Well, I went out for a beautiful spring ride in the country over the Easter weekend. It was gorgeous! I even had to take off the neoprene cockpit cover to stay cool. Sorry Kevin! I guess I’ll have to change my wardrobe to match the weather soon.
Anyway, I was on the final stretch of my journey home, starting off at a stop light, and the chain suddenly seized up in the middle of the intersection. I had to put my neanderthal arms out and row to the far sidewalk. That must have looked, well, awkward! And no, I don’t have video of that.
I found that the chain was broken at the back wheel – torn apart actually, but I couldn’t get the rest of the chain to pull free at the front. Looking under the seat to investigate, I found this…
It’s called an idler sprocket. Not coming from a recumbent background, these are unfamiliar to me. Apparently they help direct the chain coming from the rear wheel cassette to the chainrings at the front with as little friction as possible. Well, there’s a little friction now. You can see that the chain is now sideways and wedged between the idler and the bottom of the chain trough.
There is a small machine screw on either end of the idler axle. They come in through the velomobile shell and hold the axle in place. I unscrewed those and the whole assembly pulled out – with a bit of coaxing.
Here are the idler assembly parts…
The idler axle has a flange on one end to keep it from pulling through the velomobile shell. That insignificant looking rectangular piece of metal welded to the axle actually performs many duties: it keeps the sprocket centered, it keeps the chain return tube and derailleur cable from rubbing on the idler, and also prevents the axle from spinning and unscrewing those little machine screws coming through the velomobile shell. That important looking tube at the top is just a spacer for the other side of the sprocket.
There is no flange on the other end of the axle because the idler and spacer must be slid on. This is also the reason that I had some trouble getting the axle assembly out – it had burrowed a bit into the velomobile shell on that side. Not so good.
Here’s what happened to the plastic toothed idler sprocket…
Lesson Learned – The idler sprocket is an essential part of the drive train. If it fails, you’d better hope there’s a pub nearby. I’m replacing mine with a strong precision idler from Terracycle. I’m also looking into a new axle assembly which keeps the axle from eating into the velomobile shell. It would also make it super-easy to take the idler out for inspection or replacement. While writing this, I’ve even started thinking of carrying a spare. I just haven’t decided – spare idler or spare Guinness… Hmmm…!