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Post by donashton on Aug 9, 2014 12:25:26 GMT
Can't give you an ad hoc answer without going back through my simulations and notes. Please wait - it was rather a weird case in the first place.
Don.
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Post by AndrewP on Aug 9, 2014 15:34:46 GMT
Marc, From memory leave the rods the same length but un cross them and the valve size is ok. I made new expansion link and die blocks to Don A's dimensions and replaced all roll pins in the linkage with proper taper pins since a broken roll pin had been my original problem. The reverser goes the wrong way now but that is mildly amusing if somebody else drives. Performance is transformed to the extent that I try and keep the boiler pressure down to around 60 to reduce the wheel slip and intend to add significant weight this winter. Andy
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Post by donashton on Aug 9, 2014 16:22:57 GMT
Hi Andrew,
I'm just trying to refresh a bit cos it's a while since the original nightmare!
I'm rather amazed at my own 'thinking outside the box' on this one and am pleased that you have had success.
Cheers,
Don.
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Post by donashton on Aug 9, 2014 20:29:37 GMT
I'm feeling very dishearten at the moment.
Don't! The information you now have contains very little work and Andrew has done it and recorded the success. Understanding what I have done is quite a separate thing - I only included this for those interested. Uncross the rods if they are crossed at present, attend to new trunnions, and reset the valves. I wish I could cure everybody's valve gear problems with so little work.
Don.
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Post by Deleted on Aug 9, 2014 23:30:27 GMT
HI DON--------- as the heading for this thread is}--- Stephensons Valve Gear, can I ask have you ever cast your eye over Peter Rich's gear for his 5" Star/Castle design ??Anything we need to be aware of at all ?..Thanks---PS, When will you be in attendance at Llangollen Works next ?......I'd like to ride over ( 1975 HONDA GLl000 GOLDWING )have a chat / buy you a beer ??
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Post by donashton on Aug 10, 2014 7:39:52 GMT
Marc, I have never mentioned a change in rod length - just a new trunnion setting and a valve reset.
Alan, I haven't seen Peter's drawing (always immaculate) but he usually kept strictly to scale. Llangollen? Well, yes, but how come the modern bike! Ah, maybe a misprint.
Don.
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Post by Deleted on Aug 10, 2014 9:51:11 GMT
Hello DON------ er, 1975 makes it a tad under 40 years old which is older than some Classic Brit. bikes currently doing the rounds...Dear TAFF's drawings do indeed look as if lifted direct from the Swindon originals...I'll build as drawn then and we should be ok....
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Post by Deleted on Aug 10, 2014 14:50:01 GMT
Alan, The Castle and Kings have Walschaerts valve gear. Nick --------------- Thanks NICK ,I am aware of that but old age and "Typos" are no respectors of dignity, alas !!! Thanks anyway for that heads-up...No one else noticed, did they ?
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Post by donashton on Aug 10, 2014 15:10:19 GMT
Alan, Tempus fugit. Regarding Castles and Kings I once posted that their respective gear settings were not the same. Peter immediately dashed for his drawings and had to accept that I was right - didn't stop us remaining good friends. The Large Teddy was presumably the father but could take the later gear for whatever advantage if you wish. While Nick is technically correct, I wonder why the immaculate Willie Pearce Stephenson's gears were not used on the 4-cylinder engines. That would produce top class events before driving through the rocker. Cheers, Don.
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Post by AndrewP on Aug 10, 2014 21:40:56 GMT
The last section of Don Young's build details for MarieE is titled Oops and proceeds thus:- Oops! Verily, he who takes a short cut comes unstuck. It concerns the valve gear, which was lifted directly from my 3 1/2- in. COUNTY CARLOW design and which will appear in these pages for SAINT CHRISTOPHER. Knowing I had a correct and proven valve gear at my disposal, plus it was a perfect fit in the space available, I reasoned it out in my head, (which was asking for trouble!) instead of setting it down on paper. Thus for the 'primary motion' I reasoned that the reversal of direction by use of the leading axle was balanced by an equal and opposite reversal through the medium of the rocking arms; so far so good. What escaped my notice was a reversal of the 'secondary motion', that covering the lead function, and by not taking remedial action the result is a gear in which lead reduces towards mid-gear, a case of what makes a Steam Locomotive stop ticking! I have to thank builder Dave Churchman for opening my eyes to this discrepancy; not the best Christmas present I received, but certainly the most timely. Now, because the basic valve gear is O.K., it is a matter of manipulation rather than wholesale scrappage, and there are three possible solutions. The first leaves the valve gear exactly as per drawing and shortening the valves by 1/32 in., reducing the 31/32 in. dimension to 15/16 in. and increasing lead in full gear from the specified .005 in. to .020 in.; this will result in a better working engine. A second way out is to leave the valve itself well alone and at the position shown on Sheet 2 of the drawings, merely swop over the two eccentric rod ends on the expansion link, this to give 'crossed rods' which results in an increasing lead function and is therefore the correct solution of the valve gear. Leaving everything else strictly alone, there is one small side effect in that the reverser pole comes towards the back of the cab for forward running and to the front for back gear. The 'ultimate' solution is to cross the rods and then move the pole fulcrum above the reach rod pin, this to reverse its motion and give conventional pole movement. Over the holiday period I have had time both to reflect on the folly of my ways and the best possible solution, my conclusion being to recommend the second approach of simply crossing the eccentric rods and leaving all else well alone, for my attempts to redesign the reverser only ruined its graceful proportions.
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Post by livesteambookham on Oct 12, 2014 22:41:30 GMT
Hi Don,
I am thinking of building a Marie E and would be grateful for your Word document suggesting a solution to the valve gear problems. Please let me know how I can obtain them and how much I owe you for postage.
Many thanks, Mark
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Post by livesteambookham on Oct 12, 2014 22:43:30 GMT
Hi Don,
I am thinking of building a Marie E and would be grateful for your Word document suggesting a solution to the valve gear problems. Please let me know how I can obtain them and how much I owe you for postage.
Many thanks, Mark
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Post by donashton on Oct 13, 2014 8:01:58 GMT
Hello Mark,
Send me a PM with your email address.
Don.
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Post by ettingtonliam on Oct 13, 2014 13:13:13 GMT
I'm confused (more than normal) Don (Ashton) says the cure (or part of it) is to uncross the rods, and Don(Young) seems to have said the cure was to cross the rods.
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Post by donashton on Oct 13, 2014 16:12:16 GMT
Don't be confused. Crossed rods are very rare so forget crossed rods, which have no business on locomotives.
Don.
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Post by ejparrott on Oct 13, 2014 16:46:49 GMT
I'd go with Don A rather than Don Y!
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Post by donashton on Oct 13, 2014 17:17:17 GMT
Well, give Don Y his due - he dug into a hole with this oddity, but in general he produced a host of good engines as a legacy.
Don (A)
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Post by donashton on Oct 13, 2014 19:26:13 GMT
Hi Andy, No problem, as Stephenson's gear doesn't need an overcoat, especially on Thursdays. Don.
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Post by joanlluch on Oct 14, 2014 11:28:02 GMT
It would be useful that both the original and the modified geometry by Don A. be posted so we can all learn from it.
Joan
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