| Also known as | S648 |
| Diagram | Fig. 4 — INLET MANIFOLDS — Single Carburetter Models (T90, T100S, T100C) · ref 14 |
| Subsystem | engine top |
| Listed in parts books | 1968–1970 |
Spring washer
A spring washer used on inlet manifold fasteners, catalog number 21-0648 (also listed as S648).
This is a spring washer, part number 21-0648, also found in older parts books under S648. It shows up in the inlet manifold section of the catalog, on both the single-carburetter and twin-carburetter manifold setups.
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A spring washer like this one goes under a nut or bolt head to keep tension on the joint and resist it working loose from engine vibration. On the inlet manifold, that means keeping the manifold nuts snugged down so the joint stays sealed against air leaks.
It's a small, easy part to overlook when you're reassembling manifolds, but leaving one out or reusing a flattened one is how you end up chasing an air leak later. Keep a few spares on hand.
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