I began work on the partially-finished one third scale New Holland engine this past weekend, and in taking a closer look at some of the parts that had already been made, I discovered a couple of minor issues. One, what should be bronze bearings for the crankshaft were made out of aluminum, and the crankshaft itself has a taper on both ends of the shaft from .212" to .204," so a new crankshaft and proper bronze bushings will need to be made. (Minor problem!)
The next thing I noticed was an odd, grinding sound when rotating the crankshaft that seemed to be coming from the timing gears. This lead to discovering a major dilemma that I wasn't sure could be resolved. I noticed that the cam shaft was bent (for some reason, the picture showing the bent shaft is not where it belongs, but ended up at the bottom instead, and I don't know how to change its placement- just click on it.), causing the large cam gear to be at an angle, causing only the outside edge of the gear to make contact with the crankshaft gear. Also, as you would turn the crankshaft, the spacing between the gears would go from too-tight to too great a gap. At first, I thought that the easy solution was to put a new straight shaft in replacement of the bent one. At this point, the first picture shows the problem.
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It turns out that the real problem was that the cam shaft hole was drilled .035" lower than called for in the blueprint. This left the gears not even touching. So, the problem to solve is how to move a hole up 0.035". One solution would be to use a larger end mill, drilling the larger hole to the specs, then making a bushing and reinstalling the correct sized shaft.
Then I got a brilliant idea that I wasn't sure would actually work until I tried it. I made a new shaft, starting with half-inch steel rod. I turned one end of the shaft down to the proper size for the cam gear, then I offset the steel rod .035" and turned the other end of the shaft, leaving a small spacer in between the two ends. This now gave me a shaft that I could rotate, raising or lowering the large cam gear, until the valve lash was correct. I then put it together, and it seems to work perfectly.
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This engine is going to turn out to be quite the project. It almost seems as if two completely different people worked on this engine before I received it. The first person, a qualified machinist who worked on it by day and his five year old son, who worked on it by night! Much of the work is done far beyond my abilities, and yet other parts look like they were done with a file, a drill press, and a hammer! All of the called-for model engineer threads were done in other thread sizes, seemingly at random. I finally figured that where it called for 3/16"-40 threads, things were tapped 12-24, leaving it impossible to put the correct threads in, at this point.
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There are still a couple of other threads that I have not figured out, but they are certainly not the ones called for in the blueprints.
All in all, I am still not disappointed, as the price was one that reflected the amount of work that would be needed, and the challenge of figuring out how to correct problems is part of what I enjoy in this hobby! I always learn from these experiences things that will help me in a future build.
I hope this all makes sense, and that it might help someone else who ends up with a similar problem. I know I am always looking for tips when it comes to machine work, and have learned a lot from other posts from guys who are far more qualified machinists than myself.
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