Complete replacement of main bearings on a 1966 Corvette 327ci V8, requiring engine removal, crankshaft extraction, bearing replacement, and reinstallation with precision measurement.

Warnings

Tools required

Parts

• Main bearing set (standard or appropriate oversize) × 1 — Use OEM specification
• Thrust bearing set (rear main position) × 1 — Use OEM specification
• Main bearing cap bolt set × 1 — Use OEM specification
• Oil pump gasket × 1 — Use OEM specification
• Oil pan gasket set × 1 — Use OEM specification
• Oil pan cork end seals × 2 — Use OEM specification
• Rear main seal (rope style) × 1 — Use OEM specification
• Front timing cover gasket × 1 — Use OEM specification
• Timing cover seal × 1 — Use OEM specification
• Harmonic balancer installation bolt × 1 — Use OEM specification
• Valve cover gaskets × 2 — Use OEM specification
• Intake manifold gasket set × 1 — Use OEM specification
• Exhaust manifold gaskets × 2 — Use OEM specification
• Water pump gasket × 1 — Use OEM specification
• Thermostat housing gasket × 1 — Use OEM specification
• Oil filter × 1 — PF25 or equivalent
• Engine assembly lubricant (moly paste) × 1 — Use OEM specification
• RTV silicone gasket maker (high-temp) × 1 — Use OEM specification
• Thread locker (medium strength) × 1 — Loctite 242 or equivalent
• Brake cleaner or carburetor cleaner × 2 — Generic

Fluids

• 5W-30 Conventional Engine Oil — 5 qt
• DEX-COOL Extended Life Coolant (Orange) — 10 qt

Preparation

1. Position vehicle on level concrete surface in well-lit workspace with adequate clearance for engine removal (minimum 8 feet clearance in front of vehicle).
2. Disconnect negative battery cable and secure away from battery terminal.
3. Drain engine coolant completely into suitable container by opening radiator petcock and removing lower radiator hose.
4. Drain engine oil completely and remove oil filter.
5. Remove hood by marking hinge positions and unbolting four hinge bolts with assistant support.
6. Remove air cleaner assembly completely.
7. Drain and disconnect automatic transmission fluid cooler lines if equipped, or drain manual transmission if applicable.
8. Label and disconnect all vacuum lines, fuel lines (relieve any residual pressure first), electrical connections, throttle linkage, and control cables from engine.
9. Remove radiator and shroud assembly after disconnecting upper and lower hoses.
10. Disconnect exhaust system at manifold flanges or head pipes.
11. Remove distributor cap and mark distributor position relative to block for reinstallation reference.
12. Support transmission with transmission jack or suitable stand from underneath vehicle.
13. Remove bellhousing-to-engine bolts and separate transmission from engine (may require removal of torque converter bolts if automatic).
14. Attach engine hoist with grade-rated chain to engine lifting brackets (intake manifold bolt positions on small block Chevy) and take up slack to support engine weight.
15. Remove motor mount fasteners from frame brackets.
16. Carefully lift engine from vehicle, using load leveler to adjust angle and clear firewall and radiator support. Have assistant guide engine during extraction.

Procedure

1. 1

   Mount engine on engine stand
   Lower engine onto engine stand and secure using 4 Grade 8 bolts threaded into bellhousing bolt holes. Torque stand mounting bolts to 50 ft-lb minimum. Ensure engine is balanced and stand is locked before releasing hoist.
2. 2

   Remove external engine components
   Remove remaining external components to access internal engine: water pump (4 bolts), fuel pump (2 bolts), alternator and brackets, power steering pump and brackets, valve covers (6 bolts each), intake manifold (12 bolts - remove end bolts first, then progressively loosen center bolts from outside to inside), exhaust manifolds (5 bolts each side), distributor (1 hold-down bolt), and oil filter adapter if present.
3. 3

   Remove timing cover and timing set
   Remove harmonic balancer by first removing center bolt (use breaker bar, bolt is torqued very tight). Use harmonic balancer puller to remove balancer from crankshaft snout. Remove timing cover bolts (7 bolts around perimeter). Remove timing cover and gasket. Verify timing marks on camshaft and crankshaft sprockets are aligned (dot-to-dot at 6 o'clock position). Remove camshaft sprocket bolt and slide both sprockets and timing chain off as assembly.
4. 4

   Remove oil pan and oil pump
   Rotate engine stand so oil pan faces upward. Remove oil pan bolts (perimeter bolts, typically 4 per side and 4 across front/rear). Carefully break oil pan gasket seal with gasket scraper if stuck. Remove oil pan. Remove oil pump pickup tube bolts (2 bolts) and remove pickup tube and screen. Remove oil pump mounting bolt and slide oil pump driveshaft out with pump.
5. 5

