Hi RecycleBill / All:
This is a very interesting thread - thanks for raising it Bill. If I may, I'd like to contribute a few thoughts....
Timing chains have almost completely disappeared from modern automobiles but still remain common on motorcycles. But could that be about to change? And could it be that someone who reads this forum becomes a pioneer in making that change take place?
Actually, many modern vehicles are moving away from timing belts and to timing chains (several have been named by others but I know that my 1994 NA Miata had a belt but my 2006 NC Miata has a chain - ahhhh....no worries and no servicing beyond oil changes.
Having said that, some OEMs are having major headaches with very complex timing chain drives (Ford 3.5 litre ecoboost, BMW N20 four cylinder, and many Audi models) - so chains ain't perfect. The problems seem to come when the chain has to drive more than just a couple of camshafts - the thing gets too long with too many wraps around chainwheels and positive and negative tension conditions around the mechanical circuit.
You speak of short replacement intervals of 40 and 60 000 km. Those BMWs must have really got punished hard. I've bought lots of old Toyotas with the original timing belt broken at 250,000 miles (402,000 km) replaced the belt then sold the car to someone who drives it another 100,000 miles. Factory recommended replacement of timing belts on those old Toyotas was 100.000 miles.
Yes - the typical service interval on older belt drives was 100,000
km, at least here in Canada, and not 100,000
miles (that would be about 162,000 km - and you'd be well into very risky territory at that milage).
I've bought lots of old Toyotas with the original timing belt broken at 250,000 miles replaced the belt then sold the car to someone who drives it another 100,000 miles. I'm sure pulley size has something to do with the long life. I always steered clear of the old Nissans as many of them were valve crashers.
Many older lower-compression engines are "non-interference" designs and so a broken timing belt or chain means a tow and a fairly simple installation of a new belt/chain, but some engines (generally the higher performance models) are what is known as "interference engines" which means that the valves will collide with the piston crown - or with each other - if the camshaft timing gets too far out of whack.
I must admit that I hadn't heard of the belt-in-oil design. As first blush, it sounds OK but I'd want to see some long-term durability data on the belts with different grades of oil.
Finally, I agree with Gary: there is little difference in efficiency between a well lubed chain running at the correct tension and a properly tensioned belt. I do recall when Harley went to toothed final drive belts, they claimed some milage bonus but I have never seen any data to back that up.
Pete