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Friday, April 21, 2017

How I made my left-shift Royal Enfield 4-speed shift right

The suspense is over. Finally, here is my report on my first test ride after extensive efforts to improve the shifting of my 1999 Royal Enfield Bullet:

It worked! Shifting is better than ever before. My four-speed Royal Enfield with left-side shift linkage now moves cleanly between gears and even downshifts without missing gears.

There's a good reason for my delay in writing, and it felt like this:

"CLUNK!"

Of course you couldn't really hear the clunk while riding, but that is what it felt like, a real disappointment after my initial efforts to improve things. If you've forgotten where this started, way back in December, here's a link to Part 1 of my campaign to improve shifting action.

Now, pulling over and inserting my head beneath the motorcycle I saw that the left-shift linkage I'd tried so hard to rebuild and improve was striking the frame of the motorcycle as it reached to activate second gear.

Not always: sometimes the linkage made it to second gear and, when it did, everything was wonderful. I could even downshift reliably.

That had been my goal. The linkage had been loose and wobbly and I had straightened and tightened it and removed places where it bumped into other bits of the motorcycle. It should now be near perfect and, yet, every so often:

"CLUNK!" And it got stuck with only first gear and neutral available.

With my head under the motorcycle I could see the the linkage wasn't just brushing the frame. It was ramming it.

Arrow points to linkage arm contact on motorcycle frame.
All I could think was that, in straightening and tightening the linkage, I had increased its reach as it moved, and eliminated the wobble that would have forgiven any impact. So now it sometimes hit the frame when it moved.

The obvious solution seemed to be to rotate the linkage slightly clockwise where it attaches to the shaft that carries shifting from the gearbox, on the right, to the left side of the motorcycle.

I tried. I couldn't do it. The upper arm of the linkage contacts something (the front sprocket?) that prevents it from being relocated. (Remember, the linkage is so hidden behind the primary drive cases that most adjustments must be done by feel or by removing the linkage entirely — I couldn't see what was blocking me.)

Let me tell you, ladies and gentlemen, as far as this linkage goes, there is very little extra room in the original design of the motorcycle — designed to shift on the right — for this added bit of mechanical mayhem to move shifting to the left.

Linkage arm hits the frame at this point (arrow).
So I resolved to just very gently remove some of the metal from the ends of the linkage arms at the point where they hit the frame. Too much, I thought, might weaken them since the impact must be happening very near the holes for the bushing that holds the damn thing together.

Linkage arm smoothed (at arrow) to eliminate contact point.
(I also filed down the flange of the brass bushing to prevent it contacting frame.)
In the end, I could safely file off just a little metal. But it worked.

Thank goodness. I am delighted.

Here's my prescription, with explanatory links, for fixing the left-shift linkage of four-speed Royal Enfield Bullets:

1. Tighten up the gearshift lever.
2. Replace nylon linkage bushings with metal bushings.
3. Tighten linkage attachment to the gearbox shaft.
4. Eliminate interference with the linkage movement.

2 comments:

  1. Rube Goldberg smiles at you from his perch in Paradise.

    ReplyDelete
    Replies
    1. Thank you! My only regret is that I found no way to somehow insert a yowling cat or leaking watering can into the mechanism.

      Delete

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