[modeleng] Re: Piston rings and O rings
- From: "John Pagett" <john_pagett@xxxxxxxxxxxxxxxx>
- To: <modeleng@xxxxxxxxxxxxx>
- Date: Sun, 15 Jan 2006 14:33:28 -0000
Nigel,
Everyone has their own opinion on this, but with cast iron cylinders (the
usual on a Sweet Pea), I'd would (and have) stuck with cast iron pistons and
rings. In fact, although I bought some iron rings from Blackgates, I made
some new ones from continuously cast iron. This was after I'd read some
articles in ME about how much wall pressure you actually need from the
springing out of the rings - not much in a steam engine, compared to
internal combustion.
If you do insist on using o-rings, you will need to make sure that the
finish in the bores is as good as you can get it, or else the o-rings won't
last 5 minutes, as some of the guys building well known kit locos will be
able to tell you.
The biggest problem I had with the design as published was keeping the
pistons concentric on the rods - if you do the final turning with the piston
on the rod, make absolutely certain that the piston can't tighten itself
whilst the turning progresses. If I was doing it again I'd use the thread
solely for attachment and locate using a taper or parallel section of the
rod.
Having said all that, I'm still a few months away from an air chassis!
Regards,
JohnP
>I am currently building a Sweetpea and have come to start the cylinders and
>pistons, I am looking at the piston rings and have been told the I would be
>better off using a Silicon O ring instead of piston rings, I need to know
>how
>wide the slot should be to allow the ring to rotate.
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