K24 VTC Actuator Cold-Start Rattle: Diagnosis and Actuator Replacement (2009-2010 Acura TSX, 2008-2012 Honda Accord 2.4)
- The bulletins state they are for skilled technicians with the proper tools; if cam timing is wrong the valves and pistons can be damaged.
- Never use an impact wrench on the VTC actuator bolt.
- Support the car on a lift or jack stands before working underneath, and disconnect nothing electrical with the ignition on.
- Do not start the engine until the tensioner cover sealant has cured (Honda says 3 hours).
Introduction
A loud metallic rattle lasting about two seconds right after a cold start on a 2.4-litre K24 is the classic sign of a failing intake-cam VTC (variable valve timing control) actuator. Honda covered it in service bulletin 10-024 for the 2009 TSX and early 2010 TSX (up to VIN JH4CU2...AC027068) (https://static.nhtsa.gov/odi/tsbs/2012/SB-10037360-5339.pdf) and in bulletin 09-010 for the 2008-2012 Accord 4-cylinder and 2007-2012 CR-V (https://static.nhtsa.gov/odi/tsbs/2012/SB-10041669-6712.pdf). Honda's fix replaces the actuator without removing the whole cam chain: the auto-tensioner is pinned, the intake camshaft is lifted out with the actuator on it, and the actuator is swapped on the bench. The bulletins are written for trained technicians and warn against DIY attempts. This is an advanced job, and an error in cam timing can damage the engine. The first-generation TSX (CL9, K24A2) is not listed in these bulletins, so do not assume the parts or procedure carry over to it. Adapted from American Honda Motor Co. service bulletin 10-024, published by NHTSA (https://static.nhtsa.gov/odi/tsbs/2012/SB-10037360-5339.pdf).
Procedure
17 steps-
Step 1: Confirm the symptom
Let the car sit without starting for at least 6 hours so the oil drains out of the VTC system. Then start the engine and listen right away. A loud rattle from the engine for about 2 seconds that then stops matches the bulletin. If you hear a different noise, or nothing, diagnose further before buying parts.
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Step 2: Remove the top-side parts
Remove the strut (frame) brace if fitted and the engine cover. Remove the ignition coil cover and the four ignition coils. On reassembly the coil cover bolts are 9.8 N-m (7.2 lb-ft) and the coil bolts 12 N-m (8.8 lb-ft).
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Step 3: Remove the cylinder head cover
Pull the dipstick, disconnect the breather hose and the brake booster vacuum hose from the head cover, remove the two bolts holding the EVAP canister purge valve bracket to the head, then remove the cylinder head cover.
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Step 4: Get to the crank pulley and tensioner
Raise the car safely, turn the wheels or remove the right front wheel, and remove the splash shield so you can turn the crankshaft pulley. Remove the cam chain auto-tensioner (chain case) cover from the front of the engine.
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Step 5: Set TDC and pin the tensioner
Turn the crankshaft clockwise to top dead centre for No. 1 cylinder (white TDC mark). Then turn the crank slightly counterclockwise to compress the auto-tensioner, line up the hole in the lock with the hole in the tensioner and insert the 1.2mm (0.05 in) lock pin. Turn the crank clockwise back to TDC No. 1.
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Step 6: Mark the chain
Lower the car. Mark the timing chain where it meets the punch marks on the exhaust camshaft sprocket and on the VTC actuator, and wire-tie the chain to the exhaust sprocket so it cannot slip.
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Step 7: Remove the camshaft holders
Loosen the camshaft holder bolts in sequence, two turns at a time, so the cams are released evenly. Remove the five holders and lay them out in exactly the order and orientation they came off.
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Step 8: Lift out the intake camshaft and actuator
Lift the free end of the intake camshaft just far enough for a helper to ease the chain off the actuator's teeth. Take the camshaft out with the actuator still attached while the helper keeps slight tension on the chain, then hang the chain from the A/C compressor hose with a zip tie so it cannot drop into the timing cover. Lay the camshaft on a clean, padded bench.
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Step 9: Swap the actuator on the bench
Have the helper hold the camshaft still with an open-end wrench on its flats while you undo the actuator bolt and pull the old actuator off. Check that the new actuator is unlocked, push it onto the camshaft without forcing it, and turn it counterclockwise (looking at the actuator face) until it drops onto the camshaft's locating pin. Oil the bolt threads and run the bolt in by hand.
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Step 10: Unlock a locked actuator if needed
If the new actuator is locked once it is on the camshaft, seal oil port #1 on the camshaft with several wraps of electrical tape held by a zip tie, blow compressed air into port #2, and turn the actuator by hand until it unlocks. Afterwards remove all the tape and any adhesive left behind.
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Step 11: Torque the actuator bolt
With the camshaft held by the assistant, torque the actuator bolt to 113 N-m (83 lb-ft) with a hand torque wrench. Do not use an impact wrench; it can damage the actuator housing, vanes or lock pin. Then rotate the actuator back to the locked position.
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Step 12: Refit the intake camshaft
Take the chain off the A/C hose while the helper keeps it lightly tensioned. Feed the camshaft in at an angle so the chain sits over the actuator's teeth, and line up your paint marks with the punch marks on the exhaust sprocket and the actuator. Oil the journals and caps of both camshafts, then lower the intake camshaft into place.
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Step 13: Torque the camshaft holders
Fit the holders in their original positions. Tighten them two turns at a time, starting in the middle and working outward in the service-manual sequence, to 22 N-m (16 lb-ft) for the 8 x 1.25 mm bolts and 12 N-m (8.7 lb-ft) for the 6 x 1.0 mm bolts.
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Step 14: Release the tensioner and verify timing
Pull the lock pin out of the tensioner and cut the zip tie off the exhaust sprocket. Turn the crankshaft clockwise through two full turns and stop on the white TDC mark; both camshafts must line up as before. Look down inside the block to check that the chain is sitting on its guide and has not dropped behind it.
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Step 15: Reseal the tensioner cover
Clean off the old sealant, apply fresh Hondabond HT and reinstall the auto-tensioner cover, tightening its bolts to 12 N-m (8.7 lb-ft). Honda says to wait 30 minutes before adding oil and 3 hours before starting the engine so the sealant can cure.
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Step 16: Check valve clearance
With the head cover off, check and adjust the valve clearance cold: intake 0.21-0.25 mm (0.008-0.010 in), exhaust 0.25-0.29 mm (0.010-0.011 in). Tighten the locknuts to 14 N-m (10 lb-ft).
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Step 17: Reassemble
Refit the splash shield and wheel, then the cylinder head cover, tightening its bolts in three passes in sequence to a final 12 N-m (8.7 lb-ft). Reconnect the dipstick, breather hose and brake booster hose (bolts 12 N-m / 8.8 lb-ft), the purge valve bracket, coils, coil cover, engine cover and strut brace. Check the oil level, observe the sealant cure time, then start the engine and confirm the rattle is gone on the next cold start.
- Keep the camshaft holders in order; they are machined in place and must go back in the same positions.
- Paint marks on the chain are much easier to see than the factory punch marks once the chain is loose.
Related procedures
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