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[quote]QUOTE: Originally posted by M.W. Hemphill John: Absolutely. You've been an asset to this forum, and I've learned a lot from you. The question about bore taper in IC engines I know I have seen as the practice for very small bores, but I don't know why one would bother in a medium-speed diesel engine such as an EMD, which has very loose tolerances -- for instance, the main bearings are not scraped to fit. [/quote] When you say scraping do you mean hand scraping? Hand scraping while highly accurate, is not done anymore, and is a lost art. My stepfather showed me how it basicaly is done, but it takes a long time to truly master. You can always tell a hand scraped surface by the pattern of the tool marks. Main bearing bores in blocks too large to fit in a boring machine have to be align bored by a portable boring bar supported by spacer bushings between two bores separated by the bore to be cut. End bores are cut by supporting the bar from two inside bores. What may be considered a large bearing oil clearance, may be absolutely necessary for a large journal, as a journal's diameter increases, so does the necessary oil clearance. If loss of power cannot be attributed to anything simple like an air filter, or crankcase breather. Or, possibly fuel rack setting, or other mechanical reason, then loss of cylinder pressure must be checked. Diesel engines are not compression tested like gasoline engines because while compression pressure may be somewhat higher, they can vary quite a bit under different conditions. The only way to check for loss of cylinder pressure from general wear is to inspect the liner, rings, piston, valves, liner/head sealing, and determine if replacement is necessary. That stuff is old school nowadays though. With electronic engine management systems, a preprogramed diagnostic routine can be run, where the computer runs the engine at a set rpm, cuts cylinders out one at a time, comparing data, and determines performance of each cylinder.
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