| Also known as | 2T, E6309 |
| Diagram | Fig. 5 — CYLINDER BLOCK AND HEAD TR7RV · ref 1 |
| Subsystem | engine top |
| Listed in parts books | 1967–1968, 1970–1971, 1974, 1976–1980 |
Cylinder base washer
Cylinder base washer (base gasket) that seals the joint between the cylinder block and crankcase on Triumph unit twins.
70-6309 is the cylinder base washer, better known around the shop as the base gasket, that sits between the cylinder block and the crankcase mouth on Triumph's unit-construction twins. It seals that joint so oil and combustion pressure stay where they belong instead of seeping out at the base of the barrels.
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This one shows up across a long run of catalog pages for 650 and 750 twins, including TR6, TR6R, TR6C, and T140V cylinder block and head listings, so it's a part that stuck around through a lot of engine updates. If your parts book lists it under the older 2T or E6309 designation, that's the same physical piece under a different catalog number.
When you're pulling barrels for a rebore or a top-end refresh, this is one of those gaskets you replace as a matter of course rather than reuse. Keep the surfaces clean and flat before fitting a new one and you won't have oil weeping out at the base of the cylinders.
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