Replace Pre-Unit Royal Enfield Primary Chain


Keith Fellenstein's 2002 Royal Enfield Bullet

Always turning and pulling a load, the primary chain is yet another oft-ignored motorcycle maintenance item. Fortunately, they’re usually quite robust, and outside of regular tension adjustment they typically require little attention.

Hidden from view as they are, it’s not surprising that many owners ignore them, yet they do need occasional replacement. True to its early-Fifties British roots, like many British motorcycles Royal Enfield’s familiar single-cylinder Bullet employs a separate engine and transmission with a chain-driven primary drive — as do even the newer “unit” engined Enfields; they may have fuel injection, but they still employ some old school technology.

BikeMasterThe primary chain plays an important role in your powertrain, transferring engine output from the crankshaft to the clutch, which then feeds the power to the transmission and finally the rear wheel. The basic design has stayed the same for decades, mostly because there’s really not much to change. Different self-adjusting schemes have been tried to help limit user maintenance, but the vast majority of chain-driven primaries rely on a simple manual chain tension adjuster.

That’s fine, but most adjusters are located inside the primary cover, so primary chain adjustment requires removing and refitting the primary cover. It’s not actually much of a chore, but it’s enough to keep some owners from ever checking for primary chain stretch. That’s a problem, because as the chain stretches it starts whipping up and down, aggravating wear to the chain and sprockets and presenting the real possibility of the chain hitting the inside of the primary case and damaging it.

For this How-To, we replaced the primary chain on Q & A man Keith Fellenstein’s 500cc 2002 Royal Enfield Bullet. As you’d expect from him, Keith’s given his old Enfield model care, including adjusting the chain regularly, so he was a little surprised when he found the primary chain stretched to its limit after 17,000 miles. Normally, we’d expect at least 20,000 miles, and we know Norton and Triumph owners who have done double that.

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