Thread: possible rear sprocket change?

I was going to put a new 42-tooth sprocket in my hk1 and i was wondering if you have to get a whole new chain to do that? Any help would be appreciated.

-zack

Hi Zack

as a general rule, I always change both sprockets and the chain and keep them together

this might seem excessive, but I swear I have seen a new sprocket eat the old chain up in no time

it seems they break in together and last a lot longer that way

just my experience

a chain and both sprockets are not that much $, but its your call

limited miles / year it should be fine either way

Originally Posted by a_smerek

as a general rule, I always change both sprockets and the chain and keep them together
this might seem excessive, but I swear I have seen a new sprocket eat the old chain up in no time
it seems they break in together and last a lot longer that way

Generally speaking, that IS sound advice and certainly takes a lot less verbiage than what I'm about to attempt to cover.
A worn (a.k.a. "stretched") chain will quickly erode sprocket teeth and vice versa. Usually, though, we're talking about someone rescuing a well-used, poorly-maintained, bike and those come with dirty/rusty & worn chain /sprocket sets as standard equipment. If your sprockets have teeth that are angled & worn to sharp points, time to replace everything. Stay on top of chain maintenance and sprockets can outlast chains by a wide margin. Best case, chains will always wear faster than sprockets. The thinking man's approach comes down to timely replacement of chains & sprockets as they reach wear limits.

The sprocket shown in the 2 pix had 11829 miles of use when the photos were shot. It's seen 6 drive chains and the current chain has almost 7000 miles of use. The relevant question: how is this possible? The answer is a long, multi-parter. I'll try to keep it as short as possible. First off, I replace chains at the first signs of wear. Typically, by the time the 3rd adjustment index mark is reached, the chain is done. That's about .500" of apparent "stretch" or roughly .0063" of wear per link. Std duty chains reached that point in less than 1000 miles. There's another reliable method...try lifting the chain over the rearmost edge of the wheel sprocket. If it can be lifted by 1/8" or more on the teeth, it's time to replace. Tired of the constant adjustment/replacement cycle, I upgraded to a $40 HD chain and got 3000 miles from it. After noticing the constant "shake & bake" appearance from conventional lube and the extreme loosening from even short offroad exposure, I went old-school and switched to molten paraffin. Admittedly, the process is impractical for most, but it works. At this point, I'm money ahead and haven't had to adjust chain tension for over 700 miles.

Take a close look at the sprocket. The red arrow shows a witness mark left behind by chain contact. That's a key concept. A good quality chain is a precision assembly and that precision spreads out the load to the base of the sprocket teeth, plus the rollers take up nearly all of the friction. Note that the ends of the sprocket teeth a virtually untouched. It's when the pins & rollers wear that the chain rides up on the sprocket teeth. By that point, the rollers no longer roll properly and everything wears out quickly. Timely replacements, as outlined above, will maintain the precise fit needed for efficient operation and long service life. Keeping the chain & sprockets lubed & free of grit will maximize ultimate service life. Both will minimize the need for tension adjustments.