Originally Posted by 123go

Shocking how people chance their timing belt/chain(s) to last past service recommendations.
I personally changed hundreds of belts/chains and 25yrs ago it was common to see a belt in rough shape at 60-80k inspection so you instantly realized its life was over.
Now days I rarely see belts looking worn out as they're made so much better now, well' China belts are trash and show wear, may even break at 50k. Buyer beware!
What I do see around replacement time or even past that time, are belts that are stretched and the tensioner totally seized (hydraulic) and/or spring tensioner just worn out but you cant tell this until you tear it all down.

This causes belts/chains to simply fall off pulleys. Being the p.o.c. we all know they are, my friend just towed his GM Aveo to the junk yard last summer.
First engine was destroyed around 65k miles on a trip out of state when its timing belt slipped off. A shop there put in a used 35k mile engine and the exact same thing happened again around 80k miles on the 2nd engine. Car was never driven hard, always maintained and no towing, all of which greatly shortens your belt/chain life.
It can happen to any car but my point is that's what I see more than anything.
Its not often a belt actually "breaks" since today's belts are as tough as chains, not seen one break within recommended intervals in several yrs. Ask a Harley rider what he puts his bikes belts through, Harley's ran belts instead of chains for many yrs now.

Timing belt driven water pumps tend to leak onto belts/pulleys making the belt slide off so beware when your antifreeze disappears. Toy/Lexus designed their pumps to not drip on belt/pulleys bad but older Toys did it. Most other car makes belt still get very wet and slide off so pay attention to your anti levels.
I've seen belts 50-75k miles past due still looking perfect but they are in fact bad.
I'll never push an interference engines belt/chain to its limits, sorry that's just not wise for anyone to ever do. My 07 4Runner (4.7 v8) hydraulic tensioner was totally seized with 95k miles when I changed it. I know its not a common issue but it only takes one time to destroy an engine over belt tension issues. "So' are you lucky punk?" Hey' Eastwood said it not me..lol
Personally before mine did it I had assumed what I saw from time to time was seized from lack of oil changes and I failed to look at the tensioner close enough to see if rust was on the plunger/stem making it seize or possibly interrupt movement because that's what my 4.7 did. A hammer wouldn't budge mine. Many seized are low mile vehicles as the tensioner don't move enough, belts weaken with age too on them so change it if its old. My knowing it happens regardless of oil changes I'll never leave a hydraulic tensioner on for another 100k mile round like many people say they do. Really idk what Toy/Lex states on the tensioner matter and I don't care after what I've seen. I'll happily spend the extra $50 for a new one every single time.

Chains stretch and generally rub on guides as already mentioned but if its not heard or simply ignored too long the chain can skip a tooth or even fall off its sprockets. Anytime after 120k a chain setup is on borrowed time. Personally I prefer timing belts because I know they are much cheaper over the life of the vehicle, they last nearly as long today and with no sprockets to buy with belts, today its much cheaper in the long run! People complained about belts, somebody listened and now stealerships make a lot more money. So be it!

Fwiw- All Nissan & Infiniti engines are interference engines regardless if chains/belt. The old Nissan 3.0 with belt costs $450 every 100k miles vs $1300 every 120k after Nissan updated it to Chain. Called its V6 a 3.5 after changing to chain but its the same engine. Yup!
Sorry long...

Originally Posted by livemeyer

Wow, some interesting takes here, some good information mixed in with some suspect personal opinion. Let me just address the last part with regard to Nissan. I just upgraded to Lexus 450h from a 2003 Pathfinder LE. This is a great engine with a timing chain and is not the 3.0 liter from the 90's! Besides the obvious - that its displacement is 3.5 liters not 3 liters, it also has coil on plug ignition and many other changes that don't come to mind right now. It was my fourth Pathfinder I've owned over the last 30 years, after having owned a 1990 and 1994 (3.0l engine), a 2000 (3.3l engine) and the aforementioned 2003 with the 3.5. That engine was a beast, 240hp and tons of torque. It being 20 years old I wanted to upgrade to something newer, but it was running great with no engine codes at 247,000 miles. Yes, it was an interference engine, as most modern engines are. Frankly, I'm surprised to hear the Lexus 3.5l is a non-interference engine, but it doesn't matter much since with timing chain these just don't break much.

A previous comment about a stretched timing chain, in particular with an older Buick using nylon teeth for noise control, was quite common in the 70's and 80's, but not the case today with modern engines. That part about a timing chain getting stretched and the engine being slightly out of time can indeed happen. However, with modern engines, timing is all controlled electronically, you can't touch it. Not like the old days when you could reach for the distributor and turn it slightly to change timing. These days, tune-ups are mostly a visual inspection to replace worn drive belts, replace spark plugs, oxygen sensors and vacuum lines. One person mentioned that the timing chain does not need to be serviced and generally lasts the life of the car. I want to amend that slightly, that it should last the life of the engine, not the car. Cars rust, transmissions fail, many other factors can lead to the demise of the car before the engine is shot. On the flip side, yes, a poorly maintained engine can cause premature degradation, but that essentially means changing the oil, because there isn't much to be done on a modern engine except make sure it a: doesn't have old oil, b: doesn't leak oil and therefore run without oil, and c: doesn't get overheated due to lack of coolant. Knowing your engine has a timing chain should be peace of mind that you'll never have to worry about it unless something bad has happened to the engine or you're approaching end-of-life of the engine, which I dare say with a Toyota engine could be approaching 300,000 miles or more.

Originally Posted by Nelexus88

The timing chain guides often wear out before the chain does. This can create noise from the front of the engine where the chain runs and can result in timing gear damage if not corrected. Poorly maintained vehicles are more likely to have these issues.