Cass 6 Engine Part III
Cylinders, Heads, Pistons, & Rods
Nelson Riedel, Nelson@NelsonsLocomotive.com
6/24/2004, last updated 04/08/2006

In this part we look at the cylinders, heads, pistons, rods.

Cylinders:  This photo shows the right cylinder.  The cylinder and steam chest is a single casting.  Recall that the right cylinder- steam chest is 7" longer front-to-back than the left cylinder-steam chest.  Also observe that the steam chest is tapered slightly back to front. Those are cylinder cocks with an operating link directly under the cylinder.  The valve in the lower part of the steam chest serves the same function as the cylinder cocks --- to drain off condensate.   That is a snifter valve in the upper front of the steam chest. 

The upper head has been installed but the head nuts haven't been installed.  The head cover has not been installed either.  The cover over the front of the steam chest has been installed.  
This later photo of the right cylinder shows the steam input at the upper edge of the steam chest.  The exhaust exits the steam chest horizontally on the boiler side and then bends toward the front.   An offset fitting brings the exhaust pipe lower and toward the boiler so that it can pass inside of  the upper frame bar.     
This is the left cylinder which is shorter front-to-back than the right side.  The cylinder cocks, steam chest drain valve and steam chest cover haven't been installed yet.     

The heads have an unusual shape with a recess near the outer edge and then an upward bulge near the middle.  The shape matches the top of the piston.  Why is the piston that shape?  I made a guess, read on ....... 
This is the left cylinder fully assembled with head cover in place. The locomotive is building steam with cylinder cocks and steam chest drain valve open.   

The drawing below shows the outside dimensions of the left cylinder with steam chest and steam chest cover and jacket in place.   The right side is the same except that the steam chest is 7" longer front to back

I've been unable to find a disassembled cylinder and steam chest so there are no drawings of the internal structure.     

 

Upper Engine Mount: There is an upper engine mount that connects between the cylinder and the upper frame bar.   The mount is difficult to photograph because it's high and on the inside of the cylinder and hidden by the walkway.  

This photo shows the inside of the right mount with 2 bolts into the cylinder on the lower side and 4 bolts through the  frame bar and the top of the mount that is above the frame bar.  . 
This shows the rear edge of the right mount.  The upper part of the mount is angle shaped mating with the top and out side edges of the frame bar.
This is the best I could I could do to show the upper side of the mount.  There are two ribs on the upper side.  There are 3 bolts through the upper side into the cylinder.  
This drawing shows several views of the mount.  The dimensions are close but may be off slightly. 

 

Piston: I was fortunate to find a spare piston to photograph and measure.  The top side has a slight recess near the outer edge and then bulges upward.   The inside of the extension in the center is tapered to mate with the piston rod.  The end of the rod is threaded for a nut to hold the rod and piston together. 

 The threads on the outside of the extension are for a tool to force the rod out of the piston (the rod with crosshead must come out the bottom of the cylinder and the piston out the top of the cylinder.)          
This shows that the inside of the piston is recessed to a depth of 5" measured from the lower edge. 

There are two rings on the piston
This photo was taken looking up along the piston rod to the bottom side  of the lower head. The lower head is recessed and the packing gland is above the lower edge of the head ---- essentially inside of the cylinder.

It is my guess that the packing gland was moved inside the cylinder to keep the crosshead guides as short as possible and to limit the distance the cylinders stick out from the locomotive.  That resulting bulge on the upper side of the lower head necessitated that the piston and upper head have a matching  bulges up.    

 

 

The overall dimensions on the above drawing are fairly accurate.  However, the detailed shape of the heads are a guess.   The bottom side of the lower head will likely have a ridge of some kind to keep it centered on the crosshead guide.  

Crosshead & Piston Rod: The crosshead and piston rod are a single piece.   This photo shows the left crosshead of a partially disassembled engine.  That is a two piece sleeve bearing is the middle of the crosshead. There are also bearings (bronze strips)  between the crosshead and the crosshead guide.  
This is the right crosshead of the same engine as the photo above.   The part above the bearing (probably a wedge tightening device) is missing on this side 

The wedges and associated bolts that tighten against the side bearings are clearly visible here. 

The drawing below shows the overall dimensions of the piston - rod - crosshead combination.  The model crosshead will likely be made on a piece of bronze so no effort was made to detail the sleeve bearing in the middle or the sliding bearings on the outer edges.

 

 

 

Connecting Rod: I wasn't fortunate enough to find a spare connecting rod so I had to measure the ends and speculate on what's between the ends.   This photo shows the lower end. The configuration is similar to the shays with the bearing held to the rod by a strap.  

 
The lower end of the strap has extra bulk to hold an adjustment screw.   A steel plate is visible between the upper edge of the strap bottom and the lower edge of the bearing flange.   I assume the adjustment screw is tightened to push the two halves of the bearing together  
That cylinder sticking out the side of the strap I assume is an oil cup of sorts.  The two bolts that hold the strap to the rod are visible on the rod on the left side of the photo.  ( This photo was taken from the left side of the locomotive.) 
This is the upper end of the rod where it fastens to the crosshead.  The rod end is shaped like a clevis with a large bolt connecting the clevis and crosshead.

 

The drawings below show the dimensions of the rod, strap and bearing. 

 

 

This wraps up the piston - cylinder -crankshaft part of the engine.  The drawings for this part of the engine can be downloaded from  the Drawings section.   We start on the valves in Part IV. 

 

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