What I was trying to get over to you is that no mater how good an item is machined if it's sliding against another it will wear, oil or no oil, which you concede that Gondola's pistons have slight wear, slight though it may be it's still wear and a credit to the manufacturer that after 30 odd years the wear is slight.
The reason for full size pistons and cylinders being cast iron is that casting process is much easier and economical that of any other material although some of the big engines had steel pistons.
You say that with your (bad) tolerances they will not be touching, well what will happen is that the gases will pass the piston and give poor power results and large steam consumption but a beautiful column of steam from the exhaust as no amount of steam oil will seal between the cylinder wall and the piston.
Why not make new pistons and fit them with Silicone "O" rings which make a good seal and if your piston tolerances are a bit out the rings will take up the slack., you could even use graphite packing to make a seal, Gondola's pistons will have rings fitted which can be replaced if required without making new pistons.
You then go on to say that your pistons will be touching the cylinder wall which I assume you mean that the piston will be size for size with the cylinder wall
if so size for size doesn't work it will seize. .
D10' can rev up to 2000 rpm but in a model launch I would think more in the range of 800-900 and I don't think that Gondola will be any where near that but I am sure that you could let me know what it revs at cruising speed are.
Hi George,
I believe you don't quite get my sense of humour, or it doesn't come across in my posts- either way, I was intimating humourously that my machining skills were not upto the standards of yourself for example, but apart from machining them, I have a very extensive knowlege of steam engines and their running characteristics.
As such I am well aware of the running clearances of pistons in cylinders, and mine are ok, if perhaps slightly on the larger side- If I get problems with large steam consumption then I will know how to remedy it, but for the moment I will stick to the ones I have machined.
Gondola's engine was rebuilt by Roger Mallinson, one of the best small marine engineers in the country, as such the 'wear' is less than 0.0015". She runs at a cruising speed of 7/8mph @ 180-200rpm, max 12.7mph@380rpm.
She has a bore and stroke of 8" X 9"- giving a piston speed @200 rpm of 1800"p/min
My D10 has a bore and stroke of 3/4" X 3/4", and will be running at a cruising speed of 450rpm, giving a piston speed of 337.5" p/min- nowhere near what Gondola's is, and producing far less power and torque is incomparable for a point of view of wear.
I do like the idea of Graphite packing though, and I understand it used to be used frequently by Stuarts in their engines?
Greg
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Topic: Materials for steam engine (Read 11726 times)