networkn:

 

 

 

The whole reason chains were invented, was to lessen the problems from a belt. It's the reason for it's existence. 

 

 

Cambelts are a relative latecomer. They weren't common at all until advances in belt technology and the move to overhead cam engines made them viable.
But gears, chains, belts.. all are equally good engineering solutions for specific applications.

A lightweight OHC boxer engine with the cams far away from the crank lends itself to a light, quiet belt drive. They're mechanically leveraged (small drive pulley and large cam pulleys) to put less strain on the belt, and it's relatively easily replaced.

Heavier OHC V8's with cams also far from the crank often use long chains - stronger, but not always quiet, cheap or reliable.

If you need something that'll last forever in extreme use – you get a heavy, noisy gear drive as used on most industrial engines.
We used to build (pushrod) V8 engines, usually chucking the factory timing chain, and replacing it with a gear drive that would last with high revs, high lift cams, and high pressure valve springs.

There's going to be a tradeoff between longevity, noise, weight, and servicability - in climatic extremes, or at the outer limits of the engine's design envelope - balanced against customer expectations. The 'best' engineering solution is often not the one used. Cost looms large in manufacturer's choice of cam drive system. Ease of replacement is somewhere down the list – as that often falls to a 2nd or maybe 3rd owner.

I've just reinstalled the timing chains on my 2013 SOHC 6.2 Ford – at 80K! – after the oil pressure activated tensioning system gave up. And recently replaced my wife's Subie belt at 140K which (with obligatory tensioners waterpump, oil & cam seals) cost about the same.

I have a theory those manufacturer recommended replacement intervals are very conservative. But my wife disagreed and wouldn't let it go any longer.

A friend and I've bought Subies for years as fix-up projects. Many have clearly NEVER had the original cambelt replaced. One barely running car we got recently with 190,000km turned out to have the original factory plugs in it – the electrodes had completely eroded away - incredibly it still ran. The factory belt still looked OK -with a little crazing. The few with belt failures we've bought all had K's in the mid or high 200's (they'd failed by stripping a tooth or idler failure rather than a snapped belt) and those were likely their original belts.

It'll all be moot soon anyway.
There's growing use of electronically driven valvetrains, and in the more distant future the internal combustion engine will likely be consigned to history as steam engines are today.