   Remove piston and rod assemblies
   Rotate crankshaft to position each piston at bottom dead center. Mark each rod cap and rod with cylinder number using metal stamp or marker (1-8, driver side front to rear is 1-3-5-7, passenger side is 2-4-6-8). Remove rod cap bolts from cylinder 1 (2 bolts per rod). Remove rod cap and bearing insert. Push piston and rod assembly up and out through top of cylinder using wooden dowel or hammer handle to gently tap on rod. Install rod cap back on rod loosely to keep caps matched. Repeat for all 8 cylinders. Place assemblies on clean workbench in order.
6. 6

   Inspect main bearing caps and mark orientation
   Inspect main bearing caps for factory numbering (should be numbered 1-5 from front to rear). If numbers are not visible, use metal stamp to mark each cap with its position number and mark orientation arrow pointing toward front of engine on both cap and block. The 327 has 5 main bearing caps. Cap orientation is critical; they are machined in position and not interchangeable.
7. 7

   Remove main bearing caps
   Remove main bearing cap bolts from all 5 caps (2 bolts per cap). Starting with front and rear caps (1 and 5), gently tap caps upward using soft-faced brass hammer or use main bearing cap puller. Remove caps and place on clean bench in order. Note that cap 5 (rear main) contains thrust bearing surfaces. Remove upper bearing shells from block by rotating them out of saddles. Keep bearing shells with their respective caps for inspection. Do not allow crankshaft to drop; support weight with wooden blocks on each rod journal.
8. 8

   Remove crankshaft from engine block
   With assistant support or using sling, carefully lift crankshaft straight up and out of engine block. Place crankshaft on padded workbench or V-blocks to prevent damage to journals. Support crankshaft at rod journals only, never on main journals.
9. 9

   Clean and inspect crankshaft journals
   Thoroughly clean all 5 main bearing journals and 8 rod journals with lint-free shop rags and brake cleaner. Clean all oil passages with rifle brush and compressed air. Inspect each main journal for scoring, scratches, discoloration, or wear. Check journal surfaces under bright light; they should be smooth and free of any imperfections.
10. 10

    Measure crankshaft main journals
    Using outside micrometer, measure each of the 5 main journal diameters at 4 points (90 degrees apart) and at 3 positions along journal length (front, center, rear of journal width). Standard main journal diameter for 327 small block is 2.4484-2.4493 inches. Record all measurements. Calculate out-of-round (difference between maximum and minimum diameter at same location) and taper (difference between front and rear measurements). Maximum allowable out-of-round or taper is 0.001 inch. If journals exceed this, crankshaft must be reground to 0.010, 0.020, or 0.030 undersize and appropriate bearings ordered.
11. 11

    Clean and inspect engine block bearing saddles
    Thoroughly clean all 5 main bearing saddles in block with brake cleaner and lint-free rags. Remove all old bearing material, gasket residue, and debris. Clean oil passages in block with rifle brush and blow out with compressed air. Inspect saddle surfaces for scoring, gouges, or damage. Saddles should be smooth with no raised material.
12. 12

    Measure main bearing bore diameter
    Install main bearing caps in their correct positions with bolts torqued to specification (factory spec for 327 2-bolt mains is approximately 60-70 ft-lb — verify against service manual). Using inside micrometer or dial bore gauge, measure bearing bore diameter of each of the 5 main saddles with caps installed. Measure at 2 positions 90 degrees apart (in-line with crankshaft and perpendicular to crankshaft). Standard main bearing bore should be 2.6484-2.6493 inches for standard bearings. Record all measurements. Calculate bearing clearance by subtracting crankshaft journal diameter from bearing bore diameter. Target clearance is 0.0008-0.0020 inch for standard bearings.
13. 13

    Select and prepare new main bearings
    Based on measurements from steps 10 and 12, select correct main bearing set (standard, 0.010, 0.020, or 0.030 undersize). New bearings come as upper and lower halves for each position. Note that position 5 (rear main) uses thrust bearing with flanges on upper and lower halves. Clean new bearing shells with lint-free cloth and solvent to remove protective coating. Do not wipe with shop rags as lint will embed in bearing surface.
14. 14

    Install upper main bearing shells
    Apply light coat of assembly lubricant to back of upper bearing shell (not bearing surface). Install upper bearing shell into each block saddle, ensuring bearing tang engages slot in saddle. Rotate bearing into position - do not force. Install all 5 upper shells. Note rear main upper bearing has thrust flanges on both sides.
15. 15

