For this procedure, one needs the Volvo camshaft locking tool 999 5452, which stops the camshafts turning while the sprockets are removed, and details for a home-made alternative are given. It is important that the camshafts be locked so that valve timing is not lost. In addition it is necessary Volvo tool 999 5451. Start by removing the timing belt then remove the air cleaner assembly and intake ducts to get access to the left-hand end of both camshafts. Remove the cross-stay mounting bracket from the top of the engine, then for non-turk models remove the camshaft position sensor housing from the intake camshaft. For turbo models, eliminate the sensor housing from the exhaust camshaft and the sensor rotor plate. Next follow the instructions to remove the bracket from the cylinder head at the left hand end if fitted, and use a screwdriver to prime out the plastic blanking plug at the end of the appropriate camshaft, being prepared for oil spillage. Make sure that the slots in the camshafts are parallel to the join between the upper and lower parts of the cylinder head before locking them in place. Check the timing marks on the crankshaft sprockets and then fit the locking tool on the left-hand side of the cylinder head in such a way that it makes a firm contact with the camshaft slots. If both camshaft sprockets are going to be removed, mark them for identification. For a sprocket that has a variable valve timing unit, use a Torx 55 key to remove the plug and central retaining screw, then pull the camshaft sprocket off. For a sprocket that has no variable valve timing, remove the three bolts and pull out the sprocket. Carefully remove the seal without damaging the sealing face of the shaft, clean the seat of the seal, and lubricate the new oil seal, and fit the oil seal. Refit the camshaft sprocket with aligned timing marks, the bolts tightened just enough to permit movement. For the variable valve timing sprocket, make sure to place the crankshaft in the right position, remove the starter motor and insert the crankshaft stop tool. Rotate the crankshaft anti-clockwise until it hits the tool and press it with the VVT unit onto the camshaft and tighten the tight screw lightly. Adjust the sprocket bolts to the middle of the slots on the VVT unit and tighten gently and turn the VVT unit clockwise to stop and slacken the retaining screw. Temporarily reattaching the timing belt cover and aligning the marks in the sprocket rim with the timing belt cover then tighten the VVT unit screw to the specified torque. Fit the new timing belt to the sprockets, slacken off the bolts holding the VVT unit and non-WT sprocket and refit the center plug to the VVT unit, and tighten it to the specified torque. Apply the appropriate torque of the camshaft sprocket bolts and check the position of the timing belt tensioner arm and adjust, if needed. Finally, remove the camshaft locking tools and crankshaft stop tool, turn the crankshaft clockwise through two full revolutions and check that all the timing marks can be realigned, this means that the tensioner pointer is aligned with the central notch, then complete the refitting process.