If the chain is quiet when the ICE is running, the chain is fine. They make noise before causing any problems. JeffD
I guess I was not clear enough, so... can I throw my timing light away? or is it still possible to check the timing ignition. I fin all get curious after 95000 miles ????
The timing light is not going to help you evaluate the timing chain. The timing chain governs the relationship between the crankshaft and the two camshafts. The ignition timing is based upon the crankshaft position and the engine ECU's determination of the appropriate spark advance/retard based upon engine temperature, accelerator pedal position, etc. Since the ignition timing is not affected by camshaft position, a loose timing chain will not affect ignition timing and consequently will not affect the timing light. As Jeff pointed out, unusual timing chain noise is the normal way to evaluate whether the timing chain is worn. I have a Craftsman timing light that requires connection to the cyl 1 high voltage wire. Since modern cars typically have individual coil on spark plug ignition, my timing light is obsolete. Unless I buy a classic vehicle in the future, the light will continue to gather dust in my garage. If you have a timing light with inductive pickup which will work with modern vehicles, then you can check the Prius engine ignition timing but it won't do you much good because you can't adjust the timing.
I've never heard of a chain tensioner "failing". The bearings may get noisy (squealing) and, maybe, loose (rattling) but I've never heard of anything else.
I was checking my valve clearances last weekend (will post info later) and noticed my timing chain had a lot of slack. I could push down on the chain between the two camshafts almost 1/2 inch with just finger pressure. It did spring back some when released. I googled for deflection tolerances for the timing chain but could not find any information. Is this normal? Car has around 250k, with no unusual engine sounds, runs fine.
Unlike a timing belt, the "tensioner" is not under high tension. It is more like a guide than an tensioner. They will be a lot of play on the "trailing" links of the chain. It would be wear on the gear or "stretch" when the timing ger on the canshaft is pulled by the chain that would change the original timing of the canshaft, which controls the opening and closing of the valves. All metals "stretch" under tension. It's not much. The other factor is wear one the bearing surfaces of the links. if you change the oil regularly, that should not be a problem.
