But if the engine needs to come apart for any reason, the chain guide wear surfaces should be checked. Modern applications should go well beyond 100,000 miles. There’s not much to do with respect to inspecting a timing chain. The job can cost well over $300, more or less in the same realm as a timing chain.” A timing belt is considered an internal engine component, mission critical and most manufacturers offer powertrain warranties of 100,000 miles and they do not want a mission critical component that can’t make it through the warranty period. “The Achilles heel of belts has always been the recommended change interval, which, for the most part, remains around 60,000 miles. However, according to another leading timing component supplier, over the past 20 years belt applications have been fading out. This makes rebuilds of chained OHC engines very expensive. Replacement chain kits can cost hundreds more than replacement belts, especially on OHC engines. They do make more noise, have higher weight and higher cost. Timing chains, with their thinner width, reduce overall engine length and are more durable, requiring no scheduled maintenance. They also require replacement, typically at 50,000 to 90,000 miles, depending on the belt’s construction. Belted engines need more room under hood. They are wider than chains, however, increasing the overall engine length. According to an aftermarket supplier of engine components belts offer lower weight, lower cost and less noise. Certain domestic engines from GM, Ford and Chrysler have the same design, but whether it’s interference or not, a timing belt or chain that breaks, stretches or is otherwise damaged is never a good thing.īoth belts and chains have advantages and disadvantages in each application. Interference engines can be found in some Acura, Honda, Hyundai, Infiniti, Isuzu, Nissan and Porsche applications, as well as some Audi, BMW, Mazda, Mitsubishi and VW applications. A cam drive failure can also cause expensive valve damage in “interference” engines that don’t have enough clearance to prevent the valves from hitting the pistons if the cam stops turning or jumps out of time. If a timing belt or chain breaks, or the cam drive gears fail, the cam stops turning, the engine loses all compression and the engine stops running.
Valve timing affects fuel economy, emissions and engine performance and, as with every other part of the engine, can only be properly maintained through a precise relationship between many different parts. The drive ratio is two to one, so at 3,000 rpm the cam is turning at 1,500 rpm.” That is why cams have big gears on the end and crankshafts have little gears. In a four-stroke engine, the intake and exhaust valves open and close every other revolution of the crankshaft, so the cam only turns at half engine speed. At 5,000 rpm it is about two hundredths of a second. At idle, the time interval between valve openings for each cylinder is about a fifth of a second. “Opening and closing the intake and exhaust valves in precise synchronization with the up and down strokes of the pistons requires very accurate timing. How important is accurate engine timing? According to Engine Builder Technical Editor Larry Carley, things that happen faster than the blink of an eye are critical. You CAN control the timing in an engine and here are some basics with regard to the differences and distinctions between timing belts and chains in the aftermarket. Timing is everything and being off even the slightest amount can have damaging, even disastrous effects. Under the hood, however, it’s a different story. If your timing is off, well, you’ll just have to live with the consequences, good or bad. Try as you might, though, you can’t do a lot to control events and situations. Even without realizing it, your personal timing has played a huge role in your and others’ life.
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