The old Corollas in the 70s and 80s had timing chains. In the 90s, Honda, Toyota, and even Nissan started making belt-driven cranks instead of chains. Now they are back to timing chains. What happened?
In: Engineering
60k mile timing belt change intervals. They tried to stretch them to 80 and 100k miles, but that’s just tempting fate. The belts are cheap and quiet, but when they break the motor is toast. Chains are noisy and will ultimately stretch and get noisy and shift timing so the motor isn’t as efficient, but they rarely break and wreck the motor.
Chains are superior to belts in many ways (longevity, efficiency etc.) but early cam-chain engines lacked refinements like proper tensioning systems which led to high development costs and some catastrophic failures causing repetitional damage.
This led to a re-adoption of the well-known and tried-and-tested belt.
More recently, engine designers have re-embraced chains owing to better materials and tensioning systems making them cost effective and less likely to fail.
Belts are still chosen for some applications like race engines (where gear-driven cams are not present) because or their lightweight nature.
A big problem with chain timing belts is that over time the pins starts to wear out causing the chain to stretch and the engine to get out of time. Timing belts use strong nylon fibers to prevent this from happening. Even as they wear out they do not stretch. Eventually they will end up jumping teeth but they will have better timing before this happens, and you can just make sure to replace the timing belt before this happens.
There are a few things which have happened to make timing chains popular again. Firstly engines have become more powerful so there are more forces required to open the valves. Timing belts are usually not strong enough to handle this increase in power. And secondly we have made huge advancements in metallurgy and metallurgical processes which means we can now make metals that wear much slower. So the timing chains we make today last several times longer then those we made in the 90s.
TBH there’s not really that much of a trend, both have benefits and both are still commonplace. It’s more that specific engines use one or the other and sometimes, one specific engine model or architecture becomes incredibly commonplace. Like, for a while Ford stuck Duratec engines into damn nearly everything and some of those cars were among the most common in the world. So that one engine means “lots of cars have chains”.
There’s definitely been a backlash against wet belts though.
People complained about the costs of regularly scheduled timing belt service and the catastrophic effects of being ignorant to it. Manufacturers turned to timing chains to allay those fears and reduce ownership costs.
Another reason we have gone back to chains is that cars have more complex valve gear than they used to- variable valve timing systems may be more suited to chains than belts sometimes. Often these systems operate off of oil pressure so it can be difficult to keep the oil and belt separate. Chains prefer to be in an oil bath, belts not so much.
The move to timing belts was a cost saving measure. But timing belts are more prone to catastrophic failure which in most engines will lead to irreparable damage.
Timing chains are generally more durable than timing belts, which is why car manufacturers have shifted back to using them in recent years. Belts can wear down and break more easily, whereas chains can last the lifetime of the engine with proper maintenance.
It’s all in the actual engineering and execution but chains are generally more reliable and cheaper to maintain. Belts are cheaper engineering. The engines are easier to design and manufacture but more work for the customer. There’s fewer oil passages on the gear drive side of the engine in belt designs but they leak just the same. Glad Honda went to chains mostly years ago. Even Ferrari dumped belts on their V8 from the 430 and their V12 from the Enzo and 599.
Theoretically, belts need to be replaced more frequently. My 2012 Jetta TDI (which is the only belt driven timing system I’ve ever owned) called for a belt replacement every 110,000 miles if memory serves correct. My 2013 GMC Sierra has a timing chain that will last the life of the vehicle per GM guides which GM builds for trucks around a 1/4 million mile service life. Modern chains just to stretch like older chains did and tend to outlast modern belts.
Now timing gears….now we are talking. They will last the life of the engine (which in those applications may outlast several vehicles).
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