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421-428-455 Main Bearings
Pontiac V8 421-428-455 Main Bearings
The 3.25" Main Family — 421-428-455 Main Bearings for Pontiac V8s
Pontiac's big-journal blocks — the 421, 428 and 455 — use a 3.25" main journal, and that alone separates this bearing family from everything on the 326-400 side. A 455 main bearing set will not go in a 400, and the reverse is just as true.
Butler stocks this group from Clevite and Federal Mogul: tri-metal sets in standard and undersizes, Federal Mogul performance mains, and a Clevite race main with half upper and lower grooving and .001" of extra clearance built in for engines that want more oil at the bearing.
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More About 421-428-455 Main Bearings
1. What makes this its own family
The 421, 428 and 455 share a main journal size, so they share a bearing. Nothing else in the Pontiac V8 line does.
| 3.25" mains | Every set on this page is cut for the big journal. The 326, 350, 389 and 400 use a 3.00" main and have their own page. |
| One set covers three engines | Clevite and Federal Mogul both catalog these as 421, 428 and 455 sets, which is why a 428 owner and a 455 owner order the same box. |
| Sold as a set | These are complete main bearing sets with the thrust bearing, not individual shells. |
2. Street tri-metal, performance, or race
Three different intents live on this page, and the price of getting it wrong is either a noisy engine or a hurt crank.
| Standard tri-metal | Federal Mogul's standard main bearing sets for 421, 428 and 455 are the rebuild answer — the set for a stock or mild engine going back together. |
| Performance mains | Federal Mogul also catalogs a performance main bearing for these engines. That is the step for a street/strip car that is going to see rpm. |
| Clevite race with extra clearance | Clevite's race main for the 421, 428 and 455 uses half upper and lower groove and adds .001" to your main clearance. Butler's copy states it plainly: this bearing will add clearance to your mains by .001". That is a deliberate build choice for a high-rpm engine, not a substitute for correct machining. |
3. Reading the Clevite suffix
Clevite's part number carries the spec, which is genuinely useful once you know the letters.
| H series | Clevite's own guidance says the H series is the one to start with when you are unsure. Medium eccentricity, high crush, enlarged chamfers for greater crankshaft fillet clearance, no flash plating so it seats better, and intended for engines running the mid-to-high rpm range. |
| P series | Typically the greatest eccentricity, high crush for maximum retention, and most are fully grooved to maximize oil flow to the rod bearings. Clevite points these at extremely high rpm where rod bore close-in becomes severe. |
| X and XX | X means the bearing has .001" more oil clearance than standard; XX means .002" more. |
| N, D and K | N is a high-performance narrowed bearing for greater crankshaft fillet clearance, D means the bearing has a dowel hole, and K is a Tri-Armor coated bearing. |
4. Sizing to a turned crank
These sets are stocked in undersizes for the same reason every bearing is.
| Order to the grind | Standard, .010, .020 and .030 are catalogued across the Clevite and Federal Mogul sets here. The crank's finished size decides which one, not the engine's year. |
| Fillet clearance | If the crank was ground with oversized fillets, that pushes you toward a bearing with enlarged chamfers or a narrowed bearing. Say so when you order. |
| Check the clearance you get | Plastigage or mike it. An extra-clearance bearing on a crank that was already ground generously stacks up fast. |
Have the crank's measured main journal sizes on paper before you order. On the big-journal Pontiacs that one number answers most of this page by itself.
Not sure what your Pontiac needs?
Call our tech team at 866-762-7527. Tell us your engine, heads, car, and power goal, and we will put the parts together as one combination that works.