| Diagram | Fig. 15 — CHAINCASE AND CHAINS · ref 6 |
| Subsystem | primary |
| Listed in parts books | 1974, 1976–1980, 1983, 1985 |
Chain tensioner blade
Primary chain tensioner blade for the chaincase, part number 70-5085.
This is the primary chain tensioner blade, part number 70-5085, living inside the chaincase where it rides against the primary chain and takes up slack as the chain wears. It's a wear item by design — the blade absorbs the friction so the chain and the chaincase itself don't. The catalog shows this part across a long run of years, so it's a common item to replace during a primary side inspection or chaincase rebuild.
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Grounded in the CHAINCASE AND CHAINS figure, this blade pairs with the primary chain and the rest of the tensioner hardware inside the case. If you're pulling the chaincase cover for any reason, it's worth a look — a worn blade lets the chain slap around and speeds up wear on everything else in there.
Catalog listings tie this part to the T140 Bonneville and TR7 Tiger 750 twins. If your bike isn't one of those, check the number against your own parts book before ordering.
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