| Listed in parts books | Not catalogued by year yet |
ENG SPROCKET A10 21T 428
21-tooth, 428-pitch crankshaft engine sprocket for the BSA A10.
This is a 21-tooth engine sprocket for the BSA A10, sized for 428-pitch chain. It's a crank-mounted sprocket, not a Triumph part despite the PN prefix you'd expect on a Triumph shelf — the catalog description plainly calls it out for the A10, so that's what it is.
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The engine sprocket sits on the crankshaft and drives the primary chain back to the clutch. Tooth count and chain pitch both matter here for keeping your gearing and chain line correct, so if you're ordering this to replace a worn one, double check the tooth count and pitch against what's currently on your bike before you commit.
We don't have much more history on this one in our records, but the specs in the description are enough to confirm what you're getting: a 21T, 428-pitch crank sprocket for the A10.
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