Heisler Engine Construction Part VI
Finishing the Valve Linkages
Nelson Riedel, Nelson@NelsonsLocomotive.com
9/23/2009, last updated 09/24/2009

 The reversing link and eccentric straps are unusual shapes that I'd been dreading making so I put it off till the very end.   Putting them off gave time for thought of how best to the job.  In the end, the job was a snap. 

Reversing Link HM130:  The reversing link is described in the Engine Design VI page.

The critical part of the reversing link is the slot in which the link block moves.  This slot is at a 3.75" radius.  The sides of the slot must be smooth so that the link block will slide easily as the engine direction is changed.

Rotating the material past an end mill was selected as the easiest way to make the slot. 

The fixture shown in the photo was made to hold the reversing link while it was being machined.  The plate is 1/2" aluminum.  The hub was turned to be a snug fit in the rotary table center hole.  The 1/4" pin fits into a mating hole in the table.  This fixture can be removed and later replaced at essentially the same position on the table.  


This photo shows the fixture in use.  The first step was to locate the center rotary table at 0,0 on the digital readout.  The fixture was then attached as shown and the table rotated such that the long axis of the fixture was aligned with the left-to-right axis of the milling table.   This angle was noted as the center line of the fixture and later of the reversing link.   While the fixture was in this position the milling table was moved as required to locate and center drill two holes where the eccentric links attach to the reversing link.   The fixture was then removed, #3  holes drilled in the fixture and the fixture then used as a template to make matching holes in the reversing links.   The holes in the fixture were then tapped 1/4"-28 and the holes in the reversing links enlarged to 1/4".    
The photo above right shows the stacked reversing links secured to the fixture with a pair of 1/4-28 SHCS.  Additional holes were then center drilled in the reversing links for the link saddle attachment screws.  Holes were also drilled at the four corners of the slot in the reversing links.  These holes were all located using the X-Y indexing on the mill.      

The next step was to drill holes along the centerline of the slot as a first step to machining the slot.   This was done by rotating the rotary table.    

The reversing link shown here has a 2.5" long slot.  As noted in the design section, the slot length was revised to a length of 2".   

The next step was to machine the slot using an end mill.   The table was rotated under the end mill.  Small cuts --- 1/16" of an inch at a time were taken.  Once the slot was all the way though both reversing links, the milling table was moved along the left-to-right axis as necessary to finish the sides of the slot to the correct slot width.  

Cast iron left from the piece purchased for cylinder bushings was used for the revering link.  The disks were turned smooth and to the correct thickness on the lathe   

Photo on the right shows the finished slots. 

The next step was to locate and drill holes at the four places where there are fillets in the sides of the reversing links. 

The reversing links were then removed from the fixture.  The holes for the saddle attachment screws were tapped and screws in the holes used to hold the links together.

The sides of the links were then rough cut to shape on the band saw.

This photo shows the reversing links reattached to the fixture.  The mill x-y movement and rotary table rotation were used to finish the sides of the reversing links.

This shows the nearly finished reversing links.


 The rounded edges next to the eccentric link pins and next to the upper saddle attachment screw were  finished later using the setup shown on the right.

 That is a 5C Collet holder which is attached to the center of the rotary table --- dowel pins from the holder into mating holes in the rotary table make it easy to remove and later reattach the collet holder.

A 1/2" diameter rod with a 1/4" -28 thread hole was put in the collet and the reversing link attached to the rod with a 1/4" screw as show in the photo on the right.  The rotary table was rotated to make the round sides next to the holes.  I could have used this setup earlier on the link hangers, etc, etc. .

Link Block-HM132 & Block Rear Plate-HM132:  (See Engine Design VI):

A couple 1/4"- 28 Holes were drilled and tapped  in the fixture along the center line of the reversing link slot (3.75" radius).  The fixture was used to locate mating holes in the bronze disks shown in the photo.  The bottom disk is the correct thickness for the link block and the top one the correct thickness for the block rear plate.

After the disks were reattached, holes were center drilled for the rear plate attachment screws.   

Next, the disks were rotated under the end mill making a cut such as to leave sides at a 3.5" radius as shown being cut here and later at 4" radius cut on the other side. 
This shows the finished sides at 3.5" and 4" radius.  The two ends were also finished.  At this point the upper disk (the pair of rear plates) was removed.  
The next step was to trim the sides that fit inside the revering link slot.  These sides are at a 3.56" and 3.94" radii.  The milling cutter was set off the bottom so as to leave a lip. 


The photo shows test fitting the reversing link  over the link block to make sure everything fits properly before the link block pair was removed and sawed in half.

