Finding high quality materials here in China is a problem so I’m always looking outside-the-box to find materials for my parts. For these tappets, I ended up killing three birds with one stone. By using some hardened dowel pins from McMaster-Carr, I ended up with quality steel, a ground surface finish to ride against the bronze tappet bushings, and a hard material to ride against the cam ring.
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Hodgson Part 025, Tappet Bushings
The plans call for regular brass for the tappet bushings, but I decided to use sintered bronze bushings (McMaster-Carr P/N 6391K116) as my starting point. These are 3/16″IDx5/16″ODx1/2″LG SAE841 oil-impregnated, sintered bronze bushings.
Hodgson Part 024/069 Cylinder Studs & Value Adjusters
I’ve combined the cylinder studs and the valve adjusters on one page because they are practically the same thing. I bought one box of #4-40×3/4″ 18-8 stainless set screws from McMaster-Carr (P/N 92311A113). For the cylinder studs, the socket end was cut off and rounded. For the valve adjusters, the cup end was cut off and rounded.
Hodgson Part 023, Housing
The crankcase started life as a 125mm diameter by 300mm piece of Aluminum 7075-T6. I bought a stick of this long enough to make the front cover, crankcase, rear seal plate, air guide, impeller, and a few fixtures. The diameter was needed to accommodate the crankcase so I did end up wasting a little material on the other parts. To make the crankcase, I sawed off a 4.75″ section so I could move everything closer to the chuck.
Hodgson Part 022, Rear Main Bearing
For the rear bearing, I chose C63000 nickel aluminum bronze (known as QAL9-4 bronze here in China). This material has high strength because of the added nickel (needed for the thin mounting flange) and good wear resistance. The downside is this material is very “grabby” and tends to warp if you get it hot. Therefore, I’m going to machine it in two phases with a stress relieving operation in-between.
Hodgson Part 021, Front Bearing
For the front bearing, I chose C63000 nickel aluminum bronze (known as QAL9-4 bronze here in China). This material has high strength because of the added nickel (needed for the thin mounting flange) and good wear resistance. The downside is this material is very “grabby” and tends to warp if you get it hot. Therefore, I’m going to machine it in two phases with a stress relieving operation in-between.
Hodgson Part 019, Cam Gear & Assembly
I turned a stub arbor with a 1/4″ thick aluminum washer to mount the brass gear for machining. You want a good tight fit on the ID of the gear.
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Hodgson Part 018, Cam Ring
The stock for the cam ring was a piece of heavy-wall 4142 tubing, 3.25″ x 2.0″ in the annealed condition. You can used pre-hardened material, but if you do, you’ll need to anneal it before re-hardening and tempering.
Hodgson Part 014/015, Gears and Assembly
Many of the gears used in this engine need to be re-bored to a larger shaft size. There are drawings in the plans for holding fixtures to do this, but I found it easier just to use standard collets. This should also do a better job of maintaining concentricity between the bore and the gear O.D.
Hodgson Part 013, Jackshaft
I’ve mentioned before that obtaining quality material is one of my biggest problems here in China. Well, a corollary to that is that when I do have material, it’s probably not in the easiest-to-use form. For the jackshaft, I used a drop from a piece of 416 stainless plate that had been hardened to Rc35.