Valve Motion Assembly & Timing
Procedures U.S.R.A.  2-8-2


The following procedures are intended to help the builder in assembling and timing
the valve gear on the U.S.R.A 2-8-2.  These procedures may be followed verbatim or modified to suit the
techniques, methods and experience of the builder.  It is advisable to read through the valve motion
assembly and timing instructions as many times as necessary in order to gain the best understanding of
the procedures involved.  The valve motion assembly can be tricky so don’t try to work too rapidly.

I.  VALVE MOTION ASSEMBLY

    1.  Machine rods, levers and links per print, and test fit bolts and pins in appropriate holes.  
    Drill thru captive pins (roll pinned) and mark the ends of the pins and rods for alignment.  Polish
    pins and bolts if too tight for bushings and holes.  Pins and bolts should be snug but allow for
    rotation of rods without binding.

    2.  Valve Motion Erection

        A.  Lay our parts for right (engineers) side of engine.
        NOTE:  It is advisable to assemble the valve motion for one side of
        the locomotive at a time to avoid mixing of left and right hand rods and levers.

        B.  Assemble and pin radius rods/combination lever assemblies
        per assembly drawing X-2083

        C.  Assemble and pin radius rod/combination lever assemblies
        to valve crossheads and install resulting assemblies on locomotive.        

        D.  Assemble union links to crosshead wrist pins, then assemble
        and pin union links to combination levers.

        E.  Disassemble expansion link assemblies.
        NOTE:  Expansion links should be reassembled in the same order
        as they were disassembled.

        F.  Assemble expansion links, link blocks, and link block pins to radius
        rods per view A-A, drawing X-2083.

        G.  Install link trunnions in link supports, then rotate expansion link/link block/raduis rod
        assemblies into position with link trunnions, re-pin expansion link assemblies and bolt
        assemblies together.
    
        H.  Install tumbling shaft, making sure shaft can move without binding.  Bolt lifting links
              to tumbling shaft arms and radius rod ends.
    
        I.  Temporarily install eccentric cranks on main crankpins, but do not tighten bolts at this
             time.

        J.  Assemble eccentric rods to eccentric cranks, then assemble and bolt eccentric rods to
             expansion links.    

II.  VALVE MOTION TIMING PROCEDURE

    1.  With motion structure & rods assembled to chassis, set locomotive ride height by blocking
          between driver journal boxes and pedestal binders.  Block the engine such that the distance
          from the top of the sideframe to the top of the railhead is 6 3/4 inches.

    2.  Establish the front and back dead center positions of the cylinder piston travel.
         Definition:  The locomotive is said to be on a dead center at the precise moment of maximum
         Cylinder piston travel, either front or back from the cylinder centerline.

        A.  Make a scribing tram as shown on the page of illustrations with these procedures.

        B.  Using the tram, scribe the main driver wheel rims from the centerdrilled hole in the
              axle end.

        C.  Centerpunch the brake hanger clevis pins on the main drive wheel brake hangers.
              Try to center the punch mark as much as possible to reduce any chance of error due to
              the pin rotation.  If the punch mark is off center, scribe a witness mark on the clevis
              pin head and brake hanger for alignment.  This punch mark will be used to locate the
              dead centers for all timing events and will be useful in retiming the valve motion at a
               later date.
        
        D.  Starting with one side of the locomotive, rotate the drivers until maximum forward
              Crosshead travel is achieved.  Measure the distance from the crosshead to the rear
              cylinder head and make a spacer block slightly longer than the measured distance,
              1/8 inch longer would be appropriate.  (see illustration below)

        E.  Rotate the drivers until the spacer block can be inserted between the crosshead and
             rear cylinder head then rotate the drivers forward until the spacer is contacted by the
             crosshead and cylinder head.  Without moving anything, scribe an arc on the main
             driver with the tram using the punch mark on the brake hanger clevis pin as the center
             of the arc.

        F.  Remove the spacer block and rotate the drivers to the other side of dead center.
              Reinsert the spacer block and repeat procedure (E).  Locate the exact midpoint
             between the two tram marks on the main driver and place a sharp punch mark
               at this point.  This punch mark locates the exact forward dead center when the tram
              contacts this punch mark and the punch mark on the brake hanger clevis pin.


        G.     To find the back dead center position, rotate the drivers until maximum reverse
            crosshead travel is achieved.  Measure the distance from the crosshead to the rear
            Cylinder head and make a spacer block slightly shorter than the measured
            distance, 1/8 inch shorter would be appropriate.  (see illustration below)

        H.    Repeat procedures E and F in the reverse direction to locate back dead center.

    3.      To position the cylinder pistons, place the chassis in forward dead center position.  With
        the front cylinder heads removed, thread the piston/piston rod assembly into the
        crosshead until there us a 3/8 inch gap between the piston and the cylinder face.
        The piston rod assemblies may now be locked in place and the front cylinder heads
        reinstalled.  Do this procedure for both sides of the locomotive.

