Main Bearings

Complete replacement of main bearings on a 1972 Ford F-100 302ci V8, requiring crankshaft removal and precision measurement for proper bearing selection and clearance verification.

Warnings

Tools required

Parts

• Main bearing set (standard or appropriate undersize) × 1 — Use OEM specification or Clevite MS-909P equivalent
• Thrust bearing set × 1 — Included in main bearing set or separate
• Rear main seal (rope or neoprene) × 1 — Use OEM specification
• Oil pan gasket × 1 — Fel-Pro OS30040 or equivalent
• Timing cover gasket × 1 — Use OEM specification
• Oil pump gasket × 1 — Use OEM specification
• Valve cover gaskets × 2 — Use OEM specification
• Intake manifold gasket set × 1 — Fel-Pro MS95027 or equivalent
• Exhaust manifold gaskets × 2 — Use OEM specification
• Main bearing cap bolts (if reusing shows any damage) × 1 — Use OEM specification
• Engine assembly lube × 1 — Use moly-based assembly lube
• RTV silicone sealant (high-temp) × 1 — Permatex 81160 or equivalent
• Oil filter × 1 — FL-1A or equivalent

Fluids

• 10W-30 or 10W-40 conventional engine oil — 5 qt
• Ethylene glycol green 50/50 coolant — 15 qt

Preparation

1. Park vehicle on level surface, engage parking brake, and place wheel chocks at all four wheels
2. Disconnect negative battery cable
3. Drain engine oil completely and remove oil filter
4. Drain cooling system completely at radiator petcock and block drain plugs
5. Remove hood and set aside on protected surface
6. Remove air cleaner assembly and carburetor linkage
7. Label and disconnect all vacuum lines, electrical connections, and fuel lines from engine
8. Remove radiator, fan shroud, fan, and water pump drive belt
9. Disconnect exhaust system at manifolds
10. If equipped with power steering or A/C, remove belts and set accessories aside without disconnecting hoses
11. Support transmission with floor jack and remove bellhousing bolts
12. Attach engine hoist to factory lifting points on intake manifold or cylinder heads
13. Remove engine mount through-bolts
14. Have clean workspace prepared for engine disassembly with engine stand ready

Procedure

1. 1

   Remove engine from vehicle
   Verify all connections are disconnected. Slowly lift engine while guiding away from transmission input shaft. Tilt engine slightly as needed to clear firewall and body components. Once clear of vehicle, lower onto engine stand and secure with 4 engine stand bolts threaded into bellhousing mounting holes. Ensure engine is securely mounted before releasing hoist.
2. 2

   Remove external components
   Remove valve covers, intake manifold with carburetor attached, exhaust manifolds, distributor (mark position before removal), fuel pump, water pump, harmonic balancer, timing cover, and timing chain/gears. Remove oil pan and oil pump assembly. Mark distributor drive gear orientation before removing.
3. 3

   Remove cylinder heads and inspect cylinders
   Remove all 10 head bolts from each cylinder head in reverse of tightening sequence (work from outside toward center). Lift heads off block. If cylinders show significant ridge at top, use ridge reamer to remove before attempting to remove pistons. Inspect cylinder walls for scoring, taper, and out-of-round condition.
   ℹ️Cylinder heads can be left installed if only replacing main bearings, but removal provides better access and cleaning opportunity.
4. 4

   Remove rod caps and mark components
   Mark each connecting rod and cap with cylinder number (1-8) using number stamps on the side opposite camshaft. Rod caps are not interchangeable between cylinders. Remove the 2 rod cap bolts from each rod and lift off cap with bearing. Push piston/rod assembly up into cylinder bore. Install rod caps back onto rods loosely to keep matched sets together. Store assemblies in order.
   ⚠Connecting rods and caps must remain matched sets. Never mix caps between rods.
5. 5

   Mark and remove main bearing caps
   Main bearing caps are numbered 1-5 from front to rear and have directional arrows or offset positioning. Verify existing markings are legible or create new marks. Number 3 main bearing (center) contains the thrust bearing surfaces. Remove the 2 bolts from each main cap working from front to rear. Caps will be tight; use soft-face hammer or cap puller to break free. Do not pry against machined surfaces. Remove caps and bearing shells, keeping each cap with its bearing shell in order.
6. 6

   Remove crankshaft
   Remove upper bearing shells from block, noting the position of the thrust bearing halves at the number 3 main journal. Carefully lift crankshaft straight up and out of block. Crankshaft weighs approximately 50-60 lbs; use care to avoid dropping. Place crankshaft on clean padded surface or in suitable cradle. Remove rear main seal from block and rear cap.
7. 7

   Clean and inspect block bearing saddles
   Thoroughly clean all 5 main bearing saddles in block using clean shop rags and solvent. Remove all old oil, debris, and bearing material residue. Clean oil passages in block with rifle brushes or pipe cleaners. Blow out all passages with compressed air. Inspect bearing saddles for scoring, galling, or damage. Check for cracks around bearing saddles and main caps. Block must be completely clean and dry before measurements.
8. 8

   Measure crankshaft main journals
   Clean crankshaft journals thoroughly with solvent and dry completely. Using outside micrometer, measure each of the 5 main bearing journals at 4 points (90 degrees apart) and at 3 locations (front, center, rear of journal width). Standard diameter for 302 main journals is 2.2482-2.2490 inches. Record all measurements. Check for taper (difference between front and rear) and out-of-round (difference in diameter at different points). Maximum taper or out-of-round is .0005 inch. If journals are worn more than .001 inch undersize or show taper/out-of-round beyond spec, crankshaft must be reground and undersize bearings used.
9. 9

