice to your crank's oiling: a factory cross-drilled 455 crank is happy with less grooving; a small-journal, single-hole 400 crank benefits from a 3/4 or full groove. Whatever you choose, the rod bearing itself stays ungrooved.

In practice, that's why the Pontiac main sets Butler stocks come in different groove styles: the Clevite MS-483G (3.00" main) is a half-groove set, the Clevite MS-496P (3.00") and MS-667P (3.25") are full-groove, Federal Mogul's Competition H-14 comes 3/4-groove, and King HP offers a standard-with-extra-clearance option. Pick the groove to match the crank and the rpm, not just what's on the shelf.

Oil clearance is the gap between journal and bearing, and it sets the oil film. Too tight and the film is squeezed out — metal touches, the bearing wipes, oil pressure and temperature climb. Too loose and the film can't build pressure — you throw oil off the rods, lose pressure, and hammer the bearing. The classic starting point:

That's a baseline, not gospel. Higher rpm, more power, higher oil temps, and thinner oils generally want a touch more clearance and thicker film; tight street engines on heavier oil can live a bit tighter. On a street/performance Pontiac, rod and main clearance is traditionally set at .002"–.003" — safe, long-lived, but it sprays a lot of oil into the crankcase. For an all-out drag combination where you're chasing every bit of power, you can run them as tight as .0015"–.0025" — but only if the crank and rod tolerances are dead-nuts on. Always measure; never assume the bearing's marked size gives you the clearance you want on a reground journal.

Clearance also ties straight into your oiling strategy — pump volume, restrictors, and viscosity all assume a known clearance. If you're changing bearing clearances, revisit the oil pump & oiling system guide and the oil restriction guide so the whole system stays in balance.

When a crank is turned down to clean up the journals, you order bearings in a matching undersize — the bearing is thicker to make up for the smaller journal, so clearance stays correct. Common steps are Standard, .010", .020", .030" under. Match the undersize to how far the crank was ground on that journal (mains and rods can differ). "Oversize" on a bearing usually refers to a larger outer diameter for a line-bored housing (mains) or an oversize cam-bearing bore — a different axis from journal undersize, so read carefully.

Clevite part numbers pack the spec into the suffix. Decoded, the pieces you'll see on Pontiac/stroker bearings mean:

The real-world bearing questions our engine techs field most often, and the short answers we give.

A starting-point cross-reference for the Pontiac bearings Butler stocks — sizes available in Standard through .030" under unless noted. Confirm application and undersize before ordering.

Journal sizes, thrust location, clearance ranges, and part numbers reflect Butler Performance build data and published Pontiac V8 specifications. Part numbers and availability are subject to change — confirm current pricing and stock on butlerperformance.com. Always confirm actual journal sizes by measurement and set final running clearances to your specific crankshaft, oil, and rpm target.

Stock Rebuild vs. Butler Performance Clearances