Have a Salsa Casseroll that I have set up as a 1 X 9 for commuting.

Front: 45t
Rear: 11-32 LX 9 speed
Rear Der: LX 9 speed
Chain: Ultergra / LX 9 speed

Set it up with a chain right out of the box (minus a few links). Ran it for almost 300 miles with no problems - even tried a 42t Biopace for a few rides.

Then I cleaned the chain to remove all that packing grease and lubed it with Tri-Flow. I've gotten thousands of miles out of my chains like this.

Well, ever since I've been throwing the chain off the chainring. When it happens, it happens when I'm around the middle of the cassette shifting to a smaller cog. It throws the chain off the chainring to the outside.

Everything seems to be adjusted and lubed just fine. It would be possible to remove one more link, but not 2. Is that the problem or something else? Could the packing lube left on the cassette be doing it?

Thanks.

bent chainring?
is the chainring centred to the middle of the cassette?

the chain length should be big-big + 2~3 links
if you cut the chain too short, it'll grind in the lowest gear.
too long can cause the chain to be thrown off occasionally.

why not install a bash guard?

Cleaning and relubing the chain can't be the culprit all on it's own so something else happened when you did it. Try turning the crank backwards slowly and watch the chain as it comes off the lower rear derailleur pulley to see if there is a tight link or a twisted or damaged side plate.

BTW, did you remove the chain to clean it and, if so, did you use the required special reinstallation pin? Did you install the pin properly?

Chainring is a new Salsa, not ramped or pinned. Pretty darned centered to the middle of the cassette. Straight teeth.

HillRider, I'd say the same thing. But, that chain rolls like butter on the derailler. I removed the chain to clean it. I'm using a connex master link just like on all of my 9 and 10 speed bikes over the last several years.

My thoughts are that the thick packing grease made the chain realively stiff and that the "less stiff" chain made the difference. But that can't be THE problem, just a symptom.

...and the link is on correctly.

Here's a couple pictures of the der at 45 x 11 and 45 x 32

couldn't possibly be a worn chain at 300miles... a mystery.
I would just install a bash guard and chain keeper or FD and call it a day.

Maybe the chain is on backwards. Ok, I know that sounds insane (and it might well be) but bear me out for a second. Given that depending on your riding style, you are unlikely to spend your time evenly distributed across the entire cassette, the chain will certainly spend more time at one particular angle. Now, given the nature of the chain, this angle may cause asymmetrical wear. Given that asymmetrical wear, installing a chain backwards might give you just the wrong amount of flex, and make you throw a chain.

I might be insane, but there is an easy solution, which is the only reason I post, just reinstall the chain with the plates that are currently facing inside flipped to face outside. It'll only take a few minutes, and who knows, it might work.

You need to add bash guards.

looks way better than the dork wheel anyways I like it!

Looking at your picture in the big cog, I would say that you should shorten the chain if you're happy with your gearing as it is.

On the chainkeeper ideas: The BBG bashguards are pretty awesome. They look good and are cheap. I run a single BBG on the outside and a 3rd-eye on the inside.

It appears from their website that they only go up to 44t. I'm running a 45t.