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BOP Pontiac 3.00" Main Single Lip Viton 2pc Rear Main Seal (301, 326, 350, 389, 400) BOP-RMS01
BOP-RMS01
Pontiac 3.00" main 2-piece single-lip Viton rear main seal. Can be installed with the crank in the engine. Fits 1959-79 326-400 and 1979-81 265/301 (early 347/370 when trimmed). 421/428/455 use BOP-RMS02.
Pricing:
$49.95
Description
Read before you order — this is the 2-piece seal
- 2-piece, single-lip Viton. Can be installed with the crankshaft still in the engine (oil pan, pump and windage tray off) using BOP's crank-in procedure.
- Fits: Pontiac 3.00" main blocks — 1959-79 326, 350, 389, 400 and 1979-81 265/301. Fits early 347/370 when trimmed to fit.
- Wrong main size? 421/428/455 (3.25" main) use BOP-RMS02.
- Crank doesn’t measure exactly 3.00" or 3.25"? Order by engine, not by your measurement: all 326-350-389-400 use the 3" main journal seal (RMS01 / RMS18); all 421-428-455 use the 3.25" seal (RMS02 / RMS19). The seal rides on the crank’s rear seal surface, not the main journal — BOP lists that sealing diameter as 3.188" ± .003" for the 3.00" seals and 3.437" ± .003" for the 3.25" seals. If your crank or seal groove is out of spec, call before installing.
- Rebuilding with the crank out? The dual-lip 1-piece BOP-RMS18 is Butler's recommended seal.
- Not for Oldsmobile 403 — see BOP-RMS03.
2-Piece vs 1-Piece — Which Seal?
| 2-Piece (single lip) | 1-Piece (dual lip) | |
|---|---|---|
| 3.00" main (326-400, 265/301) | BOP-RMS01 | BOP-RMS18 |
| 3.25" main (421/428/455) | BOP-RMS02 | BOP-RMS19 |
| Seams | Pre-cut in halves | Cut once, on the designated cut dot, at install |
| Lip | Single lip | Dual lip — second lip acts as a wiper on the crank |
| Crank in the engine? | Yes — BOP includes a crank-in procedure | No — the crankshaft must be removed |
| Best for | In-car repair with the pan off | Engine rebuild with the crank out |
Installation Notes
- Dry fit the seal in the block and cap (no sealer, no crank) and look through the bore — the ends must meet with no gaps or distortion, and the seal must not flex or bulge when the cap is installed. If it does, trim slightly with a sharp utility knife. Fitment before installation is what makes it seal; too tight means more drag.
- In-car (crank in): fill only the two anti-rotation holes in the cap with high-temp silicone. Crank out: fill all four anti-rotation holes (block and cap) level with the bottom of the groove — do not fill the groove.
- Put a thin film of high-temp silicone on the seal ends only. Do not coat the back of the seal, the groove or the seal cavities — that over-compresses the lip and wears it out early.
- Note the seal orientation shown on the instruction sheet, and lightly oil the lips before the crank goes in.
- Let the assembly sit overnight so the sealer cures undisturbed.
- Rear main cap, stock fasteners: 120 ft-lbs with engine oil. With ARP or other aftermarket hardware, use that manufacturer's torque and lube.
- Butler runs these Viton seals on serrated factory cranks with no issues. Only extremely sharp serrations need attention — buff lightly with emery cloth without removing material that changes the crank's geometry.
Why Viton over rope: the dual-lip Viton seal acts as a wiper on the crank. Rope seals are good quality today and work when installed correctly, but Butler considers them far inferior to a dual-lip Viton seal — the BOP Viton seal is Butler's go-to.
Instructions & Tech
RMS01 / RMS02 Instruction Sheet (crank in and crank out) | Viton Rear Main Seal Guide
Not sure which one you need? Ask a tech question or call 866-762-7527 before you order.
Details
- BOP-RMS01
- BOP-RMS01
- BOP
- New
Categories
Shipping Information
- Item Requires Shipping
- 0.3 lbs.
Customer Reviews
Total Reviews (1)
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Reviewed by: keith05/10/2019 09:58PM
Product ownership: A year or longer
Purchased from: Butler Performance Inc.
Comments:
nice