1-1/2 HP Gade Scale-Model Engine, Part 2

By Staff
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Two views of the cylinder head and cylinder. The valves still need to be made and installed, and the rocker arm needs to be machined, but otherwise it’s done.
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Lester Bowman’s patterns for his 1/3-scale Samson are a work of art
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The “rivets” holding the two halves of the muffler together were made from old spring wire.
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This promises to be a stunning engine when Lester finishes it.
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The muffler pipe is made from an old chromed valve stem. With the chrome removed in a lathe and new threads cut, it looks perfect.

Hello again, everyone. The past month has kept me busy with various projects, and as a result I haven’t spent much time in the shop. But, I have made some major strides in getting the 1-1/2 HP Gade scale-model engine ready to show. This month, I am only going to cover a couple items and then push forward: The cylinder head is done!

The cylinder head was an easy project, with everything falling into place as it should. When I first chucked the head casting into the lathe, I was worried it might have a sand casting flaw, as it had a small hole near the center of the plug casting and to turn it you have to turn away from the jaws. I took the cylinder head down to the proper size and then went in and started to turn it to the proper thickness. This was easy and fun and went really smooth. I turned it down to about 0.750-inch first, and when the head was ready for the raised panel I stopped it at 0.873-inch diameter. The fin looks very good and the parting of the head from the jawed stub showed me that the “flaw” was a well-designed feature on this model and served the head well, as it parted off nice and clean.

I drilled the spark plug hole with a no. 21 bit and threaded it for a 10-40 spark plug. I then took my 1/4-inch reamer and faced a spot on the head to make a clean, flat surface for the spark plug to seat. The valves had dimples in the centers of them, and I first used a no. 1 center drill to be sure they were correct, then followed with a no. 41 bit. I drilled the four mounting bolt holes with a no. 43, then I set it onto the cylinder and drilled my mounting holes for it and tapped them to accept 4-40 set screws. I then drilled the mounting holes with a no. 33 drill. I flipped the head over and drilled my counter-sinks first, then centered and drilled for my exhaust and intake. The head is now painted and sitting on the cylinder, but I still need a gasket or an O-ring and will have to cut the valve seats and lap in the valves after I make them.

The governor plate is mounted on the flywheel, and everything went well here, although I had to file a small amount of material from between two spokes to get the weights to set properly in the governor collar. I built two collars, as I thought I missed something with the first one and made the second a little larger than the specification sheet call for.

There are three rods (3/32-inch in size; two for the governor weights and one for the rocker arm) that have to be drilled with six no. 60 holes (1/16-inch cotter key holes; two on each rod). I like using simple jigs to make my work easy and accurate, and here again I?was happy with the outcome. In this case, I took a 1/2-inch piece of square stock and drilled a no. 41 hole (a hair larger than 3/32-inch) in it. I then aligned and cross-drilled a no. 60 hole in it. I?set my rods into the no. 41 hole, and using my drill press I drilled the no. 60 holes for the cotter keys. I used welding sticks for my rod, as I have some old ones that the flux is falling off of.

I also broached the flywheel to fit onto the crank, and will do the other as the model is fitted together; I do this to keep the spokes parallel with each other (something I learned from my very first model). The governor spring bolts are 2-56, and I purchased two that I will J-B Weld a few of the last threads before painting them; $.09 each is a lot cheaper than purchasing a new die to do the job.

The muffler is done now, too. I cleaned both halves and drilled the center with a “J” drill bit and tapped a 5/16-32 hole. Next, I drilled three no. 55 holes into the dimpled area again and aligned the two pieces together to finish. I was worried about what to use to fasten the two halves together, but after looking through my spring box I found an old spring of the right diameter. I cut a short piece off, heated it red hot, and let it cool. I then heated it again and let it cool once more, cut some short pieces off and used my flat punch to fit them into the holes. These are not rivets, but they look good enough that most people will be unable to see them, as they are very small.

For my muffler pipe, I once again went to my parts bin and got an old metal Schrader valve stem. I pulled the core and drilled out the center, and used my lathe to remove the nickel plating on the outside of the stem. I used my newly purchased die to thread it, and this part of the model is now finished as well.

I found a source for some brass acorn nuts that are 4-40, which I might use on the bearing caps and maybe the head, but more on this next month. Is this hobby great, or what?

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