Like timing belts, timing chains drive a vehicle's camshaft. Stronger than their counterparts, timing chains are nearly repair-free with no definitive replacement schedule. If your Ford Taurus produces a vociferous rattle whenever you accelerate, chances are it's time to check and replace your timing chain. Here's how that's done in a Taurus with a 3.4L DOHC engine.
Check your owner's manual for the recommended mileage for replacing your timing chain. Replacement for a Ford Taurus is 100,000 miles.
Locate the timing chain. Replace it if the automatic chain adjuster (also known as the tensioner) is damaged or worn.
Take off the engine front cover and the crankshaft position sensor pulse ring
Position the crankshaft so the No. 1 piston is at "Top Dead Center" (TDC). The crankshaft key-way groove and the oil pump mark should line up.
Confirm that the camshaft sprockets line up on top. You may need to turn the crankshaft one full revolution and check again.
Disengage the timing chain guides, tensioner arm and tensioner retaining bolts and take the timing chain off the engine.
Discharge the tensioner ratchet/pawl mechanism via the tensioner's access opening. Place a small wire inside the piston's top to unseat the oil check ball. This compacts the tensioner rack and piston into the tensioner housing. Condense the tensioner manually.
Eliminate the camshaft timing chain sprockets if they are worn or damaged.
Turn the crankshaft so the No. 1 piston is at TDC. The crankshaft key-way groove and the oil pump mark should line up.
Line up the sprocket and chain timing marks and install the timing chain. The crankshaft, camshaft and balance shaft also should line up.
Reconnect the camshaft sprockets (if replacing). Secure the sprocket bolts at 48 to 70 foot pounds (64 to 95 Nm).
Put in the compressed timing chain guides, tensioner arm and tensioner. Secure the tensioner's pivot bolt at 25 to 39 foot pounds (34-53 Nm) and secure the retaining bolts at 14 to 20 foot pounds (18-27 Nm).
Align the timing chain's timing index marks and the crankshaft and camshaft sprocket and balance shaft driven gear index marks.
Connect the crankshaft position sensor pulse ring to the crankshaft. Line up the crankshaft key and the sensor ring's key-way.
Replace the engine front cover.
