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
As for a more practical answer, I would have to say to hit government emissions regulations most manufacturers are using variable camshaft timing, in the form of an oil pressure driven gear on the end of the camshaft
My car had a chain. Still needs to be replaced. And costs more to do so. Maybe a slight benefit.
Chains are an overall better option but come with some significant drawbacks. Belts may not be as reliable, but they’re cheap and easy to replace because they’re accessible on the outside of the engine and only a few covers have to be removed to get to them. Timing chains are more reliable but they don’t last forever, and accessing them requires partial dissasembly of the engine which is more time consuming and more expensive. In both cases the failure of the chain or belt leads to catastrophic failure of the engine itself. Belts made sense because diagnosing a worn belt is easy and changing it is much cheaper and easier, so this creates a benefit for the owner where it’s making one of the most crucial service items cheaper and harder to ignore. But as technology has progressed chains have reached great levels of reliability and longevity and lubrication and tensioning systems are also far more effective and reliable themselves, which used to be a weak point in many engines for decades. At this point a timing chain can last long enough that when the time for it to be replaced comes, the cost of this replacement is overall cheaper than the cumulative amount spent on belt replacements will have been for the same time period.
It’s also worth noting that motorcycles have almost exclusively used chains in the majority of models for decades now, with only a few, notably Ducati, sticking to belts, which in turn has led to the constant development and refinement of timing chains.
Excellent examples of chain driven motors are:
Any pushrod design. 1 short chain. Pushrods get bent, new pushrods go in.
Inline single overhead cam motors without variable timing. 1 longer chain but still very simple.
Passable chain configuration:
V motors with single overhead cam. Two chains but nothing crazy.
Examples of bad chain driven motors:
V motors with dual overhead cams. Bunch of chains and tensioners, complicated but they could go the distance.
V motors with with dual overhead cams and variable valve timing. The phasers will be fucked up and the chains stretched at 100k.
V motors with dohc, vvt, and why in the fuck would you put chain on the back of the motor Audi? Well why not double down and make it a hot V with the starter in the valley?
I had a 2014 Ford Escape that required its “routine” timing belt replacement. The DOHC gears required a special piece to hold them in place, along with a special bolt to keep the crank at top dead center or else the timing was very difficult to get back correct. One bad movement and valves were banging into pistons. Oh, and the water pump was connected to the same belt, and was recommended to be replaced at the same time. Dealer wanted nearly USD $2k to do, because it was something like 17 hours (by the book) of labor. I found a reputable independent repair shop that did it for USD $1k.
Then the turbo went out and was quoted $2700 to replace. I sold it as is. I swear I will never intentionally purchase a vehicle with a timing belt. And hopefully no turbo.
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