Thanks Don, great answer for Chuck,, guys,, I have seen many an engine, self destruct when the timing belt, chain or gears fail due to high mileage, but there are not that many interference engines now days.
When an interference engine does self destruct, normally the whole engine is just junk iron, except for the injection pump, alternator an starter, an smaller parts. One or more valves tend to go thru its companion piston, swelling it, an cracking the cylinder block, an often the cylinder head too.
Engine techs or Enginemen call that a piston trying to swallow a valve, that swarms the engine. The valve an piston try the basic law of physics, that says that two items cannot occupy the same space at the same time.
Many of the older small engines, mostly 4 cylinder, used rubber belts for timing / driving the valve train, these belts had teeth that would shed from age, an wear, resulting in a destroyed engine, at maybe only 60,000 miles, thus we tended to change the belts at 50,000 as a normal PM an sort of insurance against an angry car owner.
Chains are much better, they have tension arms, spring loaded that hold the chain in adjustment automatically, along with nice chain guides, but they too wear out.
Sometimes on Diesels, the oil pump is also driven by a chain, that is a part of the valve chain system, thus with wear excessive its a two part threat to the continued life of the engine.
Not sure about Mercedes, not yet all that familiar with the overall design of the engine systems, yet, have not worked professionally on Mercedes, just minor maint. items in the past 6 years since I have owned my 300d an SD.
Valve timing failure is about the same as when the SD turbo sucks in water, thru a failed air intake hose, an the engine self destructs, happens all the time here in the Texas Gulf Coast area, during flooding, an normally the whole car is junked, many are crushed too.
Good low mile used engines for such old cars is almost impossible to buy, an sometimes they will sell for up to 2 or 3 K, depending on who is selling it.
I will not risk my cherry engine past 200K, will change the timing chain early next year, when I reach that mileage, my 300d is too important to my financial health at this time, after 11 years of fixed income, being retired.
Have a great weekend, the Texas weather is wonderful now.
Doug, East of Houston, '78 300SD garage queen, '81 300d daily driver, Diesel fuel $3.69 now, gone down 30 cents this month.
