Cass 6 Engine Part V 
 Eccentrics Straps, Rods and Links
Nelson Riedel, Nelson@NelsonsLocomotive.com
6/26/2004, last updated 04/08/2006

 

Eccentric Straps:   We start this last part of the valves with the eccentric straps.  We were lucky to find a spare strap so the measuring and photographing was much easier.  

That is a bearing inside the casting--- maybe babbitt metal. 

Two rods fasten to the top of the strap, one connecting to each reversing link.   The left rod that is fastened with three bolts is fixed (but can be adjusted).   The right rod that is fastened with a pin is the the pivoting rod.  The orientation of the strap in the photo of the front eccentric strap used for engine reverse.  The back strap is reversed left to right with the fixed strap on the right.  The back strap is used for engine forward  
This photo shows a couple very dirty eccentric rods. The rod closest to the camera is a fixed rod and the one further away is a pivoting rod. 

The reversing links  front to back  position is such that they are centered on the joint between the two eccentrics. The forked ends of the rods are offset so that the center of the fork is also aligned with the joint between the two eccentrics.  This symmetry allows one design to be used for both sets of straps and rods.   

 

The drawing below shows the eccentric straps and rods.

 

Reversing Link:  The reversing link was hard to photograph because it is partially hidden by the other valve parts.  This photo show the outside half of the left reversing link.  The reversing link block slides in the the slot in the reversing link.  The pin through the center of the reversing link block connects to the rocker arm and valve stem head.  When the eccentric rod moves the reversing link up and down the motion is coupled via the reversing link block  and rocker arm to the valve stem and on to the valve. 

The reversing link is connected to the link hanger via the reversing link saddle. There is clearance under the reversing link saddle for the reversing link block to move along the slot in the reversing link.  
This shows a top view of the right reversing link  with the valve stem head to the rear of the reversing link.  
Drawing of the reversing link.
Drawing of the reversing link block.   It appears that the block and block back are fastened together with rivets.  I'll probably use flat head screws on the model.  
Drawing of the reversing link saddle.  It appears that the saddle is attached to the link with rivets.   I'll probably use flat head screws on the model. 
Reversing Link Hanger:  The reversing link hangers are the only valve components that are easy to photograph and measure ---they sort of hang at the top of the pile. 

The reversing link hanger connects the tumbling arm to the reversing link.  When the tumbling arm rotates, the revering link is forced to slide along the link bock.  As the reversing link moves, the fixed eccentric rod forces  the associated eccentric strap to rotate on the eccentric.  At the extremes of the tumbling arm rotation, one of the eccentric rods is directly under the valve stem head and the engine is set for forward or reverse.  When the tumbling arm is in the middle of it's rotation the valve stem head is positioned in the middle of the reversing link, midway between to two eccentric rods and there will be no valve stem movement.       
This drawing shows that even this simple link is not quite as simple as one might expect.  One can speculate as to why the hanger isn't symmetrical.    Recall that they didn't have CAD systems back then so maybe they made all the other valve parts and put them together and then designed this last part so that everything would connect.   (That technique will likely be used on the model.)   
Tumbling Arm: The tumbling arms for the two cylinders are combined into a single casting as shown in this photo. 
Drawing of the tumbling arm.
Tumbling Lever:  The tumbling lever is connected to the tumbling arm via a shaft through the lower part of the rocker arm base.  The tumbling lever is linked to the reversing lever in the cab.    I was unable to get a respectable photo of the Cass 6 tumbling lever so I took this photo of a partially disassembled smaller Heisler engine where the lever is visible.     
This drawing shows the dimensions of the Cass 6 lever.  The lever is positioned to the front of the crankcase and to the rear of the eccentrics. 

The sketch above shows the valve linkage positions when the reversing lever is in the neutral position.     

Recall that there are two valve adjustments , the valve stem head can be moved on the valve stem (two nuts)  and the fixed eccentric rod can be moved relative to the eccentric strap (slotted holes in the rod secured by 3 bolts)   The Cass shop foreman Artie Barkley told me how to do the adjustment so best document it here before I forget it.  The reversing lever is set to the position that puts the upper end of a  pivoting eccentric rod in line with the valve stem.    The piston is moved to top dead center and the valve stem head is then adjusted (two nuts on stem)  for the desired valve lead.  The second valve stem head  is adjusted before adjusting the fixed eccentric rods.  Next, the reversing lever is set so that the upper end of a fixed eccentric rod is in line with the valve stem and the piston moved to top dead center.  The three bolts holding the rod to the eccentric strap are loosened and the rod moved to the position that gives the desired valve lead. The second fixed eccentric rod is then adjusted using the same procedure.         

This wraps up the Cass 6 Engine --- finally.  The Engine drawing can be downloaded from the Drawings page.

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