Timing Stevenson Valve Gear can be a real challange, especially when you do it the first time. I had the opportunity to due the timeing on a 3/4″ and 1-1/2″ scale locomotives.

First, you want to set the cams. The cams consist 4 individual cams.

Right hand side of drive wheel:
drive   cam-01 Forward –>
Left hand side drive wheel:
<— Forward cam-02 drive

Next, you will do Slide Valve and Cylinder Adjustments.

1.) At rear dead center, both steam ports are closed by the slide valve

cyl-01  drive-02  drive-02


2.) With the crank pin a few degrees past read dead center, the slide valve begins to open the rear steam port, for the admission of fresh steam, and the front port, for the ejection of used steam through the exhaust port.

cyl-02 drive-04 drive-04


3.) With the crankpin at apporximately 150 – 160 degrees of rotation, the slide valve should close the rear steam port. The rest of the rotation, through the foward dead center, is performed with the help of steam expansion.

cyl-03 drive-05 drive-05


4.) The slide valve closes both steam ports as in 1.

cyl-04 drive-03  drive-03



Timing Stevenson Valve Gear — 7 Comments

  1. Attn: Admin.
    Iam trying to view the article timing Stevenson Valve Gear it reads well
    but I cannot view the essential Images.Iwas wondering if they could be
    emailed.This would be most appreciated.

    Many Thanks
    Russ Bonser.

  2. 8-31-12 10:55 p.m. CDT
    I have a Stephenson setup with no manual and saw your setup but none of the drawings or pictures show on the screen. Just blank with a red X in the left corner. I really need to set it up to operate smoothly but can only find vague instructions. The drivers set on a 7.5″ width track.
    Please advise on how to get the pictures herein. Thank you kindly.

  3. Your illustration notes
    4 cams. My loco has 2 reverse cams inside
    and 2 forward cams outside.
    How do the reverse cams enter into the illustration ?

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