| Also known as | E3851 |
| Diagram | Fig. 1 — CRANKSHAFT AND CONNECTING RODS · ref 18 |
| Subsystem | engine bottom |
| Listed in parts books | 1964–1970, 1974 |
ROTOR KEY-500 HALF MOON
Half-moon woodruff key that locates the alternator rotor on the crankshaft.
70-3851 is the half-moon key that locates the alternator rotor on the crankshaft. It's a small woodruff-style key that sits in a slot on the shaft and keeps the rotor indexed correctly so the ignition timing stays where it should relative to the crank.
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This one shows up in the crankshaft and connecting rods section of the parts books, so it's living right down in the bottom end where the rotor mounts on the end of the crank. The older reference for it is E3851, which you'll see in earlier parts books before the numbering changed over.
It's a cheap piece of hardware to have on hand. If you're pulling the rotor for any reason, it's worth checking this key for wear or damage rather than reusing a tired one, since a sloppy fit here can let the rotor shift on the shaft.
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