Stephenson Slide Valves

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flyguy
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Stephenson Slide Valves

Post by flyguy » Sun Jan 07, 2018 1:49 am

Hi Everyone,

I have been working on fine tuning the timing on my Allen Ten Wheeler. I set the valves using the technique described in the Allen drawings. I have run into one small issue though. I cannot even out the valve travel across the ports on the right side of the engine.

I started out by finding accurate dead centers using a dial indicator. Using a tram I set the engine on front dead center then set the eccentrics to approximately 22 degrees by eye. I set the length of the eccentric rods to the dimensions on the drawing using a height gage. I checked the total valve travel and set it to the drawings (.625).

Now the problem. I cannot get even valve travel on the right side of the engine. The valve uncovers the rear port more than it uncovers the front port. When I try to fix this issue by adjusting the valve on the valve stem, I end up with the part which mates the valve rod to the valve stem bottoming out on the gland nut on the valve chest. In short I need to decrease the effective length of the valve rod without causing it to bottom out or interfere with the gland nut.

In the attached photo, it is the larger steel hex nut on the front of the valve stem which is interfering with the brass gland nut.

I did not have this issue with the left side of the engine, the valve travel is even across both ports.

Let me know if you guys have any ideas.

Thanks,

James
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James Powell
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Joined: Fri Oct 28, 2011 10:42 pm

Re: Stephenson Slide Valves

Post by James Powell » Sun Jan 07, 2018 2:47 am

Take the gland nut out, thin it in the lathe, put it back. I'm assuming you are looking for less than 25 thou more clearance (one turn on 40 TPI thread). Otherwise, the other bit there could have a nibble taken off of it (the connecting nut) . Worst comes to worst, make a new valve rod that is longer, and make the mating part shorter. (that's if there is a lot of difference between the two, and not a lot of thread left to play with).

Why is this a problem on your engine? Could be many things- but remaking parts to make an engine "work" is not at all uncommon. You think you are 7/8ths done...well, the job is more like 1/2 done to get the best performance out of your engine !. Plumbing them, and making them work well is a bit of a specialized art form even in full size. What you want is not a regular fitter, but a super fitter.

James

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Bill Shields
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Re: Stephenson Slide Valves

Post by Bill Shields » Sun Jan 07, 2018 7:46 am

If you want an extensive treatise on setting Stephen valves, written by Fred Colvin, let me have your e-mail address and I will send it to you. Sure, it's 100+ years old but forth every electron.

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Marty_Knox
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Re: Stephenson Slide Valves

Post by Marty_Knox » Sun Jan 07, 2018 8:29 am

On the Allen locomotives the link is suspended from the wrong place. The pin should be located close to the back of the slot in the link.

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Bill Shields
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Re: Stephenson Slide Valves

Post by Bill Shields » Sun Jan 07, 2018 9:29 am

I can supply a drawing of how it should be set. This does not alter settings at full gear.

blff cty lcmtv wrks
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Re: Stephenson Slide Valves

Post by blff cty lcmtv wrks » Sun Jan 07, 2018 5:49 pm

marty as ricky r would say "essplain".
big c

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Marty_Knox
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Re: Stephenson Slide Valves

Post by Marty_Knox » Mon Jan 08, 2018 9:36 am

blff cty lcmtv wrks wrote:
Sun Jan 07, 2018 5:49 pm
marty as ricky r would say "essplain".
big c
The following illustration is from the chapter on The Stephenson Valve Gear in the the Steam Locomotive Study Course. It explains the back set needed, and why it is needed.
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Bill Shields
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Re: Stephenson Slide Valves

Post by Bill Shields » Mon Jan 08, 2018 9:56 am

As I previously stated, if you want a drawing, send me your direct e-mail and I will be happy to send you a copy.

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