I have often wondered the same thing. Ford's 2.0 8v (DOHC) engine fitted to the Sierra never gave any bother, my one was on the origianal which was 16 years and 115k miles old when I sold it. The newer Zetec engines switched to belt iirc, it's just an extra expense. I reckon it's just to give the garages something to do because there is very little profit in just selling a new car, the labour charges on servicing are a great source of income.
+1 As car technology has got better, there is less and less serviceing required, even oil lasts longer and works better now, timing belts get cars back into the workshop, and justify its existance.
As to the noise issue, a petrol with a chain is quieter than a diesel with a belt.
Oh and my Dad was a mechanic from the late 1950's to the early 1990's and saw belts become commonplace on cars, he can't see any other reason for them either (on "Normal" car engines-see below).
I seriously think that choosing belts over chains has other reasons than just to give a mechanic something to do....
But perhaps costs are a factor. Obviously it costs more to design an engine with a chain than one with a belt, due to proper lubrication, etc...
A small hole in the casing below the cams (which are still lubed, and at the top of the engine) and gravity will oil a chain for damn near no cost.
One area where a chain is difficult to work is the tight curves required to get a chain around a multi cam head, or two in the case of a V6, the cam drive wheels have to be a certain size to fit in the engine , and the driver wheel has to be a certain size to drive them, at the correct speed, with a quad cam V6 the wheels driving the cams cannot have a diameter greater than the distance between the camshaft centres, and I think the drive wheel needs to be twice the size of the driven wheels (thats a guess-put me right if needed), yet a chain cannot go around as small a wheel as a belt...
One other thing, oft times its the pulleys or tensionors, or waterpumps that seize, fail or whatever, which in turn snaps a good belt-any thing that moves and touches a belt must
be changed with the belts
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I pop in here to have a look now and again-but don't know what to say
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