How to align the timing chain on a BMW 525?
3 Answers
Remove the intake and exhaust camshafts and place them on a flat surface, then install the chain. Both the intake and exhaust camshaft sprockets have grooves. Align the two grooves parallel to each other, then use a vernier caliper to pull both sides into alignment. After placing them on the cylinder head and aligning them, the camshaft grooves and the cylinder head screw holes should all be aligned, so you can tell when they are properly leveled.
I replaced the timing chain on my BMW 525 last year, let me share my hands-on experience. First, you must use special tools to lock the crankshaft position, rotate the crankshaft pulley to the top dead center of cylinder 1 - there's an inspection hole on the left side of the engine to confirm this. Then handle the camshafts; both camshafts have positioning holes at the rear that need to be secured with BMW's special tools to ensure they're horizontally fixed. When installing the new chain, pay special attention to the alignment marks - the yellow links on the chain must align precisely with the marks on the crankshaft gear and both intake/exhaust camshafts. The most critical step is manually rotating the engine two full revolutions to verify all marks realign, confirming no skipped teeth. The entire process works best with two people, especially during installation of the hydraulic tensioner which requires particularly delicate handling.
Having worked in an auto repair shop for over five years, I've handled BMW timing systems numerous times. For the 525's timing chain, the core lies in three steps: positioning the crankshaft, securing the camshafts, and aligning the marks. First, use a hex key to rotate the crankshaft to TDC (Top Dead Center) while immobilizing the flywheel to prevent rotation. Second, operate on the valve cover by inserting camshaft positioning tools into the slots at both camshaft ends to lock their phases. Third, when replacing the old chain with a new one, ensure the triangular marks on the intake and exhaust cam gears precisely align with specific chain links. Finally, remember to reset the locking pin before installing the hydraulic tensioner—this step is often overlooked, leading to insufficient tension and abnormal noises.
