Heisler Engine Design Part II
Crankcase & Crosshead Guides
Nelson Riedel, Nelson@NelsonsLocomotive.com
10/6/2004, last updated 09/12/2009

Diamond Frame:  The diamond frame cross section dimensions were fixed before starting on the crankcase.  The inside distance between the frame sides on Cass 6 is 62" which scales to 8.3".  I want as much room possible for the boiler so the inside spacing was increased to 8.5".  That will permit a boiler diameter of 7.5" with 0.25" insulation and a thin jacket.  The frame bars scale to 0.536" which was increased to 9/16" square bar stock.

Crankcase & Crosshead Guides:   Recall that Heisler split the crankcase front-to-back and combined a crosshead guide with each crankcase half.  The initial plan was to cast the crankcase as one piece and the crosshead guides separate castings.  The crankcase turned out to be too large to cast using the envisioned investment casting techniques so it was split into two pieces.   The half crankcase pattern made for investment casting was later incorporated into a sand casting pattern.   The crankcase is made by bolting two halves together.  The front has some areas machined off for the rocker arm base and also to provide clearance  for the end of the rocker arms.   The crosshead guides are machined separately and then attached to the crankcase with screws.  The joints between the crosshead guides and the crankcase are filled with an epoxy material and smoothed to resemble the fillets found on the prototype castings.     The next three drawings show the overall dimensions of the combined crankcase and crosshead guides.  These drawings incorporate the decisions on the crankshaft from the  Engine Design I page and the frame dimensions above.

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Crankcase:  The next three drawings show the crankcase. Two identical crankcase half castings are bolted together with 6-32 screws to make the crankcase.   The castings are cast iron. As noted on the adjacent drawing, the recesses on the upper side of the front  provide clearance for the rocker arms and the flanges are cut off the front to make a flat area to mount the rocker arm base,
The holes for the main bearing cap are located using the bearing cap as a guide. The holes for the main bearings are drilled/bored after the bearing caps have been attached.
The castings come without the holes for the crosshead guides.  These holes are drilled/bored after the  two halve have been mated together.

The photo above shows the a pair of crankcase castings that have been joined, the bearing caps attached and the combination bored for the main bearings.  The bearings together with the crankshaft have been installed to verify the fit.   The holes have also been bored for the crosshead guides.    The top and front have been partially machined for the rocker arm base.    

Crosshead Guide:  The drawing above shows the right side crosshead guide.  The left side is identical except for the access slot in the side.  Both guides have the slot in the front and a round opening in the back.  The little box on the upper side is for lubrication.  The cylinder is machined from cast iron.  The mild steel fin and little bock are screwed to the cylindrical part and then silver soldered in place.    The fin is cut  to match the crankcase.   A 3/16"  wide slot will be milled in both the cylindrical part and the crankcase to position the fin.   

 The initial plan was to solder or braze the crosshead guide to the crankcase.  However, the current thought is to run screws through that crankcase into crosshead guide,   An additional couple screws will  be through the crankcase up into shark fin.         

Lower Engine Mount Bracket: There are one of these brackets on each side.  They clamp the 9/16" square lower frame bars to the sides of the crankcase.  Fourteen of the holes (those closest to the edges) match up with threaded holes in the crankcase.  The other four match up with vertical holes up the frame bar and the crankcase.   These four have screws with heads on the bottom and nuts on the top.   The brackets are aligned with the crosshead guide centerlines.   The brackets will be used as guides to drill the mating holes in the crankcase. The brackets will be made from 3/16" thick HRS  angle.

The cylinders and heads are designed next in Engine Design III.