Belts tend to fail abruptly and catastrophically, but generally only if they're neglected and used well beyond their design life. Chains fail more insidiously, because they get longer over time. The pins eat away at the plates, increasing the spacing between the rollers. This isn't immediately noticeable, because the timing sprockets will wear to match the altered dimensions of the chain. Worn chains cause all sorts of subtle timing problems and the lifespan of a chain is much less predictable, because it's highly dependent on lubrication; missed oil changes or poor oil quality will drastically accelerate chain wear.

From an enthusiast's perspective, a chain is probably preferable, because it tends to give you some warning before it fails - you might hear a rattle at idle, you might have problems with starting or misfires, you might get a check engine light and an EBD-II code from the timing sensors. That's a much less scary prospect than the potential for a sudden and catastrophic failure of a timing belt.

From a manufacturer or dealership's perspective, belts have some clear advantages. Unless there was a manufacturing defect in the belt, they'll almost never cause trouble if replaced according to schedule. That has obvious liability implications - it's not their fault if the customer ignores the specified replacement interval, but it potentially is their fault if a chain wears faster than expected. BMW, VAG and Jaguar Land Rover have all recently settled class action lawsuits related to the premature failure of timing chains.

I'm more of a hobby bicycle mechanic. Isn't there some similar tool for the meassuring of the chain as you get for bicycles? Just push it down and you directly see if it's time to change the chain. If not done early enough you have to change all the sprockets too because of wear. If done in time, you might not have to change all the sprockets.

You can measure it with an ordinary caliper, but the problem is getting access. The timing chain needs to be continuously supplied with oil, so it is in rather than on the engine and can rarely be accessed without pulling the engine from the car. It takes several hours just to access the chain for inspection, so it's not something you'd periodically check - if you suspect a timing chain problem, you might as well replace it.

VW had a few years making cars with chains that would catastrophically fail. Lots of destroyed engines. It was the EA888 put in Golf GTIs from 2010 and on. After like 5 or something revisions they finally improved the tensioner that caused the failure.

Previous gen GTI was a belt. Garage told me they preferred belts because people know they need to replace those. People aren't expecting to be told your chain needs to be replaced plus it's much more expensive and labour intensive.

Never heard of Honda having problems with chains, though. Some of their motorbikes even had gear driven cams! (VFR I think).

Can confirm, have a 2012 GTI, replaced the stretched chain on it about 10 days ago. The problem is that they provided no service interval for the timing chain when it really needs replacement every 80K miles. It’s an enthusiast car so there are a ton of aftermarket parts that are of good quality and VAG cars share so many parts (the 2.0T e888 engine is in a ton of vehicles from 2008 through today). My car has 211K and I intend to take it well over 300K.

Oh, the chains themselves can fail, in a quite a dramatic fashion, flying through your engine hood.. But that tends to happen well after the mileage they were designed for.

They are by no means immortal, but, by design, should have a much longer lifespan than belts.

> Virtually every engine I know with a chain ends up either regularly failing early [..]

But I have no idea which early-failing models OP is referring to, as the engines I know about where quite reliable. (As in 1e6+ km reliable, with chain maintenance per manufacturer guidelines.)