> David Carment writes:

> Just looking over these figures there seems to be an inverse relation
> between engine wear and known engine-life length. In other words, we all know
> diesels have a capacity for long engine life... aircooled vanagons on the
> other hand have been known to last less than 100,000 before
> overhaul....and Porsche engines?  I am wondering if there are intangibles
> built into each engine type that the wear index does not encompass or
> alternatively the VW engineers had anticipated knowing that for example
> Diesels would take more punishment and therefore made them extra strong...DC
> 
> 

  I very readily agree that there are many intangibles that affect engine life.
  The wear index gives only a relative measure of how much friction is occuring
  between piston and cylinders. As you point out, air-cooled vanagons have a
  reputation of needing an overhaul at 80,000 to 100,000 miles. I think we 
  will find most people agree that it is cylinder head / valve failure that
  drives this, not worn out pistons, rings and cylinders. As you have 
  undoubtedly read here on the list, a common failure symptom of the diesel is
  blow-by. This is a result of wear in the area that the wear index does
  measure. The reputation for long life that is associated with diesels is a 
  result of the heavy-duty nature of a) truck engines  b) the Mercedes Benz and
  Peugeot automotive diesels and the fact that they have a relativly low
  specific power output for their displacement and that power is usually
  developed at a low relative rpm. Not all diesels have a reputation for long
  life - take the Oldsmobile diesel V8 for example. IMHO there are other 
  factors that help diesels last: the fuel is a lubricant rather than a 
  solvent, the absence of a spark ignition system help keep them in tune and
  running efficiently - not dumping copious amounts of heat into the head
  due to improper timing, incorrect mixture, etc.

  Back to intangibles: I'd be willing to bet that a wasserboxer engine that
  never had a bout of overheating due to cooling system maladies would last a
  very long time. Type IV engines that don't develop valve problems have very
  long lives before piston/cylinder wear becomes apparent. One neighbor of mine
  put 170,000 miles on his '72 before the heads needed to be done. The pistons,
  rings and cylinders were not changed and now have over 200,000 on them. 
  Another neighbor took apart the engine in his '78 at 120,000 because he 
  thought it ought to be worn out. He found nothing wrong and put it back   
  together with new exhaust valves "just in case". The engine subsequently
  found it's way into the double bus (two buses welded together) and was used
  until he changed it out for a Ford V6. Total accumulated mileage is unclear
  but it's up there. 914 VW/Porsches have a reputation for very long engine
  life - their heads may last longer since it's likely they spend less time
  at full throttle than a bus. 

  I think it would be both fun and interesting to collect and organize list 
  data on accumulated mileage and repair frequency. I even know of a "data/
  statistics pimp" who could probably suggest some good ways to organize it...

  Kautz