| Also known as | E6299 |
| Diagram | Fig. 2 — CRANKCASE · ref 21 |
| Subsystem | electrical |
| Listed in parts books | 1966–1974, 1979–1980, 1983, 1985 |
| Also fits (as replacement) | 1973–1974 · for 57-3733 |
O-RING 5/16 X 7/16 - Replaces 70-3253, 19-4593, 99-1176 - (Norton Oil Gage Fitting)
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This is a small O-ring, 5/16 x 7/16, that shows up all over the catalog wherever a threaded plug or fitting needs a seal instead of a fibre washer. Our records show it doing duty on the crankcase, the cylinder block and head, the chaincase, and the speedo/tacho drive fittings, and it's also called out as the seal for a Norton oil gauge fitting. That last note is the one to pay attention to - the same size O-ring gets used across different jobs and different marques, so what you're sealing on your bike is what matters, not just the number.
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It carries forward from the older 57-3733 part number, and the catalog lists 70-3253, 19-4593, and 99-1176 as prior numbers that this same O-ring replaces, so if your parts book or an old invoice shows any of those, you're looking at the same physical part. Given how many places in the engine and instrument drive this size O-ring fits, it's worth double-checking exactly which plug or fitting on your bike takes this seal before you order.
At this size and price point it's the kind of thing worth keeping a few of in a drawer - O-rings harden and take a permanent set over the years, and a tired one under a drain plug or gauge fitting is a common source of a slow ooze that's hard to pin down otherwise.
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