    Lubricate bearings and install crankshaft
    Apply liberal coat of engine assembly lubricant (moly paste) to bearing surface of all 5 upper main bearings. Carefully lower crankshaft into position in block, supporting at rod journals. Align crankshaft so it seats fully into all bearing saddles. Ensure crankshaft is centered and seated; it should rotate freely by hand with slight drag.
16. 16

    Install lower bearing shells in main caps
    Clean each main bearing cap bearing surface with brake cleaner. Apply light coat of assembly lubricant to back of lower bearing shell. Install lower bearing shell in each cap, ensuring tang engages slot. Do not install caps yet. Apply generous coat of engine assembly lubricant to bearing surface of each lower shell.
17. 17

    Check bearing clearance with Plastigage
    Place strip of Plastigage across each main bearing journal parallel to crankshaft centerline. Install main bearing caps in correct positions and orientation (numbers facing out, arrow pointing forward). Install cap bolts and torque to specification (approximately 60-70 ft-lb for 2-bolt mains — verify against service manual). Do not rotate crankshaft with Plastigage installed. Remove caps one at a time and measure width of flattened Plastigage using scale on Plastigage envelope. Clearance should be 0.0008-0.0020 inch. If clearance is too tight (less than 0.0008), bearing or journal size is incorrect. If too loose (greater than 0.0020), recheck measurements or try next undersize bearing. Remove all Plastigage residue with clean cloth.
18. 18

    Perform final main bearing installation
    After confirming clearances are correct, remove caps, re-lubricate all bearing surfaces with assembly lubricant, and install caps in correct positions. Install new main bearing cap bolts if provided in bearing set. Starting with center main (3), then front and rear (1 and 5), then intermediate mains (2 and 4), torque main cap bolts to specification in 3 progressive steps: first to 30 ft-lb, then 50 ft-lb, then final torque.
19. 19

    Check crankshaft endplay
    Using feeler gauge, check crankshaft endplay at thrust bearing (rear main, position 5). Insert feeler gauge between crankshaft thrust surface and thrust bearing flange. Pry crankshaft fully forward, then measure gap at rear. Then pry crankshaft fully rearward and measure gap at front. Specification for 327 endplay is 0.002-0.006 inch. If endplay is excessive, thrust bearing is worn or incorrectly installed. If endplay is too tight, thrust bearing surfaces may be damaged or bearing is incorrect size.
20. 20

    Verify crankshaft rotation
    Using crankshaft turning socket on front snout or harmonic balancer bolt, rotate crankshaft through 2 complete revolutions. Crankshaft should rotate smoothly with consistent resistance. Any binding, tight spots, or irregular resistance indicates problem with bearing installation, clearance, or alignment. If binding occurs, stop immediately and diagnose cause before proceeding.
21. 21

    Install rear main seal
    Install rope-style rear main seal in block and rear main cap grooves. On 1966 327, rear seal is 2-piece braided rope design. Cut seal sections to correct length allowing approximately 0.010 inch excess on each end. Coat seal lightly with oil. Press upper seal section into block groove using seal installation tool or wooden dowel, starting at center and working outward. Seal should protrude slightly above parting line. Install lower seal in rear main cap groove in same manner. After cap is installed and torqued, trim excess seal flush with block surface using sharp razor blade. Apply small bead of RTV at seal parting line on each side of rear main cap.
22. 22

    Reinstall piston and rod assemblies
    Clean piston ring grooves and inspect pistons for damage. Install rod bearings in rods and caps with assembly lube. Install piston ring compressor on piston 1. Orient piston with valve reliefs toward intake side (if directional). Apply oil to cylinder wall 1. Insert rod bearing end into cylinder first, guiding rod bolts with rubber hose protectors. Gently tap piston crown with hammer handle to compress rings and drive piston into bore. Guide rod onto journal 1 and install rod cap in correct orientation. Install new rod bolts if provided and torque to specification. Repeat for all 8 cylinders, verifying each rod cap matches its rod and orientation is correct. After all rods are installed, verify crankshaft still rotates freely.
23. 23

    Install oil pump and pickup
    Install oil pump driveshaft into block (shaft should engage cam gear and drop into position). Install oil pump with new gasket, aligning pump slot with driveshaft tang. Install pump retaining bolt. Install oil pump pickup tube with new gasket or O-ring and torque pickup tube mounting bolts. Verify pickup tube is positioned correctly (approximately 0.25 to 0.375 inch from bottom of oil pan) and not contacting pan.
24. 24

