| Also known as | T1603 |
| Diagram | Fig. 14 — CHAINCASE AND ALTERNATOR · ref 2 |
| Subsystem | primary |
| Listed in parts books | 1960–1962 |
INNER CHAINCASE
The fixed inner cover of the primary chaincase, from the alternator-equipped primary drive setup.
The 57-1603 is the inner chaincase, the fixed cover that bolts to the crankcase and forms the engine-side wall of the primary chaincase. It sits behind the primary chain and alternator, sealing the inner chamber before the outer cover goes on over the top. In the parts book it turns up under the CHAINCASE AND ALTERNATOR figure, alongside the alternator itself, which tells you this is from the era when Triumph ran the alternator inside the primary drive rather than out on the timing side.
Read more
Older parts books list this same piece as T1603, so if you're working from an early book or an old invoice and see that number, it's the same physical part as 57-1603.
Our catalog record on this one is thin - it shows up in only a couple of listings and the year span is narrow, so treat it as a guide rather than gospel. If you're not certain your primary case matches this configuration, bring in your old cover or give us a call before you order.
We've never carried this one. Tell us what you're after and we'll go looking — you'll get a price and photos before you commit to anything.
Sorry if we got something wrong here. If you think this information isn't correct, .

