Where is TDC on a beam engine ?

Is TDC on a beam engine when the piston is at the bottom of its stroke ie piston rod fully depressed or at top of stroke, piston rod fully
extended ? This is baffling me. I need to know this so as to time mine, in the instructions it says get the piston to TDC and the bottom port should just start to open.
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stereotype
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Piston at the bottom of the cylinder, at least thats the way my stuart beam is timed, the port should just start to be uncovered about 15deg before TDC
If it were the other way round you would be letting steam into the top of the cylinder while the piston was at the bottom which would just hold the piston down
Jason
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stuart
15deg
top
hold
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http://www.rcgroups.com/forums/member.php?u 3943

http://www.rcgroups.com/forums/showthread.php?t 94526
I'm sure that you're right, but then surely the term sould be BDC - bottom dead centre, rather than TDC?
AWEM
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On 20 Aug, 16:55, "Andrew Mawson"

Depends if it's fully advanced or retarded, talking of which..........no forget it, we won't go there today........
John S.
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Yes when the beam engines piston is at the bottom of its stroke it is BDC, when at its top its TDC.
The point I was making is that your instructions sound like the ones you can download from Stuarts site and the engine won't work if you follow them, think they were writen for vertical engines. If it had said with the engine at TDC the top port should have just started to get uncovered then TDC would be right.
Jason
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On Sun, 22 Aug 2010 07:35:54 -0500, jasonballamy

TDC refers to the crank position not the piston position. In a traction engine, there are front dead centre and hind dead centre.
Mark Rand RTFM
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Jason thanks for your help. The engine I have built is the Vulcan and the instructions came from the Model Engineer circ 1953/54 the timing advice they give is very confusing, seems their TDC should have read BDC. David
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On Sun, 22 Aug 2010 13:37:29 -0500, stereotype

Hello David, No, TDC is TOP DC even when it's down. An inverted aero engine for example still has TOP DC when the pistons are down. A Napier Deltic would be a tesaser - 'a bit sideways-dead-centre'?.
It refers to the piston/cylinder-head relationship (or Piston crank). Piston nearest head/Crank-conrod-piston extended = 'Top' Piston furthest from head/Crank-conrod-piston compressed = 'Bottom'
Richard
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