Timing Chain Tensioner

This procedure replaces the timing chain tensioner on a 1966 Chevrolet Corvette 327ci V8, requiring partial timing cover access and precise torque specifications to ensure proper chain tension and engine timing integrity.

Warnings

Tools required

Parts

• Timing chain tensioner assembly × 1 — Use OEM specification
• Timing cover gasket set × 1 — Use OEM specification
• Timing cover access plug gasket/O-ring × 1 — Use OEM specification
• Harmonic balancer bolt × 1 — Use OEM specification
• Engine oil × 1 — 5W-30 Conventional
• Oil filter × 1 — Use OEM specification
• RTV silicone sealant (high-temp) × 1 — Permatex 81160 or equivalent

Fluids

• 5W-30 Conventional engine oil — 5 qt

Preparation

1. Park vehicle on level surface and engage parking brake.
2. Disconnect negative battery cable to prevent accidental starter engagement.
3. Allow engine to cool completely (minimum 2 hours after last operation).
4. Drain engine oil into appropriate container and remove oil filter.
5. Remove radiator upper hose from water pump to provide clearance.
6. Remove fan shroud bolts (if equipped) and position shroud away from fan.
7. Remove cooling fan and fan clutch assembly (4 bolts on water pump hub).
8. Remove drive belts from crankshaft pulley (alternator, power steering, air conditioning if equipped).
9. Mark distributor position relative to intake manifold for reference during reassembly.

Procedure

1. 1

   Remove harmonic balancer center bolt
   Using a breaker bar and crankshaft socket, remove the harmonic balancer center bolt. This bolt is torqued to approximately 60 lb-ft and may require significant force. Have an assistant hold the crankshaft from rotating by placing the transmission in gear (manual) or using a flywheel holding tool. Remove the bolt completely and retain the washer.
2. 2

   Remove harmonic balancer
   Install a harmonic balancer puller onto the balancer hub. Ensure the puller jaws grip the outer edge of the balancer, not the rubber damper ring. Tighten the puller center bolt gradually and evenly until the balancer releases from the crankshaft snout. Do not strike the balancer or use excessive heat, as this will damage the rubber damper element. Remove the balancer and inspect the crankshaft snout for damage or excessive oil leakage from the front seal.
3. 3

   Remove timing cover access bolts
   Locate the timing cover access area where the tensioner is housed. Remove the 3 bolts securing the timing cover access plate or inspection cover. These are smaller bolts that allow partial access to the timing chain tensioner without complete timing cover removal. Clean the area around the access opening to prevent debris from entering the timing case.
   Torque spec

   Timing Cover Access Bolts12 Nm (9 lb-ft)
4. 4

   Remove tensioner cap or plug
   Using the appropriate socket, carefully remove the tensioner cap or plug from the timing cover. This component may be under spring pressure from the tensioner mechanism. Control the plug as it releases to prevent the internal spring from ejecting suddenly. Remove and discard the crush washer or O-ring seal. Inspect the threads in the timing cover for damage.
   Torque spec

   Tensioner Cap/Plug30 Nm (22 lb-ft)
5. 5

   Remove tensioner housing bolts
   Remove the 2 tensioner housing bolts securing the tensioner assembly to the timing cover. These bolts must be removed carefully to avoid dropping them into the timing case. Note the bolt length and position for reassembly. If the tensioner uses a guide pin or locating dowel, note its position before removal.
   Torque spec

   Tensioner Housing Bolts25 Nm (18 lb-ft)
6. 6

   Extract old tensioner assembly
   Carefully withdraw the tensioner assembly from the timing cover. The tensioner may consist of a spring-loaded plunger or a pivoting arm with a rubber-backed guide pad, depending on production specifications. Inspect the tensioner face for wear patterns, grooves, or rubber deterioration. Inspect the timing chain visible through the access opening for wear, stretch, or damaged links. If chain wear is evident, note this for future repair planning.
7. 7

   Clean tensioner mounting surfaces
   Using a scraper and degreaser, thoroughly clean the tensioner mounting surface on the timing cover. Remove all old gasket material, RTV sealant, and oil residue. Clean the timing cover access bolt holes and ensure no debris or old gasket material remains. Wipe the area clean with a lint-free rag and allow solvents to evaporate completely before proceeding.
8. 8

   Prepare new tensioner assembly
   Unpack the new tensioner assembly and verify it matches the original design (spring-loaded plunger or pivoting guide). If the tensioner includes a locking pin or shipping pin to retain the spring in the compressed position, do not remove it yet. Apply a thin film of clean engine oil to the tensioner plunger or guide face to provide initial lubrication.
9. 9

