Thanks, Charlie. It's been a fun challenge so far working on this very old engine!
And now, on to the
CRANKSHAFT
As mentioned previously, the crankshaft on this engine had a lot of wear and looseness. I was surprised because it seems to have wide and substantial bearings -- not like the stamped sheet metal bearings on some of the later engines:
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This was kind of deceiving, however, as I found out after disassembling. It turns out that only a small portion of the bearing stanchion was contacting the shaft. This is why the amount of wear was so much greater than expected. Here is a drawing of the original crankshaft configuration (upper view) and the proposed design (lower view) with sintered bronze bushings:
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It's perfectly understandable why they designed the bearings this way. It is much more tolerant of misalignment between the bearings due to routine manufacturing variables. This was a mass-produced item, and at the end of the day, the easier the engines went together, the more engines they could send out. The only downside was a higher susceptibility to wear over the years of use.
In repairing the worn bearings, I've decided to make a new crankshaft, and ream out the bearing stanchions for some Oilite sleeve bushings. In addition to providing considerably more bearing surface, the Oilite bushings are made of an oil-impregnated bronze material, which releases a small amount of lubricant when friction builds up. So, if someone neglects to oil the bearings, it's not such a big issue with the Oilite bearings.
Here's a picture of the original crankshaft. Note the grooved area on the right-hand end. This the crank end, which apparently took most of the radial thrust from the engine:
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The original shaft had a diameter of 4.5 millimeters (0.177"), and I will making the replacement shaft from 3/16 (0.1875") O-1 drill rod. Note that the shaft features a #4-64 threaded extension on one end. This is for attachment of the crank/eccentric assembly. It's kind of a tricky feature to reproduce, given the small diameter and length, so I will be using the threaded end from the original shaft. As shown in the drawing below, the original crank end will be cut from the shaft, the cylindrical end turned down to 0.125", and fitted to a hole in the end of the new shaft:
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The threaded end piece will be secured in the new shaft with Loctite 609. When properly cleaned and fitted, this provides a joint far stronger than press-fitting, and as good as pinned joint, without the need for pinning. The only way to disassemble the joint is with heat from a torch. Below is a picture of the original shaft, the "donated" shaft end, and the new shaft with a hole to accommodate the modified shaft end:
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The opposite end of the shaft is threaded #8-32 for the pulley. This thread could normally be cut with a die mounted in the lathe tailstock, but O-1 tool steel is not the most machinable of materials. I decided instead to single-point the thread on the lathe, taking light successive cuts, frequently checking the fit with the pulley:
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After threading the pulley end, I mounted the shaft in the mill to cut a small flat near the center of the shaft for the flywheel setscrew. Here's the finished shaft, along with what's left of the original shaft:
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Next installment will be reaming out the bearing stanchions, and installing the Oilite sleeve bushings.
(to be continued...)