Heisler Engine Construction Part IV
Crankcase, Crosshead Guide & Bearing Cap

Nelson Riedel, Nelson@NelsonsLocomotive.com
9/14/2009, last updated 09/16/2009

Crankcase HC-100: The crankcase castings were waiting for me when I returned from a 5 week trip in July.  The first patterns were made over 3 years before so it's been a a long wait. I was so anxious to get at the machining I forgot to take any photos of the plain castings.


The crankcase design information is on the  Engine Design II page

The pattern maker had to add some draft to the joint between the two halves so the draft has to be machined off that surface.   I shimmed the part of the casting under the clamps in the photo to compensate for the draft and then took small cuts to smooth the surfaces that mate with frame bar to make a reference surface.

The amount of draft can be determined by measuring the width of the flange --- it is wider near the bottom..  

The next step was to flip the casting over, use the reference surface just created and machine off the draft on the joint between the castings.

The casting is really hanging out there so fine cuts were the order of the day.


The top of the joint flange between the castings was smoothed with a file to eliminate any high spots. The setup at the right was then used to machine the surface where the main bearing cap mates with the crankcase.  

Once the joint between the castings and the surface that mates with the bearing cap were squared, the surfaces that mate with the frame bar were squared again.  This gets four  reference surfaces on each casting.  

The next step was to make the hole for the crosshead guide.   I used the inexpensive adjustable vise that came with the mill to hold the casting at a 45 degree angle.  The vice jaws had to be removed to accommodate the casting.

Recall that the crosshead guide is 15/32" off center such that there is 15/16" between the two crosshead guide center lines.  This is the most critical measurement.

The holes were started with a 1/4" drill and several larger drills were then used, the largest 1 1/4".   



The next step was to enlarge the hole using the boring head.  Small cuts, about 0.03" at a time were taken.  Once the boring bar is cutting into the flat vertical surface, it is possible to verify all the measurements as well as the angle.  It is possible to make small adjustments at that time before finishing the boring.



The two casting were joined together next.  The screw holes were drilled in one half and that half was then used as a pattern to drill the holes in the other half. 


The casting pair is secured in this position so that the flange in the top half of the front and the front half of the top can be be cut off and milled flat.  Note that there are no screws in the front half of the top and the top half of the front.

The piece is resting on a couple aluminum blocks which substitute for the frame bars.      


The next step was to make the main bearing caps (HM104 - Engine Design 1) and attach the caps to the casting pair with 6-32 SHCS.  The screw heads are recessed on the bottom so that the bottom surface is flat.  (These screws will be later replaced with 10-32 screws.)    

The setup shown on the right was used to bore the hole for the main bearing in the crankcase castings and the bearing cap.


Another view of boring the hole for the bearing.  

The setup on the right was used to turn the shoulder on the bearing cap.  The edges of the bearing cap will be rounded so that it to resembles a casting.    


 The nearly finished crankcase with bearing caps and crankshaft is shown above.  



Crosshead Guides (HM 105): The crosshead guides were tuned  from cast iron bar stock using a procedure similar to that used to make the cylinder bushings.  The photo shows boring the inside of the guide.

The two guides are identical except for the openings in the sides.  Both guides have a slot in the front side and a round  hole on the back side.

The 1 1/4" diameter hole for the rear side was drilled first and then then the crosshead guided was rotated and two 1 1/4" holes for the front side were drilled.  The holes were initially drilled  1/4"  and then enlarged with several intermediate drills before finishing with the 1 1/4" drill.  Doing the drilling in steps minimized the forces on the crosshead guide.

Note that the holes for the lower head screws have been drilled in the flange.  This helps with aligning the crosshead guide for this drilling operation. 

The material between the two holes on the front was cut out using an abrasive cutoff disk in a small rotary tool.   


The last step on the holes was to mill the sides of the slot even with the sides of the holes at each end as shown in the photo.  The result of this operation looked great. 

A caution, the edges  left by this milling operation were surprisingly sharp.  I smoothed them using a 1/2" sanding drum in the in the rotary tool.

This same setup was used to mill a 3/16" wide slot in the top of cylinder for the fin.  The slot is 15/32" off the crosshead guide centerline.  The orientation is reversed between the left and right sides such that both fins are on the crankcase centerline.   It is wise to verify the correct  location of the slot several times before making the cut (I was lucky). 



The crosshead guides fit really well in the crankcase casting.  I decided to attach the crosshead guide to the crank case with six 6-32 SHCS from the bottom.  The screws are oriented near the edge of the crosshead guide cylinder and the holes pierce the inside of the cylinder.  The holes are to the outside of the path of the cross head so as not to disrupt the bearing surface.

The crosshead flange must be aligned at the correct distance from the crankshaft and at the correct angle so that the cylinders are positioned properly,  A hole was tapped for a 6-32 screw along the crosshead guide centerline next to the edge of the opening in the crankcase.  The screw visible in the photo  is used to hold the crosshead  guide after it has been  positioned properly.


The photo above shows drilling one of the holes for the attachment screws. A tap drill was used for all six holes and then the crosshead guide was removed and the clearance drill and screw head counter bore were used on the crankcase.

The drawing at the right shows the locations of the 6 attachment screws from the crankcase into the crosshead guide.  The locations aren't critical except that the holes into the crosshead guide should be be outside  the crosshead path.

The drawing also shows two 2-56 screws through the fins, one into the cylinder and the other into the rectangular oil reserve.  This is to hold all the parts together when they are soldered.

The oil reserve is made from 9/16" rectangular bar left over from the frame.  A 7/16" hole was drilled in the end of the bar to make a cavity which will be packed with something to retain oil.  A 1/16" hole was drilled from the bottom of the reserve into cylinder --- the plan is for oil to slowly drip onto the crosshead-crosshead guide  bearing surface.   

A hole for a 4-40 SHCS was is also drilled through the crankcase into the fin to help secure the fin.

The fin is made from 3/16" plate and cut to fit.   Recall that a slot was milled in the crosshead guide to position the fin.  An adjoining slot was also milled in the top of the crankcase.  

After all the holes were drilled everything was  thoroughly cleaned and assembled the joints between the fin and crosshead guide,  fin and crankcase, and fin and oil reserve were fluxed and silver soldered.   A solder with the ability to fill a larger void was used since these joints were not very precise.

The photo on the right was taken right after the soldering operation.


After the soldering was completed, the crankcase halves were joined and the rocker arm base and rocker arms temporarily attached.   The places where the rocker arms hit the front of the crankcase were then identified and the interfering material was removed on the mill.   The photo shows this operation.  

The crosshead guide and the crankcase half were single castings on the prototype.  LPS Strong Steel Stick composite was used to make fillets between the crosshead guide and crankcase so that the assembly appears like a single casting.  

The photos above show the finished crankcase-crosshead units with the fillets made with the strong steel stick.  The cylinders are also attached so it really resembles the engine at this point.    After it was painted the composite fillets look like casting fillets.

Making the connecting  rod was next --- see Engine Construction V

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