Here’s a couple of questions which I thought that I’d put to the wisdom of the forum:
As many of you know, I’m doing an in depth mechanical restoration (the cosmetic work can follow once I’m happy with the mechanics) on a 1922 Stanley 740D Roadster with a standard ish(!) 20hp engine. The engine restoration is nearing completion and I hope to be in a position to set up the valves in the next couple of weeks.
My first question is: What would be the correct cut off to set the valves to for the hooked up position? I have a new weighshaft lifting arm as the original was cracked, and I have the luxury of being able to adjust it’s position on the weighshaft before finally cutting the keyway.
Secondly: whilst working on the engine frame, I noticed that the reverser quadrant is fitted 180º to what I expected i.e. below the weighshaft tube, and a rather nasty adaptor had been fitted to the reverser arm to extend it above the weighshaft tube so that the rods from the pedal and button could function in their intended manner. The action and mechanism work in the normal way. I cross checked with my 735 and sure enough the quadrant is above the weighshaft tube as expected. This mod seems to be ‘two wrongs to make a right’ – has anyone encountered this before? There seems to be no benefit to inverting the quadrant; no space is saved as the reverser arm has been extended upwards anyway! I just can’t think why the reverser has been configured like this.
I can't answer your second question - sounds like one of those alterations which are done for some reason known only to the perpetrator but which seemed like a good idea at the time.
Here comes another one!
As you have to find the best setting for the hook-up can I suggest that you engineer a nicely adjustable hook-up quadrant so that you can move the notch to the optimum once you have the car on the road. I think it's pretty difficult to adjust this to the best position before fixing the quadrant in place - running on air or even on steam off-load isn't going to give you a representative answer. My hook-up lever came free from the shaft so I had to recover the position, made a temporary connection and played around with it on the road. The result was better running than before - the cut-off was actually too short as originally set up.
Interesting experience driving the car a short distance home with the hook up disconnected. It will only move in the direction it was last going so to reverse you have to get off and push it backwards a bit then drive.
Edited 1 times. Last edit at 10/27/08 04:47PM by Mike Clark.
Posted by: les nelson (---.dynamic.dsl.as9105.com)
Date: December 16, 2008 03:38PM
I am sure there are many and varied opinions about this as valve gears on steam engines are a mathematics nightmare. BUT having built many engines over the years it has always been my policy to make the valve EVENTS equal about the centre this applies equally to Walshearts and Stephenson vale gear , the most important thing to remember with Stephenson valve gear (as on most of our steamers inc. Stanleys') is there is (normally) no lead when in full gear, lead is only obtained when "notched up" to some extent. as an example I run the Morriss in MID gear when cruising, in theory the engine will run in either direction in this state, in fact it does, this gives maximum efficiency with regard to steam consumption as the engine is running only on lead. I suggest the valve gear in the Stanley case is set for equal events and the notch position is already decided by the quadrant, the notch position will be satisfactory , it works for me and the Stanley brothers were no fools. my 735 ran OK, I can recommend cutting a flat plate to represent the valve that can be fixed to the valve spindle, this way it is possible to see acual events, but don't be suprised if the ports do not fully open for admission , this not unusual , don't forget these are the exaust ports aswell
If you are really desperate to learn about valve gear I can recomend
"Stephenson's Valve Gear" by D L Ashton it might take a bit of finding but well worth the effort, my copy is dated 1976 or originally sold by M.A.P. publications
I have built many marine compound engines and have always designed my valve s with lead at TDC. The amount of lead is determined by the stroke of the piston. There is always that flat spot at the top and bottom of the stroke that very little piston movement accrued. This is the beginning of the point of lead. The more lead the more the valve is opened at TDC and just after. Herreshoff used 10 to 12% of stroke for lead on the HP and as much as 30% on LP cylinders, it all depends on the length of stroke.
Car engines tend to be chocked off by the size of the pipe from the boiler to the engine. My Stanley only had a ½ IPS to the engine. My boat has a 1-1/2 inch pipe. The Stanley boiler runs with about 550PSI and at normal cursing around 100- to 125 at the cylinder.
My boat ran with 275PSI in the boiler and 275 at the HP cylinder. If I wanted to run slower I would link back the valve gear not the throttle, unless coming to a stop.
Posted by: les nelson (---.dynamic.dsl.as9105.com)
Date: January 9, 2009 02:57PM
I have just been to "Blackgates Engineering" (can be found on the web) they stock Don Ashtons book "Walschearts and Stephensons Valve gear" @ about £15 they do a postal service, so if you really want to know about valve gears this should "do the trick" Happy new year to all and keep on steaming Les