So I was mtn biking, and when i would go up a steep ass bit of ground, the chain would make a popping sound and pop off the smallest chainring. Did it a couple of times at the same spot. I recently got a new chain. I dont know if that has anything to do with it.

Check for a bent tooth on the inner ring. A botched shift on low gear can often bend teeth and cause shifting problems or chain suck problems. It's probably not related to the new chain.

Just checked the gear and all the teeth look fine except two of them that are opposite each other have no tops. Don't know if that is normal or not.

New chain? Old Cogs? Skipping under load? = Worn out cogs.

Let's do a sanity check for a stiff link as well.

I got the chain replaced before it got to stretched out. Bike shop said it was within limits to not need new cogs. And it doesn't skip under load except on super steep stuff in the smallest chainring.

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I mean it doesnt skip under load but it pops off the smallest chainring on super steep stuff.

On outer and middle rings, there are often teeth that look flattened. This is normal and aids in shifting. On the inner ring, the teeth are usually the same size all the way around.

Cogs (aka cassette gears) can skip with a new chain and old cogs. Chainwheels (aka crank gears) usually don't skip with a new chain.

Ok. The cogs are fine. It just jumps of the smallest chainwheel on steep stuff. Do I need to check for stiff links in the chain? And how?

Back pedal the bike...slowly...while watching the rear derailer. If you have a stiff link, the derailer will jump slightly as the link passes over the jockey pulleys or you may be able to see the link as it passes the jockey pulleys. It will stand up and away from the pulley.

While you are doing this check, watch the chain as it passes over the small ring in front. The ring should be very straight. If you see a wobble, that is likely your culprit. You may also have the low limit on the derailer set too far inboard so that the derailer can nudge it off the ring as the frame flexes during hard efforts.

If all else fails, you can add a chain watcher to your bike. They look like this



Not real elegant but it does work.