Install an LED headlight in an old Royal Enfield Bullet

LED headlamp conversion provides bright light for this 1999 Royal Enfield Bullet.

Seeking a better headlight for one of his 1999 Royal Enfield Bullets, Californian Mitch Smith installed an LED lamp.

"The LED should hopefully make 10,000-20,000 hours of run-time and be 'totally' immune to vibration. We'll see! These sorts of electrical things usually run either 30 feet or 30 seconds or 30 years.

"All I want it for really is as a fool-proof daytime running light — night riding holds no attraction for me anymore," he wrote.

Like my 1999 Royal Enfield, his Bullet has the U.S.-spec aimable headlight with its special hardware. Since they're only used in the U.S., it can be hard to find information about how to modify these.

Mitch graciously shares his step-by-step procedure and photos below:

There are many 5 3/4-inch LED lights available. Prices are from $20 (U.S.) to $100. Mine ran $40 and was intended for use in a Harley-Davidson Sportster. (If you ever thought your iron-barrel Bullet vibrates a lot, cage a 10-minute ride on a Sporty; that's about all you'll want. The Bullet is a Honda Gold Wing by comparison.)

Our headlights have an adjustment and retaining ring (A&R). This assembly has horizontal and vertical adjusters, three very thick plain "fingers," and a retaining spring lug.

Original U.S. arrangement includes inner bowl, adjusting screws and spring to aim the headlight.
The rear of the inner bowl must be cut off to make a bigger hole for the LED to fit through.
You'll also be cutting off the three long "fingers" that hold the inner bowl in place.
But do not remove the lugs that hold the spring and the two adjustment screws. 

The OEM headlight is sandwiched between a smaller inner thin front chrome ring and a black-stamped shell/bowl. The plain A&R fingers touch the inner shell and provide a bearing surface to allow for headlight aiming. The LED unit is MUCH thicker than the OEM sealed beam, which necessitates some modification to fit. 

The amputated rear of the inner bowl. Discard this.

Cut off the rear of the black stamped-steel headlight mounting bowl with grinder, leaving about 15mm of thickness to keep ring stable. The hardest part of the whole project was cutting the bowl apart evenly — a thin cut-off wheel would have made life easier.

Now with a wider opening, the inner bowl accommodates the LED.

DO NOT cut off the A&R retaining spring lug with the 1/4-inch hole in it. You will need this to create the new "pivot."

Cut off all three of the A&R ring's thick iron plain supporting fingers with the grinder. It was time consuming but straightforward to grind off the straight fingers. The A&R ring is too thin to just "bend and fatigue" these off.

Remains of one of the plain "fingers" after cutting. Don't try to twist them off.

Insert LED light into black cut-down bowl, and secure by using the thin front chrome ring and three original screws. You may need a gasket/packing/glue, but mine was snug as is.

The two original aiming screws help locate the LED in the assembly.
Don't cut them off.

Get a 2-inch-long, 8/32nd-inch screw and nut. Assemble these through the retaining spring lug hole and bend the soft steel screw over as needed to meet the groove in the headlight ring assembly.

Add a screw through the lug holding the spring and secure it with a nut below.
Bend the screw to reach the ring. It won't have to turn, it's there to hold things in place.
Drill a new hole next to the screw head to attach the spring. 

Drill a 1/8-inch hole next to the screw secured in the lug. Use the original spring and attach it to the new hole, then stretch it and secure it to the headlight mounting ring. I was able to stretch the spring into place using a wire loop and pliers, pushing the spring over into its original headlight bowl retaining hole when aligned.

All three of my A&R headlight ring-to-casquette retaining screw threads and the outer cover ring retaining thread found in the bottom of the A&R ring were boogered up. I retapped all four to 4mm x 0.7mm and replaced the associated odd collection of as-found screws with new Phillips pan head items.

Anyhow, that's my project. We'll see how long it lasts. But hey, if these lamps hold up on a Sportster?