   Measure main bearing bore diameter
   Install all main bearing caps (without bearings) in correct positions and orientations. Torque cap bolts to 60-70 ft-lbs. Using telescoping bore gauge and outside micrometer, measure the inside diameter of each bearing bore at multiple points. Standard bore diameter should be consistent across all 5 mains. Out-of-round or misalignment indicates block line-boring may be needed. Record all measurements to compare against journal sizes for bearing clearance calculation.
10. 10

    Select and install upper main bearings
    Based on crankshaft journal measurements, select appropriate bearing size (standard, .010, .020, or .030 undersize). New bearings in standard size should provide .0005-.0015 inch oil clearance with standard journals. Remove main caps. Install upper bearing shells into block saddles, ensuring bearing tang engages slot in saddle. Upper thrust bearing halves install in number 3 position with thrust surface facing outward. Coat bearing surfaces with assembly lube. Do not get assembly lube on bearing backs or parting surfaces.
11. 11

    Install crankshaft and lower bearings
    Carefully lower crankshaft into block, seating journals into upper bearing shells. Install lower bearing shells into main caps with tangs engaged in slots. Install lower thrust bearing halves in number 3 cap with thrust surfaces facing outward. Coat lower bearings with assembly lube. Install main caps in correct positions (numbers 1-5, front to rear) with directional markings facing forward. Start all cap bolts finger-tight.
12. 12

    Check bearing clearance with Plastigage
    Before final torquing, verify bearing clearance using Plastigage. Remove each main cap one at a time. Place a strip of Plastigage across the full width of the crankshaft journal, parallel to crankshaft centerline. Reinstall cap and torque bolts to 60-70 ft-lbs. Do not rotate crankshaft with Plastigage installed. Remove cap and measure width of flattened Plastigage using scale on package. Clearance should be .0005-.0015 inch for all main bearings. If clearance is too tight or too loose, determine cause and correct before proceeding.
    ⚠Never rotate crankshaft with Plastigage installed or measurement will be invalid.
13. 13

    Set crankshaft endplay
    Remove Plastigage from all journals with clean rag. Apply fresh assembly lube to all bearings. Install all main caps in correct order and orientation. Torque all main cap bolts to 60-70 ft-lbs in two steps: first to 35 ft-lbs, then to final specification, working from center (cap 3) outward. Using pry bar or screwdriver, carefully pry crankshaft fully forward, then mount dial indicator against front of crankshaft snout. Zero indicator, then pry crankshaft fully rearward and read endplay. Specification is .004-.008 inch. If endplay is incorrect, thrust bearing size must be corrected.
    ℹ️Excessive endplay will cause thrust bearing failure. Insufficient endplay will cause thrust bearing to overheat and fail.
14. 14

    Install rear main seal
    302 Ford uses either rope-type or neoprene rear main seal depending on year. For rope seal: install upper seal half in block groove with both ends protruding slightly, then tap into place with seal installer or wooden dowel. Trim ends flush with block parting surface. Install lower seal half in rear main cap groove similarly and trim flush. For neoprene seal: carefully tap upper and lower seal halves into grooves using seal installer, ensuring lip faces forward (toward engine front). Apply small amount of RTV to seal end contact points.
15. 15

    Reinstall connecting rod assemblies
    Coat rod bearing surfaces with assembly lube. Install rod assemblies into cylinders from top of block, compressing rings if heads were removed. Guide rod bolts through rod journals with rubber hose over threads to protect journal surface. Install rod caps in correct orientation (match marks aligned) and torque rod cap bolts to 19-24 ft-lbs. Verify crankshaft rotates freely after each rod is installed. After all rods are installed, recheck crankshaft rotation; should turn smoothly by hand.

Reassembly

1. Install oil pump and prime oiling system using priming tool driven by electric drill until oil pressure is observed at all rocker arms
2. Install new oil pan gasket using small dabs of RTV at front and rear seal junctions, then install oil pan
3. Install timing chain and gears with timing marks aligned (camshaft mark at 6 o'clock, crankshaft mark at 12 o'clock)
4. Install timing cover with new gasket, harmonic balancer, and water pump
5. Install cylinder heads with new gaskets if removed, torquing head bolts to 65-72 ft-lbs in three steps following proper sequence (center out)
6. Adjust valves to .019 inch intake and .019 inch exhaust (hydraulic lifter initial setting)
7. Install intake and exhaust manifolds with new gaskets
8. Install distributor with rotor pointing to number 1 cylinder at TDC compression stroke
9. Install all remaining external components, belts, and accessories
10. Install engine in vehicle in reverse order of removal, reconnecting all mounts, transmission, exhaust, wiring, hoses, and linkages
11. Install new oil filter and fill engine with 5 quarts of specified oil
12. Refill cooling system with 15 quarts of 50/50 coolant mixture
13. Reconnect battery cable

Verification

• Before starting engine, rotate crankshaft 2 complete revolutions by hand to verify no binding or interference
• Verify oil pressure gauge or light is functional
• Start engine and immediately verify oil pressure registers (should be 40-60 psi at startup)
• Listen for any unusual knocking, ticking, or grinding noises that would indicate bearing problems
• Monitor oil pressure during first 20 minutes of operation; pressure should remain steady at 35-60 psi at operating temperature
• Check for oil leaks at pan gasket, timing cover, and rear main seal after engine reaches operating temperature
• Allow engine to idle for 20 minutes, varying speed occasionally, while monitoring temperature and oil pressure
• Perform 500-mile break-in with conventional oil before switching to normal service intervals

More procedures for this vehicle