This discussion could run and run, but I think from a user's point of view there are clear options which I list below in order of preference. My definition of "preference" is lowest maintenance costs to the owners of these vehicles - although purchase cost clearly is a factor in the longevity of any design.
Best option: A drive which will last the life of the engine to which it is fitted without attention. This could be a geared drive or a generously engineered duplex or triplex chain drive with a rolling tensioner sprocket - as used on earlier M-B engines.
Next best: A toothed belt drive in an accessible location which can be renewed once or twice (say) during the life of the engine. Belt drive components cannot be oil lubricated and the main failure mode is the lubrication of the rolling bearings of the tensioner/idler wheels. Grease lubrication here is marginal as these bearings are bolted to the block and run hot - so the oil component of the grease runs out.
Worst: A chain drive which requires renewal - an expensive job. Almost any single strand chain drive is not robust enough to run to engine life and some designs are made even worse by having crank sprockets with too few teeth. An example of a drive which many people have found to be non-durable in use is the single row chain used in some M-B engines.
For the average motorist, a good and accessible belt drive will give the best value for money as the purchase price of option 1. is high and the choice very limited.
In a belt driven system no grease lubricated idlers will run to the life of an engine (the belts probably would) so routine attention is essential. If vehicle makers had the good sense to consider belt accessibilty in their designs, maintenance would not be the issue it clearly is.
Option 3. is a disaster - a very expensive job at a time when the capital value of the vehicle is at a low point. Time to scrap.
The engine which is the subject of this thread may well prove to belong to this category as its durability becomes known.
659.
Edited by 659FBE on 15/04/2012 at 13:51
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