The same old chain has been on the singlespeed for a long time now - so long in fact that I couldn’t recall when it was actually installed. That’s not a good sign, but one you can get away with in a simple, robust system such as a single geared mountain bike.
After the Quickbeam got a new chain a few weeks back, the Bridgestone got to pouting a bit. So, when it looked like we were going to head for new trails this past Sunday, I tried to make it happy by cleaning it off and checking things over. Since the parts bins included several extra chains, I figured “heck, why not?” and popped the old one off and replaced it with a shiny new, not stretched SRAM 8 speed chain.
The new chain put a little push back against the tensioner again and set up right proper.
One slight problem…
In the above photo, I have moved the pedal about a sixteenth of a turn and created a dynamic new fashion in chainline behavior. In case it is not yet clear what’s going on, let’s look a touch closer…
The chainring, which has been happily eroding while the old chain was happily stretching, now finds that it can get quite a good bite on the new chain. As the reverse shark fin shaped teeth bring the chain around, they now have little ability or impetus to let go of said chain. This was occurring, mind you, with not a whole lot of pressure on the pedals. Pedaling a full revolution by hand was downright ugly.
Five quick spins of the hex wrench and bingo - here’s the culprit…
Those teeth should be nice and symmetrical. Which means it’s now time to play “What Local Bike Shop Will Have a Rampless 110BCD 36T Chainring In Stock?” (And, we are playing the Saturday afternoon with an early ride scheduled Sunday version of our game…). Much to my happy suprise, the answer was the first big store nearby. Though, I will admit, the wrench looked at the ring a little quizzically I handed him. But, I left with a brand spankin’ new RaceFace chainring and headed back to the workstand.
The above shot is now the two chainrings stacked on top of one another (new one behind). If you look at the larger version of this shot (you knew you could click on all those, right?), you’ll see the material that isn’t there on the old one showing through from the lighter colored new one. The camera was lined up over the one with the mark on it, just to the left of the “36″. The angle probably emphasizes the difference a bit more than it actually was on the ones which are offset. But, it’s taken a decent enough bite out of it to make ‘em all grabby.
So - greased it up and slapped it in place, and once again, the drivetrain was smooth and happy. (But, of course, while on the ride Sunday, some little skip was still in the system, when things were under extreme torque. Guess that means I’ll be getting ahold of another 16T Shimano BMX sprocket this week and might have more pictures to share…)