| Also known as | E4578 |
| Diagram | Fig. 11 — CHAINCASE AND CHAINS · ref 8 |
| Subsystem | primary |
| Listed in parts books | 1964–1965, 1967 |
Oil seal
Sprocket cover oil seal for the primary chaincase, keeps oil from leaking past the sprocket shaft behind the clutch.
This is the sprocket cover oil seal that lives behind the clutch in the primary chaincase, part number 70-4578, also listed as E4578 in the older letter-prefix numbering. It shows up in the CHAINCASE AND CHAINS section of the parts book, which puts it right where the engine sprocket and primary chain live inside the outer cover.
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An oil seal in this spot does the basic job any oil seal does: keeps the lubricant inside the chaincase where it belongs and keeps it from working its way out along the shaft. On a primary chaincase that's wet-sump oiled, a tired or hardened seal here is a common source of a slow drip showing up on the floor under the left side of the engine.
Our catalog record ties this one to appearances spanning 1964 through 1967 across four listings, so it's worth checking your own parts book or having us confirm which cover and shaft it mates to on your engine before you order.
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