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No. 21739
ID: dc700d
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, CAT C15 OHC timing gear layout.png
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>>21737
Gear drive is actually pretty common on pushrod engines, and diesels.
But chains and belts are generally used on OHC engines due to cost, simplicity, noise, and weight.
A timing belt is almost silent, and uses a minimum of components. The sprockets can be made of sintered iron, or stamped out of sheet metal. Idler bearings are literally just a bearing, with the belt riding directly on the outer race of the bearing. The entire system weighs a couple pounds.
The tradeoff is that they only last 50-70,000 miles.
Chains? A little louder, and a little more expensive, but not by much. They use about the same number of components as a belt but generally not idler bearings, instead using slipper shoes like in that Audi engine. Similar complexity to a belt (in a normal engine, not that Audi monstrosity). Again, the system is light.
Actually, most Big 3 V8s and some Big 3 OHV inlines use a chain rather than gears. Those systems are literally 2 sprockets and the chain.
Running an overhead cam engine on a gear train, that gets expensive and complex. Here's an OHC Caterpillar gear train. Detroits are similar. Even though they're helical gears, they're still noisier than a chain. Not noticeable on a diesel really but you'd hear it on a gas engine.
Think of the cost of machining each gear out, and pressing a bearing in to each one, instead of stamping out a sprocket (wham, done, next!)
Think of the weight of each idler gear needed to transmit the power (and how there would be twice as many on a V engine)
They're actually not that bad to time up though. Easier than a belt I would say.
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