| Also known as | E3977 |
| Diagram | Fig. 1 — CRANKSHAFT AND CONNECTING RODS · ref 26 |
| Subsystem | engine bottom |
| Listed in parts books | 1960–1962, 1964–1965, 1967–1968, 1970–1971 |
ROTOR NUT 7/16X26
Rotor nut, 7/16x26 thread, secures the alternator rotor on the crankshaft — PN 70-3977 (also E3977).
This is the rotor nut, part number 70-3977, sometimes still found under its older E3977 alias in earlier parts books. It shows up in the CRANKSHAFT AND CONNECTING RODS section of the catalog, where it does the job of holding the alternator rotor secured onto the crankshaft end.
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The thread is 7/16 x 26, which is the standard size Triumph used on this fitting for the years this part appears across the catalog, 1960 through 1971. It is a small piece but an important one — the rotor has to stay put and stay concentric in the stator for the charging system to work right.
If you are replacing this nut, check the thread condition on the crank end and the rotor bore before you tighten anything back down. It is cheap insurance to have a spare on hand, but more importantly, get the fit right the first time since this is not a part you want backing off on you.
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