How to Align the Timing Chain of the 4RB2 Engine?
3 Answers
After removing the cylinder head, sequentially remove the fan belt, slide rail assembly, damping plate assembly, and crankshaft timing sprocket. Straighten the chain, measure at 3 to 4 selected positions, and replace the chain if necessary. The minimum value for the intake camshaft timing sprocket is 113.8mm. Inspect the slide rail assembly and damping plate assembly; replace them if the maximum wear exceeds 1mm.
I've been repairing engines for over a decade, and there are several critical points to pay special attention to when aligning the timing chain on a 4RB2 engine. First, remove the timing cover and locate the crankshaft position mark, then rotate it clockwise to the top dead center of cylinder 1. Next, check the mark on the camshaft sprocket, which should align with the engraved line on the cylinder head. The timing chain usually has three differently colored links—the brightest one should align with the crankshaft gear mark, while the other two align with the marks on the two camshaft gears. Proper chain tension is crucial; it shouldn't be too tight. After installing the tensioner, manually rotate the crankshaft two full turns and recheck the alignment of all marks. Never skip this step—being off by even one tooth can cause anything from rough idling to pistons hitting valves. I've seen several engines sent for major repairs because people skipped the recheck to save time. Using a professional torque wrench to tighten the bolts is also essential, as a loose chain will produce noticeable noise. The entire process takes about three hours.
I've personally modified a 4RB2 engine, and timing chain alignment requires both courage and precision. First, remove the spark plugs to make it easier to rotate the crankshaft, then use a wrench to align the pulley mark with the cylinder block's reference line. On the camshaft side, use a specialized locking tool to secure the gear position and prevent rebound. The colored chain links must align precisely with the marked points on the sprockets—being off by half a tooth can cause issues. The most critical step is after installing the tensioner: slowly rotate the crankshaft two full turns and recheck the alignment—this step determines success or failure. The first time I did this, I lacked experience and immediately installed the cover, resulting in ignition problems. I recommend preparing a new chain and tensioner, as a stretched old chain won't allow precise positioning. The entire operation requires patience—don't interrupt midway, or the alignment may shift. After completion, test for at least 30 minutes to listen for any abnormal noises.