   Install new tensioner assembly
   Carefully insert the new tensioner assembly into the timing cover opening, aligning the bolt holes and any locating dowels. If equipped with a shipping pin, keep it installed during this step. Apply a small amount of RTV sealant to the tensioner housing mating surface if the design does not use a separate gasket. Hand-thread the 2 tensioner housing bolts to secure the assembly loosely.
   Torque spec

   Tensioner Housing Bolts25 Nm (18 lb-ft)
10. 10

    Torque tensioner housing bolts in sequence
    Tighten the tensioner housing bolts to 25.0 Nm (18.0 lb-ft) using the specified tightening sequence: tighten the lower bolt first, then the upper bolt. This sequence ensures even clamping force and prevents housing distortion. If the tensioner has a shipping pin or locking pin, remove it now to allow the tensioner to apply pressure to the timing chain.
    Torque spec

    Tensioner Housing Bolts25 Nm (18 lb-ft)
11. 11

    Install tensioner cap with new seal
    Install a new crush washer or O-ring onto the tensioner cap or plug. Insert the cap into the timing cover opening, ensuring it threads smoothly without cross-threading. Hand-tighten the cap until it seats against the crush washer, then torque to 30.0 Nm (22.0 lb-ft). Do not over-torque, as this can strip the aluminum timing cover threads.
    Torque spec

    Tensioner Cap/Plug30 Nm (22 lb-ft)
12. 12

    Reinstall timing cover access bolts
    Install the timing cover access plate or inspection cover with a new gasket or RTV sealant as appropriate. Thread the 3 access bolts hand-tight, then torque them to 12.0 Nm (9.0 lb-ft) in a crisscross pattern to ensure even gasket compression. Verify no oil seepage around the access cover edges.
    Torque spec

    Timing Cover Access Bolts12 Nm (9 lb-ft)
13. 13

    Reinstall harmonic balancer
    Clean the crankshaft snout and the inside bore of the harmonic balancer with degreaser to remove any oil or debris. Inspect the crankshaft keyway and balancer keyway for damage. Align the balancer keyway with the crankshaft key and slide the balancer onto the crankshaft snout by hand as far as it will go. Using a harmonic balancer installation tool (not a hammer), press the balancer fully onto the crankshaft until it seats against the timing gear. Install the center bolt with its washer and torque to the manufacturer's specification (approximately 60 lb-ft, though this should be verified with OEM documentation).
14. 14

    Reinstall drive system components
    Reinstall the fan and fan clutch assembly to the water pump hub using the 4 mounting bolts. Reinstall all drive belts (alternator, power steering, air conditioning) and adjust to proper tension. Reinstall the fan shroud (if equipped) and secure with bolts. Reconnect the radiator upper hose to the water pump.
15. 15

    Refill engine oil and reconnect battery
    Install a new oil filter and torque according to filter manufacturer specifications (typically hand-tight plus 3/4 turn). Refill the engine with 5.0 quarts of 5W-30 conventional engine oil. Reconnect the negative battery cable. Start the engine and verify oil pressure within 10 seconds. Allow the engine to idle and inspect for oil leaks around the timing cover, tensioner cap, and access cover areas. Check that no unusual noises are present from the timing chain area.

Reassembly

1. Verify all timing cover bolts and access plugs are torqued to specification to prevent oil leaks.
2. Double-check that the harmonic balancer is fully seated on the crankshaft snout and the center bolt is properly torqued.
3. Confirm drive belt tension is correct for all accessories to prevent premature belt or bearing failure.
4. Verify distributor position has not shifted during the procedure; adjust ignition timing if necessary using a timing light.
5. Allow engine to reach operating temperature and recheck oil level; add oil if necessary to reach full mark on dipstick.

Verification

• Start engine and listen for timing chain noise; there should be no rattling, slapping, or excessive noise from the timing cover area.
• Verify oil pressure gauge shows normal pressure (40-60 psi at operating RPM for a healthy 327 V8).
• Inspect all timing cover areas for oil leakage with engine at idle and at 2000 RPM.
• Using a timing light, verify ignition timing is within specification (typically 4-8 degrees BTDC at idle with vacuum advance disconnected for 1966 327 V8).
• Road test vehicle and verify smooth acceleration with no timing chain noise under load.
• After 50-100 miles of operation, recheck oil level and inspect timing cover area for delayed oil seepage.

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