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Post by joanlluch on Apr 30, 2015 10:32:10 GMT
hi joan, there is not the slightest difficulty buying piston rings for cast iron cylinders in miniature locos. Stuart Turner and Clupet have been making them for generations. there is no reason why a 1" dia bore should not be turned to 25mm etc. however both Doug's sets of cylinders are gunmetal. cheers, julian Hi Julian, thanks for that. Is there then a reason why you wouldn't use standard piston rings in cast iron cylinders or liners? Thanks.
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Post by Roger on May 5, 2015 19:37:47 GMT
Joan has put me onto a couple of potentially very useful products that I ought to share with you, these and these. There are both piston and rod types in the first of these although I'm not sure whether the sizes are going to be available to make them suitable for piston seals. Although they do a metric range, 38mm isn't one of them. However, they do cover the 5mm and 8mm sizes for the piston and valve rods that I'm using and they look very good indeed for that. The material is PTFE and they are sprung. They are specified to run at high temperatures, high speeds and high pressures so they ought to be ideal for piston rod seals from the look of it. Anyway, I'm going to see if they're available at a reasonable cost in the UK because they would appear to be a better bet than Viton 'O' rings.
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Post by joanlluch on May 5, 2015 21:44:13 GMT
It's certainly a bit odd that some few sizes are not available. They have everything almost millimetre by millimetre up to 25 mm, but then some greater sizes are missing. You have 35, 36 and 40, but not 38. Trellebourg produces a fair amount of imperial sizes as well, so this may be something worth to consider by others as well. I have more luck as my pistons are 50 mm diameter which is one of the available sizes.
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Post by hprings on May 11, 2016 19:56:58 GMT
Michael, Thanks for your response. I haven't been able to find your reference thro' the Search box. I had, & still have, reservations about Cr plated rings with GM, not necessarily based on personal experience but from when doing some research into valve guides made from Colsibro etc against Cr plated valve stems in high speed ICEs. Undoubtedly hard chrome plating is extremely wear resistant and using Cr plated rings will wear the GM bores. My probably false reasoning was that I'd rather eventually replace the rings than have to rebore the cylinders. The aforementioned metallurgist Alan Smith of Clupet was adamant that the softer metal (GM) would outlast the harder one (his centrifugal CI rings) due to particles being embedded in the softer GM. I couldn't envisage that happening with hard Cr plated rings. However it's appreciated that an oil layer at the interface could have a profound effect on relative wear. But then I've yet to identify a lubricant that won't char in the superheater wth steam at 150+ psi. Adding powdered graphite or molybdenum disulphide to a high temp steam oil might be a solution. Ian C.
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