The photo above shows the completed link components with the sleeve bearings installed.    The Link Block Pin-HM133 and the Reversing Link Saddle-HM137 pictured were fabricated to match the design drawings.  Note that a flat washer and Nyloc nut are used to hold the Reversing Link Saddle in the Link Hanger.  The nut hasn't worked loose yet after an hour or so operation; if it does work loose a castle nut with cotter pin might be required.  Each reversing link has a screw in the side to limit the maximum travel of the block in the slot.   Recall that the slot in the original design was 2.5" long.  The slot is 2" long in the latest design so that screw stop will not be necessary.     

Eccentric Rods-HM141: (See Engine Design VIII)  The rods are machined from 3/8" X 5/8" bar stock --- two rods per bar.   The first step was to mill out the area of the yoke. 


The next step was to rough saw off the excess material along the shafts.
Next, the mill was used to finish the sides of the shafts.   
The holes were center drilled using milling table indexing as shown on the right.   Pilot holes for the Eccentric Rod were drilled.  Recall one side is threaded, the specific dependent on which eccentric it is used with.
Next, the bars were sawed in half and the end was rounded on the belt sander.  The rollers and a # 4 screw shown in the photo was used to as a guide on the belt sander.  This worked slick.
Eccentric Straps, Inner-HM138, Outer Upper-H139, Outer Inner-HM140: (See  Engine Design VIII)

The photo at the right shows the finished eccentrics and the parts used to make the straps.   

The steel outer strap was machined over size and then a section cut out of the middle for the two bars that will become the tabs.    The cuts were made with a saw and the ends finished on the mill.  The bars were drilled and tapped for the #6 screws used to hold the two halves together.  The bars were attached to the circular segments with #4 SHCS and then silver soldered.     
The strap tabs were machined as a single piece and the ends tapered for a pair of tabs as shown in photo.   These two tabs were cut off the ends and the ends of the reaming piece tapered and cut in half for the other two straps.    Recall that the width of the tabs was reduced to make it easier to achieve the required rotation between the inner and out straps.  The tabs shown here are the wider earlier design.
This photo shows shows machining a slot in the slide for the tab.
The tab was held in place by a #4 screw as shown in the photo.   That is flux and a couple pieces of silver solder rod in the cavity. 
This is the view after the flux and then the solder has flowed.
The inner strap was turned to the correct dimensions and then a slot cut for the tab.  The tab was soldered to the strap using the same technique as for the outer strap.
The outer strap fits nicely in the 3-jaw chuck for turning the correct inside diameter.  Next, the recess was turned in the middle of the strap using a boring bar as shown in the photo. 
The last step was to cut the slot in the outer strap for the tab on the inner strap as shown in the photo.   The inner and outer straps and the eccentric were assembled and rough edges removed as necessary until everything turned smoothly.   The inner strap was then cut in half.

Photo above shows the completed eccentric straps, rods and Eccentric Rod Pins-HM142.  The reverse  straps are on the left and the forward straps are on the right. 

The photo above shows the valve stem heads, rocker arms and rocker arm base in position.  It is at this point that the valve rods were trimmed to the proper length by positioning the valve piston in the middle of the valve cylinder and adjusting the position of the valve stem head such that it lined up with the rocker arm when the rocker arm was at a 45 degree angle.  At least a 1/4" excess length was left on the rod for subsequent adjustment.

The valve rod is a smaller diameter than the hole though the center of the valve piston which gives the valve stem head some slack to move perpendicular to the direction of the valve motion.   The position of the rocker arm base should be adjusted front-to-back as necessary so that the valve stem head lines up with the opening in the rocker arm without stress the valve rod.   The flanges on the sleeve bearings in one of the valve stem heads can be thinned or shimmed if necessary if the two valve stem heads are not directly across from each other. 

Next, the base was adjusted left-to-right and up-or-down such that that the link block pin holes in the rocker arm and valve stem head line up.  This may require trimming material off the bottom of the base to make it lower or shimming it to make it higher.  Once this was done, the base was clamped in place and the link block pins installed and each valve piston movement of  5/16" up and 5/16" down tested to verify that there was no side-to-side stress on the valve rod.  The position of the base should be adjusted further if necessary so that the valve rod is not under side-to-side stress over the entire valve movement.   Once this was verified, the mounting holes for the base were drilled into the crankcase (using the base as a template) and then tapped 6-32.   

Photo above shows the assembled valve linkages.  The next step was to adjust the valves.   A number of years  ago Artie Barkley at Cass told me to adjust the eccentric rods first and then the valves.    I did that and it worked great.   I took the upper valve heads off and used a depth gauge to determine the position of the valve.   I then adjusted the eccentric rods as necessary such that the upper most travel of each valve is the same in forward and reverse.  Next, the nuts on the valve rod lower end were adjusted so that the valve opening (as seen through the inspection ports) was the same when the main piston was top dead center and bottom dead center.  If everything is correct, the valve is open about 0.01" when the piston is at the top and at the bottom. 

This finishes the major parts of the engine.   Open items include the steam cocks and the bracket between the cylinders and the upper frame bar.   Those items and anything else that crops up will probably be covered in another web page to be done later. 

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