engine tightness

This topic has 8 replies, 5 voices, and was last updated 14 October 2019 at 20:20 by mark costello 1.

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12 October 2019 at 09:26 #432915
Philip Burley
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@philipburley44197
Hello , I have built a ST no I engine , 2 in X 2 in, Thing is , how tight should it be ? It turns over , but not freely . run it in on the lathe for half an hour and runs on air . It has home made iron rings . Previously made mill engine and a beam engine turn much more freely . . I just wondered if the piston fit or, the rings are too tight Can any one with a similar engine tell me how easily there's turns over

regards
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12 October 2019 at 09:26 #9890
Philip Burley
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@philipburley44197
12 October 2019 at 18:37 #432979
John Purdy
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@johnpurdy78347
Philip

I have just completed a ST#1 (see my post of 21 Aug. in the "work in progress" thread) and it turns over with some drag which I put down to the ring friction in the bore, but I wouldn't call it tight. It uses the supplied ST rings and are fitted with an approximate 3-4 thou gap. During initial testing I assembled it without the rings and it that state it just spun over easily and if the flywheel was given a good spin it would coast for 2 or 3 revs. Try assembling yours without the rings and see how it goes, it may be just the ring to bore friction that is causing the tightness. How thick are your rings? The ones from ST in mine are .0955 thick, which are by all accounts considerably thicker than optimal. The wall pressure may be higher than optimal. I found that I could remove the rings without disassembling the whole top end by removing the the top cover, and with the piston at TDC the nut could be undone and the top half of the piston unscrewed. Lowering the crank to BDC then left the rings in the top of the cyl. and could be removed. With the crank back up at TDC the piston could the be re-assembled. I must have done this a half dozen times!

John

Edited By John Purdy on 12/10/2019 18:40:52
12 October 2019 at 19:26 #432989
JasonB
Moderator
@jasonb
Is your bore just the turned finish? honing will give a smoother bore with less initial friction but with still enough of a surface for the rings to bed into. A good oiling and running on air for a while will also help, just watch where the black oil coming out of the exhaust goes.
12 October 2019 at 19:28 #432990
Neil Wyatt
Moderator
@neilwyatt
Ring pressures for steam can be VASTLY lower than for IC engines.

Neil
13 October 2019 at 19:14 #433143
Philip Burley
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@philipburley44197
my piston isn't made in 2 halves so not quite to easy to remove the rings to check it without the drag of them , but I will dismantle it and check . The bore wasn't lapped , but it has been run on the lathe for half an hour well oiled , Thing is , should the engine spin over a couple of turns , or is that expecting too much ? . It certainly wont at the moment . but it turns with a finger in the fly wheel , Not having anything to compare it to is the problem

regards
14 October 2019 at 11:50 #433242
Philip Burley
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@philipburley44197
I think I am worrying too much !! after all it works , so cant be much too tight , its just the newness !!
regards
14 October 2019 at 20:19 #433335
mark costello 1
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@markcostello1
Why does steam get less ring pressure?
14 October 2019 at 20:20 #433336
mark costello 1
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@markcostello1
Why does steam get less ring pressure? Please delete.

Edited By mark costello 1 on 14/10/2019 20:20:57
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