    4.    Find the top and bottom dead center positions of the valve motion for each side of the
        locomotive.  
    
        A.    Set the chassis in forward dead center positions and make a witness mark on the
            crosshead and a corresponding mark on the crosshead guide.

        B.      Set the chassis in back dead center position and make a matching alignment
            mark on the crosshead guide.

        C.      Measure half way between the two alignment marks and make a mark on the
            on the crosshead guide, this mark is the top and bottom dead center position.
            By aligning the witness mark on the crosshead and the top and bottom dead
            center mark, the chassis will be in mid-position and the valve position may be set.

    5.      To set the position of the piston valves, place the chassis in mid-position (top and bottom
        dead center).

        A.      Set the valve motion in mid gear position.  Mid gear is when the link block pin
            and link trunnion pins are on the same centerline, and can be checked by rocking
            the expansion link and moving the radius rod until no motion is imparted to the
            valve crosshead with the chassis in mid-position (top and bottom dead center).

        B.       Remove the front valve heads and pipe plugs in the valve chest admission ports.
            Thread the valve stem into the valve crosshead until the valve is centered and the
            valve rings are positioned equally when viewed through the valve chest admission
            ports.

        C.      Move the chassis to the forward dead center and not the position of the ring and
            port clearance.   Repeat the procedure for back dead center and note the position
            of the ring and port clearance.  Adjust the valve stem until the two openings
            are the same.  the valve stem may now be locked in place.   Reinstall the front
            valve heads and plugs.
       
    6.      To set the eccentric cranks, locate the eccentric cranks approximately as shown on
        drawing X-2083 and temporarily tighten the clamp belts.   NOTE:  Set the drive wheels
        in the same position (bottom dead center) for each side of the chassis with the eccentric
        crank set towards the cylinders.

        A.      With the valve motion in mid gear position (procedure 5-A), roll the chassis
            to forward dead center and measure from any convenient stationary reference point
            to the eccentric rod/expansion link pivot bolt.

        B.      Roll the chassis to back dead center position and measure from the same     
            stationary reference point to the eccentric rod/expansion link pivot bolt.

        C.      Adjust the eccentric crank throw until the reference measurements are the same
            and lock the eccentric crank pin position.

        D.     Place a witness (scribe) mark on the crankpin and eccentric crank for future
            reference and ease of re-alignment.

    III.   SETTING REVERSE STAND LINKAGE AND REVERSE STAND

    1.     After installation of boiler, boiler accessories and cab, the reverse stand and linkage may
        be set.    

        A.      With the valve motion in mid gear (procedure 5-A), place the Johnson bar in
            the mid notch position.  The mid gear (notch) position is with the Johnson bar in a
            vertical position.  If the reverse stand quadrant has not been notched, do so at
            this time.

        B.      Measure and install the reverse linkage with the Johnson bar in mid gear and the
            valve motion in mid gear.


        C.    Move the Johnson bar toward forward, (full gear), while slowly rotating the
            engine drivers, as far as possible without causing the link blocks to hit the end of
            their slot at any point in the driver rotation.  This is the maximum cut-off     
            position for forward gear.  Mark where the latch is on the quadrant bars and file
            a notch for the latch.

        D.    Use the same procedure (C) in reverse to locate the maximum cut-off notch for
            reverse gear.    
        
        E.    After locating the full gear notches for each direction, the evenness of the timing
            should be checked.  This is done by setting the Johnson bar in one of the full
            gear position and checking that the valves open and close at the same relative
            points in each of the four piston strokes (two on each side), then place the     
            johnson bar in the other full gear position and check the same information.  The
            two different directions (forward gear and reverse gear) may not be exactly the
            same, however, both sides of the engine have to have equal events in forward
            (or reverse) direction.  If there are any discrepancies they may be due to the
            following causes:

            (1) Lifting levers on the tumbling shaft not of equal length or improperly
            aligned.
            (2) Lifting links not equal length
            (3) Radius of the expansion link slot and length of radius rod not equal
            (4) Location of lifting link connections to radius rods not equal
            (5) Locating of tumbling shaft bearing in relation to link trunnions not the same
            on both sides

        F.      After the valve events are adjusted to be correct in mid gear and both full gear
            positions, they will (except in unusual conditions) be correct in any position of the
            Johnson bar.  File intermediate notches to suit.
    
        G.      Install stops (a bolt will do) in the quadrants to prevent the Johnson bar from
            being moved beyond full gear position and to prevent accidental damage to the
            valve gear when in operation.

        
    IV.    CONCLUSION:  If the aforementioned procedures are completed properly, the     
        locomotive should run square on steam when loaded to normal ride height and weight.  
        NOTE:  If weight is added or removed from the locomotive, valve motion retiming may
        be necessary for proper operation.

A-2088 DRAWING ILLUSTRATION


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