    Install oil pan
    Clean oil pan thoroughly and inspect for dents or damage that could reduce clearance. Install new oil pan gaskets on block (one-piece gasket or side gaskets with cork end seals). Apply thin bead of RTV silicone at front and rear block corners where cork seals meet side gaskets. Position oil pan and install bolts. Tighten oil pan bolts in cross pattern starting at center and working outward to avoid distorting pan. Torque oil pan bolts to specification (typically 10-12 ft-lb for small block Chevy).
25. 25

    Install timing set and front cover
    Install camshaft sprocket and crankshaft sprocket with timing chain, ensuring timing marks (dots or lines) are aligned at 6 o'clock position facing each other. Install camshaft sprocket bolts and torque to specification (approximately 18-20 ft-lb — verify against service manual). Apply assembly lube to timing chain. Install new timing cover gasket and seal. Position timing cover, ensuring cover seal properly engages crankshaft. Install timing cover bolts and torque to specification. Install harmonic balancer using installation tool (do not hammer onto crankshaft). Install balancer bolt and torque to specification.
26. 26

    Reinstall remaining engine components on stand
    Install distributor in original position (aligning marks made during disassembly). Install intake manifold with new gaskets, applying RTV at front and rear block corners. Torque intake manifold bolts to specification in proper sequence (inside-out, center to ends). Install exhaust manifolds with new gaskets. Install valve covers with new gaskets. Install water pump with new gasket. Install external accessories (alternator, power steering pump, fuel pump, etc.).
27. 27

    Remove engine from stand and reinstall in vehicle
    Remove engine from engine stand. Attach engine hoist and chains to lifting points. Carefully position engine into vehicle engine bay, aligning with transmission bellhousing. Use load leveler to adjust angle as needed. Guide engine onto motor mounts. Install motor mount bolts and torque to specification. Reconnect transmission to engine, installing bellhousing bolts and torque converter bolts if automatic. Remove engine hoist. Reconnect all accessories, wiring, vacuum lines, fuel lines, throttle linkage, exhaust system, and cooling system hoses in reverse order of removal.
28. 28

    Install new oil filter and fill engine with oil
    Install new oil filter after applying thin film of oil to filter gasket. Fill engine with 5 quarts of 10W-30 conventional engine oil (adjust quantity if filter and cooler lines were drained). Do not start engine yet.
29. 29

    Prime oil system
    Remove distributor and use oil pump priming tool (long shaft that engages oil pump driveshaft) connected to electric drill. Rotate priming tool with drill at moderate speed until oil pressure registers on gauge or oil appears at rocker arms (valve covers off). This ensures all bearings receive oil before initial startup. Reinstall distributor in correct position and orientation.
30. 30

    Fill cooling system and perform initial startup
    Fill cooling system with conventional ethylene glycol (green) coolant in a 50/50 mix with distilled water (approximately equal capacity to original system). Reconnect battery negative cable. Verify all connections are secure and no tools remain in engine bay. Start engine and immediately check for oil pressure (should register within 5-10 seconds). Allow engine to idle and monitor for leaks, unusual noises, or issues. Engine may run rough initially until timing is adjusted and air is purged from hydraulic lifters. Check and adjust ignition timing to specification. Allow engine to reach operating temperature while monitoring for leaks and proper cooling system operation.

Reassembly

1. Reinstall hood using alignment marks made during removal
2. Check all fluid levels (engine oil, coolant, transmission, power steering, brake fluid) and top off as needed
3. Bleed cooling system of air by running engine with radiator cap off until thermostat opens, then top off and install cap
4. Perform test drive and monitor oil pressure, engine temperature, and listen for unusual noises
5. After first 500 miles, change engine oil and filter (break-in period), then recheck main bearing cap bolt torque after engine is cold
6. Monitor oil consumption and pressure for first 1000 miles to ensure proper bearing break-in

Verification

• Oil pressure should read minimum 10 psi at idle when hot, 30-40 psi at 2000 RPM or higher depending on oil pump and bearing clearances
• Engine should run smoothly with no metallic knocking, ticking, or bearing noise
• No oil leaks from oil pan, timing cover, rear main seal, or any gasket surfaces
• Crankshaft should rotate freely by hand with spark plugs removed (before initial start)
• All main bearing clearances verified to be within 0.0008-0.0020 inch specification using Plastigage
• Crankshaft endplay verified to be within 0.002-0.006 inch specification
• Engine operates at normal temperature (160-195°F depending on thermostat) with no overheating

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