Timing chain and sprockets — inspection [Toyota Highlander XU20]

21. Visually inspect all components for wear and damage. Check the timing chain for loose roller axles, cracks, wear on rollers and side plates. Check the sprockets for hooked teeth, dents and broken teeth. Also check the timing chain for stretching and measure the diameter of the sprockets taking into account wear in the position when the chain is put on the sprockets. The stretching of the timing chain is measured by checking the length of the chain section limited by 8 links (16 roller axes) in three or more places (randomly selected) along the entire length of the chain. If the chain stretching on a section of 8 links exceeds the norm, the chain should be replaced (fig. 6.21, a). When checking the sprocket diameter, measure across the chain rollers, and measure chain elongation at three or more locations along the length of the chain. Maximum Chain Elongation and Minimum Sprocket Diameter (with a chain on) must not exceed the values specified in the Specifications at the beginning of this chapter (fig. 6.21, b). If the engine has high mileage or the inspection gives negative results, replace the timing chain complete with sprockets.

Fig. 6.21, a. The straightening of the timing chain is measured by checking the length of the chain section and 8 links (16 roller axes) and in three or more places not the entire length of the chain

Fig. 6.21, b. Wrap the chain around each sprocket and measure the sprocket diameter on the chain rollers. If the measurement result is less than the minimum allowable sprocket diameter, the chain and sprockets should be replaced

22. Check the guides for excessive wear (Fig. 6.22). Replace the chain guides if the wear exceeds the tolerances given in the Specifications at the beginning of this chapter. Note that some scratching of the timing chain guide is normal. If excessive wear is observed, you will also need to inspect the chain guide oil hole on the front of the cylinder block for blockage (fig. 14.5). The oil pump is driven by a second chain, which is driven by a sprocket on the crankshaft. If the timing chain must be replaced, replace the oil pump drive chain at the same time (see paragraph 14).