Timing - Full port @ half stroke

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johnpenn74
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Timing - Full port @ half stroke

Post by johnpenn74 »

Fellow Live Steamers,

During what conditions are engines timed for full port @ half stroke?

Backstory -
During a recent work visit to the Pacfic Northwest I had the privaledge of Visiting Dons show and seening his beautiful Wilamette 2 speed Yarder. See pictures below. During the course of discussion I was told it was timed for forward only Full port at half stroke of the cylinder. IE the eccentric was 90 to the crank. Hmm ok..

Further investigation of other stationary engines from online videos said the same thing. Set the eccentric to 90. Full port @ half stroke.

Last but not least, while working with Charlie on his locomotive timing (an english design of a baldwin) it was also found that the eccentrics were set at 90. Full port @ half stroke.

When I timed my Allen ten wheeler, I calculated the number to crack open the port just when the main cylinder was at the beginning of stroke (IE no lead). The advance was something like 23 degrees.

So why are these two setting so different?

But wait there's more. I pulled some drawings of modern Walkshherts enginers looking at the crank and both appear to be at 90 degrees. What?? See below I would like to hear some opinions.

JP
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Don Donkey wil 2speed small.png
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valve gear drawings crank small.png
valve gear drawings crank small.png (1.41 MiB) Viewed 1455 times
John Pennington

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Charles T. McCullough
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Re: Timing - Full port @ half stroke

Post by Charles T. McCullough »

The eccentric is set to 90-deg and you play with the timing by "notching up" via the "valve gear" (Walshaerts, Southern, Baker, etc. [but NOT Stephenson and a couple of others!]). If you play with the crank angle, then you cannot get similar settings in forward AND reverse.
.
[Stephenson's, and a couple of others use two eccentrics, one for forward and one for reverse and you shift between them with the valve gear. and you can alter the angle of one or both to your heart's content to adjust the timing for best operating in either direction.]
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Fender
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Re: Timing - Full port @ half stroke

Post by Fender »

The reason Charlie’s engine was so off was because there was so much slop in the Stephenson valve gear parts when he bought the engine. Doesn’t seem to be a problem with the design, just poorly made parts. He is going through the valve gear making new bushings and pins, and even soldered a shim onto the link blocks to make a better fit in the links. It should run a lot better when he finishes.
I think the reason for the odd valve events on the yarder/donkey is that it is designed for maximum power at slow speeds, not limited cutoff for efficiency at higher speeds.
Dan Watson
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Dick_Morris
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Re: Timing - Full port @ half stroke

Post by Dick_Morris »

My impression on donkeys and capstans is that late cutoff would be the norm as high power is needed in short bursts. Because of their intermittent use the wasted steam isn't a major consideration.
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Bill Shields
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Re: Timing - Full port @ half stroke

Post by Bill Shields »

Dick_Morris wrote: Mon Feb 27, 2023 12:12 am My impression on donkeys and capstans is that late cutoff would be the norm as high power is needed in short bursts. Because of their intermittent use the wasted steam isn't a major consideration.
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