Motorcycle Classics

Replace Pre-Unit Royal Enfield Primary Chain

Reader Contribution by The Motorcycle Classics Staff

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.

The 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.

Our Enfield’s primary chain was so stretched it was about to start rubbing on the cover support pillar.

Fortunately, this is a pretty easy job and quite within reach of the average weekend warrior. Outside of a torque wrench and a block of wood (more on that later), it doesn’t require any special tools, and even if it’s your first time you can probably complete the job in a relaxed morning. That’s assuming, however, you don’t find any surprises once inside. Those surprises can include worn clutch plates (clearly visible when you remove them); worn engine and/or clutch sprockets (highly unlikely); and a worn chain tensioner shoe (ours was fine). If you find any of those issues, your best bet is to just stop, order up the necessary parts and finish the job after the parts arrive.

Back to that torque wrench and block of wood: The crankshaft and clutch hub nuts are only torqued to 40ft/lb; the alternator stator and clutch cover bolts are torqued to 7ft/lb. The block of wood is to lock the clutch drum, as you’ll see in the How-To. As always, we suggest having a good shop manual on hand for parts identification and placement, and to confirm proper torque specs.

1. Disconnect the battery as a general precaution. Remove the left footpeg, then remove the cotter pin securing the rear brake rod from the brake lever. Remove the brake light switch bracket followed by the brake rod and let the brake lever swing down out of the way.

2. There is no drain plug for the primary, so make sure to have a large drain pan. Remove the large nut in the middle of the primary cover and gently remove the primary cover, letting the oil drain. Clean out any excess oil.

3. Remove the three nuts and washers securing the alternator stator. Remove the stator and hang it from some wire, as shown. Remove the nut and lock washer securing the alternator rotor. We were able to break it free easily with a hammer blow to the socket wrench.

4. With a felt tip pen, mark the rotor face for orientation when reinstalling. Remove the alternator rotor. Locate the Woodruff key that keys the rotor to the crankshaft and remove it. Finally, remove the spacer that fits between the rotor and the primary drive gear.

5. Next, loosen the adjuster so there’s slack in the chain, then remove the lock nut and nut securing the adjuster to the primary case. Remove the adjuster.

6. Working in a cross pattern, remove the three bolts and washers securing the clutch pressure plate to the clutch hub. Note there are six springs total, three that fit on the outer securing plate and three on the pressure plate.

7. Remove the pressure plate followed by the clutch discs. The discs alternate between fiber and steel; keep them in order to ensure they’re reinstalled correctly. Next, remove the clutch pressure plate pushrod, as shown here.

8. The clutch hub nut is a locking-type nut and can require a little more effort to remove than the alternator rotor nut. It can be removed with a socket wrench by putting the transmission in first gear, then reinstalling the brake lever and locking the brake so the transmission won’t spin. Or, as we did, you can simply spin it off using an air wrench.

9. Remove the nut and spring washer. The clutch hub will often just wiggle loose, but ours was stuck tight. To remove it, we used a universal puller, using the three clutch cover bolts to secure it to the clutch hub then slowly tightening the center bolt against the transmission input shaft. Doing it this way made it come loose easily.

10. Finally, lift the front sprocket, clutch hub and chain away from the engine as an assembly. At this stage, check the teeth on the sprocket and hub carefully. Ours were fine.

11. Confirm the replacement chain is correct. Wrap the chain around the sprocket and clutch hub and reinstall the sprocket and hub to the engine in the same way you removed them. You may have to spin the transmission input shaft until the splines line up properly.

12. We didn’t reinstall the brake linkage to tighten the clutch hub nut. Instead, we cut a piece of hardwood to fit so it would lock the inner and outer hubs together as we tightened the hub nut against engine compression. Crude, yes, but a good trick and it works well.

13. After installing the lock washer and clutch hub lock nut and torquing to 40ft/lb, reinstall the clutch cover pushrod.

14. Reinstall the clutch plates in the same order as they were removed, followed by the pressure plate. Place three of the springs on the clutch cover locating studs and three on the cover securing plate. Using a cross pattern, bolt the securing plate down to 7ft/lb.

15. Install the rotor spacer and the Woodruff key. Install the alternator rotor, then the lock washer and nut and torque the nut to 40ft/lb. Install the alternator stator and tighten the securing nuts to 7ft/lb. Check the air gap between the rotor and stator. It should be 0.010-inch all around. If it’s not, loosen the nuts and adjust the stator as necessary.

16. Next, make sure you have proper chain tension. Our book said there should be 1/2-inch total deflection. Adjust by loosening the adjuster lock nut and screwing the adjuster up or down. It takes a minute to find the right spot. Finally, spin the engine over and check to make sure there are no tight spots.

17. Clean the mating surfaces and reinstall the outer primary cover. Remove the level screw on the side of the cover and fill until oil just starts to drain out. Keith uses ATF in his Enfield primary,  but not everyone agrees with that.

18. Finally, reinstall the rear brake rod to the brake lever, followed by the brake light bracket, washer and cotter pin. Next, reinstall the left footpeg. Finally, if you disconnected the battery, hook it back up. You should be ready to go.

  • Published on Dec 11, 2015
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