Heisler Engine Design Part VII 
Tumbling Arm Linkages
Nelson Riedel, Nelson@NelsonsLocomotive.com
11/15/2004, last updated 12/06/2005

The photo above shows the upper part of the valve linkage on MRSR 91.  The eccentrics and associated straps and links are off the bottom of the photo.   The modeling of the tumbling arm, link hanger, link saddle and tumbling arm lever are described in this page.  The remaining parts of the valve linkage are described in the Heisler Engine Part VIII page.   

This side view of the lower part of the rocker arm base shows how the tumbling lever and tumbling arm are supported.  Recall that the rocker arm base was described Part VI

Tumbling Arm:  The initial plan was to make a casting of the tumbling arm. However, it seems fairly easy to fabricate from steel plate and rods and only one is required so it was decided that it's not worth the effort to make a mold. 

Rverse Link Hanger: This drawing shows the reverse link hanger.  It, like the rocker arm, will be cast in iron or steel with a minimum of machining required such as reaming the holes for the shafts and bearings. Standard bronze flanged sleeve bearings will be pressed into the cylinders.
This is the reversing link hanger pattern made from brass bar and rods silver soldered together.  Soft solder was used to make small fillets.

Reversing Link Saddle: The link saddle attaches the reversing link to the link hanger.  The link hanger in turn attaches to the tumbling arm which controls the link setting  to forward, reverse or neutral.  The link saddle will be machined from mild steel.  The pin part will be silver soldered into a hole in the flat part.

The drawing above shows the relationship of the tumbling arm, link hanger, saddle and reversing link.  The tumbling arm is rotated to move the link between the neutral,  forward and reverse positions.

The drawing above shows the top view of the upper valve linkages. The pins and sleeve bearings are shown in cross section to clarify how everything fits together.  (The drawing is not completely accurate in that the rocker arm, link hanger, reversing link and valve stem head  have been positioned horizontally to simplify constructing the drawing.  In an accurate drawing the four pieces would appear shorter.)             

Reversing Linkage: The photo above shows the linkage between the tumbling arm and the reversing lever in the cab on Cass 6.  This photo was taken when the crankshaft was out of Cass 6.  The linkage on MRSR 91 appears to be the same. The photo on right shows the linkage pivot under the right cylinder.      The photo below shows the front part of the reversing linkage where it connects to the tumbling lever.

Ball Joints:  McMaster-Carr carries the ball joints pictured on the right; number 6072K81 with 10-32 studs and shanks appears to be  a good choice for the Heisler reverse linkage. The shanks are available with either RH or LH threads.  Pairing  LH and RH units with a threaded link between will make a good substitute for the ball joints and link pictured above.   The linkage from the Tumbling Arm Lever to the cab including these ball joins will be designed later.

Tumbling Lever:   The initial plan was to also cast the tumbling arm lever.  However, after considering the effort required to make the mold I decided to fabricate the first one from bar stock.   

The drawing above shows how the tumbling lever (red) is positioned relative to the other parts of the upper valve linkages.     The red lever is shown in three positions.  The central position at 55 degrees with the vertical is the neutral position.  The  approximate 20 degree rotation required to move from neutral to full gear is represented by the other two positions.   The drawing shows that there is some clearance with the valve stem head in the upper position and with the main bearing in the lower position.        

The drawing above shows the tumbling lever added to earlier drawings of the upper valve linkage.  Part of the rocker arm base that supports the right cylinder rocker arm (left side of drawing) has been removed  to show a clearer view of the connection between the tumbling lever and tumbling arm.  The shaft connecting the arm with the lever as well as the flanged sleeve bearings around the shaft are shown in cross section to clarify how the pieces fit together.

The remaining parts of the reversing linkage between the tumbling arm lever and the reversing lever in the cab will be designed after the engine is mounted to the frame.   

This finishes the upper part of the valve linkage.  The lower part of the linkage consisting of the eccentric straps and eccentric rods will be described in the next part.