| Also known as | 110-046-70, D301 |
| Diagram | Fig. 14 — CHAINCASE AND ALTERNATOR · ref 26 |
| Subsystem | primary |
| Listed in parts books | 1960–1962 |
PRI CHAIN 1954-62 PU TRI (Swing Arm) 428 70L
Primary chain for pre-unit Triumph twins with swing arm frames, 428 pitch, 70 links, listed for 1954-62.
This is the primary chain for pre-unit Triumph twins from the swing arm era, running between the engine and clutch on the primary side. The catalog lists it as a 428-pitch chain with 70 links, and the fitment window on file runs 1954 to 1962, covering the pre-unit swing arm frames of that period.
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The primary chain takes the drive off the crankshaft and runs it back to the clutch basket, so it lives inside the primary chaincase along with the oil bath that keeps it lubricated. Chains stretch with wear over the years, and a stretched or worn primary chain will rattle inside the case and can throw the alignment off between the engine and clutch sprockets.
If your bike's parts book lists this chain under the older part number, 110-046-70, that's the same physical piece under its earlier catalog identity. Worth confirming link count and pitch against what's currently on your bike before you order, since chaincase clearances can be tight on the pre-unit frames.
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