After several days of marathon CAD sessions, I’m about ready to wrap up this design. I have the mixer and exhaust to design/draw as yet but I thought it was time to post progress.
I re-worked the final assembly, using subassemblies which made the management of the project a lot easier so I’ll go through each of the components and then do a final main assembly. (it will be a miracle
if anyone actually reads this from beginning to end but… here we go).
The frame assembly with the crankshaft and main bearings installed. This is pretty much a repeat of what I posted up thread.
Following is the connecting rod. The original isn’t a fancy piece so I couldn’t see embellishing the model any. I’m using split bearings; I don’t know if the full size original uses them or not.
This is the exhaust assembly. It bolts to the underside of the head as you’ll see later. The lever coming out the side is used to “lock out” the igniter when the exhaust valve is held open. The grey slug on the bottom with the wedge cut in is part of the governor exhaust valve lock-out mechanism.
Here I’m showing a slightly different view. I also have the exhaust valve lifted against the spring.
This is a view of the intake Assembly. It’s atmospheric controlled as you would expect. This assembly bolts to the head immediately above the exhaust assembly.
This is the pushrod assembly. It has a roller that is captured and runs in a slot in the cam. The rear pushrod controls the star wheel mechanism which in turn controls the exhaust valve motion. The front pushrod and clevis is used to actuate the igniter.
On to the ratchet and star wheel which are at the heart of this engine mechanism. The green bracket is mounted to the engine frame and the ratchet, star wheel, and vertical post slide up and down within the bracket. This motion causes the star wheel to rotate and the alternate high spots / low spots on the star wheel allow four cycle operation.
In this view the mechanism is at the bottom of its travel and the pawl has just finished rotating the star wheel.
In this view the mechanism is at the top of its travel. We’re assuming that momentum has lifted the green weight, pivoting the long “teeter” bar so that it will engage the grey slug on the bottom of the exhaust valve (shown in the exhaust renderings above), thus allowing the engine to coast through one or more firing cycles.
Next I show the igniter. This is the back side, internal to the combustion chamber. The contact points will be made from tungsten; a material I’ve had good success with in igniter points in previous models.
Here is the igniter, front side (missing the springs). The “anvil” is the half-moon piece which is connected to the movable contacts. The hammer is the straight bar. When in trip, the hammer is drawn down off the stop. A lite spring bringing the anvil along with it until the contacts close. With additional motion a stiffer spring is wound as the hammer drawn away from the anvil. When the igniter trips, the hammer is drawn against the anvil by the heavy spring and then the lighter spring and momentum carries the hammer (and anvil) up against the stop as the contacts abruptly open.
This is the igniter trip assembly. The trip can pivot on a mandrel installed through the hole on the upper left of the main part (mandrel not shown). A spring and stop screw (also not shown) allows the trip to pivot on the mandrel but return to the position as shown. This is useful when the trip mechanism resets after it has tripped the igniter.
The offset cam and lever is actuated by the exhaust lockout to pivot this igniter trip mechanism away from the hammer on the igniter so that it will not trip when the exhaust valve is locked out.
Finally I give you (for those still with me) the assembled renderings. This view is near complete; missing only the mixer, exhaust, and water coolant piping.
A little more detailed view of the mechanism. Here, the push rods have been moved to the full downward position. The pawl has just completed rotating the star wheel. In this rendering, the engine is about to take a power stroke, the exhaust is not in lockout.
Here the pushrods are at their highest position. The exhaust valve has been opened by the star wheel. I can’t seem to get my CAD software to cooperate, but the green lever on the igniter trip mechanism “should” have lifted, rotated the eccentric, and moving the igniter trip over to the left a slight amount so that it clears the hammer on the igniter so the igniter doesn’t trip.
I’m hoping to complete this design in a few more days. Then I’ll probably put it on the shelf with plans to build the model at some future time; maybe this summer.