I have no firsthand knowledge of why the difference in belt lifespans. Note that lifespans are in terms of a time limit such as 7 years as well as mileage. It might be due to the belt material selected, another guess is the diameter of the pulleys, yet another could be the running temperature inside the belt housing. Belts are made partially of rubber which hardens with the application of heat over time and I don’t know what happens to the reinforcing fabric or fiberglass due to flexing. Larger diameter pulleys mean less flexing and also less tension stress on the belt especially if the crank pulley, the smallest one of the setup is larger too.
No, you can not look at a belt and judge its condition. Wear is not visible on mine when I change them out at 60,000 miles and compare them visually to the new belt.
Note that higher end cars such as BMW, Cadillac and Mercedes use timing chains. If belts were overall a better choice, then that is what they would use.
Another factor might be the number of pulleys. A SOHC I-4 with only a tensioner pulley might be expected to last longer than a DOHC V-6 with idlers and a tensioner.
Like others here, I’ve never been invloved in the design aspects of either the belts or the engines, but these criteria seem logical.
Because the van is clean and polished, you assume that the previous owners (there could have been several owners over the 8-9 years that this vehicle has been in service) were scrupulous regarding the servicing of the vehicle? That is quite an assumption, and in fact this is a potentially expensive assumption.
A child may be well-dressed, but his parents may ignore immunizations and child well-care checkups, and may feed him junk food.
Similarly, a car owner may be obsessed with cleaning his vehicle, but may be clueless (or uncaring) about vehicle maintenance.
Or, in other words, appearances can be deceiving and can lead to expensive problems if someone does not do his/her due diligence.
I realize that your cash flow probably dictated buying the cheapest possible vehicle, but you have to be aware that there will probably be pitfalls when you buy a vehicle with a low price as the primary criterion–especially if you don’t have its maintenance records.
When you buy your next vehicle, you need to find out about things like timing belts and the maintenance record of the particular vehicle BEFORE you buy it. Assuming the best about its maintenance after you purchase the vehicle is going to make you prone to some very big repair bills–perhaps bigger than you can afford to pay.
That is correct.
Visual appearance of a timing belt is not a reliable indicator of its condition.
A timing belt can appear to be in very good condition, and it can snap within hours–with very expensive consequences.
“2) on engines with a timing chain replacement of the water pump will not in any way require intereference with the timing system of the camshafts (the chain). IMHO being able to change a failed water pump as an individual component is an asset.”
Unless of course you’re working on a GM Quad-4 or one of its unfriendly derivatives. The water pump sits to the REAR of the timing chain on the backside of the engine. NASTY pump to replace.