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[quote]QUOTE: Originally posted by Overmod In most cases, the 'rings' in a conventional steam locomotive, as well as their fit, was sufficiently low-tech as to make differential boring somewhat superfluous. As you probably know, the Stumpf Uniflow cylinders had to be machined somewhat 'barrel-shaped' to be reasonably parallel when operating in steady-state due to the temp differential between the intake and exhaust-port ends; locomotive cylinders have a somewhat different profile BUT imho one of the theoretical uses for 'compression' (early cutoff of exhaust) is to keep heat relatively high just at the time intake will begin, avoiding early enthalpy drop. Some interesting 'shoe' arrangements were used to support the piston in engines without tailrods. The ACE3000 was supposed to use 'diesel-style' multiple rings, which wouldn't work well at horizontal support, and therefore had tailrods specified -- this ensured reasonable concentricity under prospective expansion conditions, although I would be interested to see the wear patterns based upon actual steam flow through actual transfer porting under various over-the-road load and speed regimes. [/quote] I imagine side loading of a steam engine's piston is considerably less than an IC engine's, even without a tail shaft. It also seems steam engine rings are quite a bit "fatter" and do not use gas pressure for sealing but only spring expansion. At any rate, steam cylinder bores then are parallel when new. Probably, that was the best that could be hoped for back in the day. It's just that something I heard lately about ring life in steam engines being affected by choice of metal and temperature of steam got me to thinking of my own experience, where changes in bore dimention have a significant impact on ring life. I guess to find a definative answer, I could compare bore/piston/ring spec.s between diesel and steam cylinders. Just a thought, as crosshead guides bearing surface wears, this would probably add to piston side loading quite a bit.
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