All America-bound VW Type IIs (that is, busses and campers) from 1972 through 1979 were equipped with Volkswagen's Type IV engine, aka "the pancake engine", which proved to be the last air-cooled engine VW would ever develop. Many would say (I would agree) that the Type IV engine is also the best air-cooled engine VW ever made, in terms of power and durability.
(The Beetle (Type I) engine (aka "the upright engine"), produced, with improvements but without real change in structure, from 1938 to 2003 (!), was certainly reliable for what it was worth, but the Type IV engine is basically a Type I engine that's had a lot of what's "wrong" with it "fixed".)
One of the pillars of the Type IV engine's strength is its "bottom end", the deepest internals of an engine: the crankshaft, rods and camshaft. The Type IV crankshaft in particular has been sometimes referred to as "bullet-proof". I remember someone telling me once that even God couldn't break a Type IV crank.
It wasn't until (01)Melcher and I were tearing down the engine 10 1/2 years later that what we had expected but couldn't bring ourselves to believe was true: on that hot August day in 1993, McDonald did what the Creator of the Universe allegedly could not:
broken Type IV crankshaft
Nota bene: See "Comments" below for an educated discussion of the above post.
4 comments:
I'm still planning to use the photos you sent me of the crankshaft as part of a presentation I have to do for a Failure Analysis course. If the pictures are good enough we should be able to find where/how the crack was initiated and how it propagated. It's a fatigue failure...more like God bent it back and forth until he was able to overload it, rather than breaking it in one fell swoop.
Interesting to think about. The crankshaft is the backbone of an internal-combustion engine (except for certain Mazdas). It's a really heavy piece of metal that spins around really fast and translates the linear power of burning gasoline+air into the rotational power that moves the vehicle down the road. Despite its heft, as 02McDonald notes, it does undergo some amount of twisting/bending as a normal part of its operation. Twisting metal=fatigue and at some point the fatigue (and very likely not a little overheating) on Ludwig's crank was enough to snap it, like a fork that is bent back and forth rapidly.
Now imagine doing that with a 30-lb. fork.
The fork (or paperclip) analogy is not entirely accurate as an example of fatigue failure...I note this not to be Mr. Smartypants, but beccause the reality is much more interesting. The fork is stressed plastically (permanantly)...a fatigued part is never stressed beyond its elastic (non-permanant) phase. That is what is so significant: a part can be made to fail having never been stressed to the point of the material's yeild strength. Fatigue failure progesses in three phases: 1. A crack is initiated at a surface irregularity (i.e. machining scratch or corrosion divot). 2. The crack propagates at each cycle; the tip of the crack is a stress concentration point. 3. Eventually,the remaining material at the cross section of the failure cannot withstand the applied load and fails. We can probably blame the broken crankshaft on a scratch...and the few times Grady drove (mis-drove?) it.
Is it true then that a crankshaft undergoes some twisting/bending as part of its normal operation? And in this case, it just wasn't that that led to its failure?
So, assuming the engine had never been apart, it must've been a manufacturing flaw at VW (or not even really a "flaw" at all, but simply a minute but within-tolerance variation within or on the metal)? How small can these scratches or divots be to lead (eventually) to such catastrophic failure?
As for your last speculation, I never mis-drove the vehicle, because I never drove it until 2004, and the crankshaft broke in 1993. Nice try.
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