BMW 325is Timing Belt Replacement at your home or office.

How do mechanics replace the timing belt?

Engine designs vary, and thus the replacement procedure will vary, but broadly, the procedure is as follows:

• Disconnect the battery ground cable.
• Once the engine is cold, set the crankshaft to top dead center with the number one piston on the compression stroke. Remove crankshaft pulley.
• Remove all accessories interfering with the removal of the timing belt covers.
• Remove timing belt covers. Lock camshafts, as required, and note position of camshaft timing marks. Remove timing belt tensioner and idler pulleys. Remove timing belt.
• If replacing the water pump, do so at this time, and of course drain the cooling system first. If the engine cooling system thermostat is only accessible with water pump replacement, the thermostat should be replaced as well.
  
• Installation of the new timing belt includes all of the above steps, performed in reverse, following strict guidelines to assure camshaft and crankshaft (and balancing shaft, if equipped) are in perfect alignment after tensioner has been set.
• Upon completion of the installation, the engine crankshaft is turned by hand 720 degrees and the correct position of the timing marks on the crankshaft and the camshafts is confirmed.
  
• The vehicle is road tested to confirm normal operation and a service sticker is affixed to the engine noting the date of belt replacement and the vehicle mileage.