QUOTE: Originally posted by O.S. Jruppert: I greatly appreciate your expertise in engines -- I'm learning a lot from you and Peter that isn't really obvious in the engineering texts. But -- you knew that would have to lead to a "but" -- I don't think that War Production Board restrictions were really anything more than an excuse invented by railfans years later to explain away the failure of their beloved Alco. If one looks at the historical record when it's written by historians who don't have a pre-existing agenda to absolve Alco, it seems clear that Alco's most serious problem was that EMD had been developing a diesel engine since the early 1930s, and Alco hadn't. It was a very new and high-risk technology, and Alco waited far too late to get started. By the time they did, EMD had made all the mistakes that Alco was still destined to make, and EMD had solved them and Alco didn't even know what they'd be yet. OS
QUOTE: Originally posted by Overmod Weirdly enough, I would NOT have expected most of the crank breaks to be at the flywheel end. I'd have thought somewhere in between pairs of cylinders inducing the greatest mutual torsion... not working against flywheel inertia. I learn something every day from Randy... Where were most of the breaks on the 16-cylinder 244s? (I've always wanted to know that!) This isn't directly germane to *locomotive* crank breaks, but IIRC the breakage of GM truck diesel cranks is often somewhere other than at the rear main bearing. I read an account of one person with a 6.5TD who had a broken crank between the first and second pairs of cylinders. His complaint was that the engine ran a bit rough, and only seemed to make about 75% power... he was so right! Only the rear six cylinders were actually providing effective torque; the two in the front were mainly driving the auxiliaries; there was just enough interference between the two broken halves that they stayed in rough sync (think about how the injection pump wandered in and out of 'time' though, depending upon effective torsion... !)
QUOTE: Originally posted by Overmod I suspect that the 'long term' effects while substantial may be easy to document. My understanding is that EMD engines with bad power packs are fairly common in service, and often the engine isn't pulled for service until a certain number of them are dead. (Whether or not the engine is pulled immediately for something that isn't an individual-cylinder failure is another matter). Randy, is there any 'preferential' location for powerpacks to go bad? If not, there can't be any good prediction of what the torsional stress in the crank would be, or what the long-term implications of peak stress might entail. It's been my suspicion for some time that dead cylinders were a major contributing factor to some of the crank breakage on the 20-cylinder engines. Other reasons why two-strokes don't make 'twice the power' of a four-stroke: a scavenged engine doesn't have the charge density of a four-stroke with intake valves in the conventional position, given equivalent levels of boost. I can't find the reference to 'bmep', but the effective cylinder pressure on a two-stroke might as well be no higher than boost pressure by the time in the stroke that the scavenge ports begin to be exposed, or you'll start to get gas cutting on the rings, one of the places you'd least want it. Oh, by the way, there are a couple of 24V71s on sale if you want 'em. TA's, too! http://mdeltd.com/product.php?product=Marine%20Engines (Scroll down the page a ways to find them) Nifty looking things; they don't look to me as if they use a pair of 12V71 cranks bolted together, either... There are apparently quite a few yachts that have these things. One wonders, though, how many hours you'd get if you got 1800hp @ 2300 rpm out of them for any length of time <8-O
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Our community is FREE to join. To participate you must either login or register for an account.