This build will be a 1/5th size model of Joe Fidd’s 15 HP Witte IC engine manufactured in Kansas City, Missouri in 1911. You can see this engine in the Willock building at the Rough and Tumble Engineers’ Historical Association in Kinzer Pennsylvania. Joe told me this engine powered a water pump for a Rhode Island Estate during it's working career.
Below is a youtube video of it that someone took several years ago.
The engine is a typical “hit and miss” engine; the governor controlling the speed of the engine by denying the engine power strokes. The method of this control however I find somewhat bizarre. The engine has an atmospheric operated intake valve and an exhaust valve that operates off a cam on the side shaft. The exhaust valve is lifted during every exhaust cycle regardless of whether the engine fires of not.
Engine speed is controlled by allowing or denying fuel to be brought in with the air during the intake stroke and this is accomplished via the operation of a third valve, up-stream from the atmospheric controlled intake valve in the air intake. The operation of this third valve is controlled by the fly-weight governor, located on the side shaft.
The full size engine is water cooled, has a magneto driven by a friction wheel that rubs on the flywheel, and has a compression release to assist starting; none of these will be reproduced on the model. The full size does have a fuel pump which will be modeled.
Ever since George Britnell introduced me to cutting helical gears I’ve been making my own helical gears. George seems to knock these off with barely a thought and he produces beautiful gears. Mine aren’t nearly as pretty and I will attest that there is a lot of thought involved, but I seem to produce serviceable gears. I thought I’d get the fabrication of the helical gears behind me early in the design because the pitch diameters of the gears determine so many of the other measurements on the engine. There is no need to spend days with the design of a model, only to discover you can’t make or purchase the gears you plan on using; knowing that substituting different gears will result in changing so many measurements in the design of the model.
I decided to cut these gears from brass, thinking the fabrication of brass gears might be easier than steel. I also have a growing supply of gear cutters and with careful planning I was hoping to use some of the ones I had without having to purchase even more. To that end I settled on a diametral pitch of 18, with the gears having eight and sixteen teeth.
These were fairly large gears to cut with a whole depth of over 1/10th inch using Chuck Fellows handy-dandy helical gear cutting fixture. I made several passes around each gear, increasing the depth of cut at around .020 inches per pass. The process was slow but the result was serviceable gears; though a little filing was require to have them mesh cleanly. Though they are a bit noisy they should work well.
In the first picture I’m forming a gear blank.
Once the blank was formed it was time to cut the teeth. In the second picture I’ve just finished forming the eight gear teeth on the crankshaft gear.
With the gear teeth formed, the third picture shows me reaming the gear to the crankshaft diameter size after I had first drilled out the center and bored it to near size.
In the fourth picture I’m parting the completed gear off its arbor.
Forming the side-shaft cam gear followed pretty-much the same process. The fifth picture shows a photo I took while cutting the gear teeth.
With the gears complete I mounted them in a test fixture to make sure they meshed smoothly and the designed distance between the crankshaft and side-shaft were correct. With that verified I moved on to complete the design of the engine.
The final attachment is an image of the complete design from my Alibre design tool.