Thought it was the RD/Cassette causing chain skip, now thinking it's the Chainring
 

I have been getting chain slip and/or chain intermittently falling off the front chainring (both to the outside of the big ring as well as inside of the small ring) when out of the saddle or applying a good amount of power (usually on the left pedal, from what I recall). It's almost thrown me over the handlebars several times. However, the symptoms usually present themselves when getting going from a stop and placing most of my weight on the left pedal.

Initially thought it was slipping at the RD/cassette, and started by replacing the chain. Problem still persisted, so I replaced the cassette. Looking now at the big chainring (50T). It doesn't show the sharp sharktooth signs, but it does have about 15k miles on it (I ride in the small ring most of the time [yes, I'm a spinner]). The FD and RD are both tuned properly. I'm including pics of the chainring; would like to know your thoughts.


http://i1266.photobucket.com/albums/...psqgl7nymt.jpg


http://i1266.photobucket.com/albums/...ps7sflqumq.jpg


http://i1266.photobucket.com/albums/...pspu1gaqne.jpg

http://i1266.photobucket.com/albums/...psibnowntl.jpg

It is just plain worn out. Congratulations! I could never conceive of wearing out a chain ring myself :)

Dropping a chain says "double check your front mech limit screws", before spending more money. Even if you think they are fine, tighten them up just to see if it goes away.

Presuming your mechs are tuned properly with limit stops set correctly...sounds like you've done the part replacing deduction...so you're buying new chainrings, they too are friction wear items-and safe to say when the cassette is toast they probably are too.

Thanks, guys. I've double checked the limit screws, and actually started there when this first started happening.

It's just strange to me, as when comparing how my chainring looks, it doesn't look like the stereotypical "shark teeth" type wear that usually cited online. However, they do look lkke there isn't much metal left on the teeth themselves, which could explain the slippage.

There seem to be a few different types of wear patterns. The "sharks tooth" is with tall teeth that actually bend somewhat.

In your case, if you look at the groove, on the forward side, it has a nice crisp "U" shape. On the rearward side, the groove cuts out at about a 45° angle, indicting high wear.

I'm not convinced the wear is causing your problems though.

Is dropping the chain just during shifting? Or are you dropping the chain while riding along?

You can get a "chain catcher" for the inside which may help.

Do your chainrings wobble significantly when going around in a circle? How much? Any signs of sharp bends?

It is also difficult to assess the condition of your FD cage from your photos. It looks bent a little bit near the bottom. Perhaps a worn FD could cause your problems.

Thanks for the info re: wear patterns.

No, the droppage (both to the inside of the 34 as well as outside of the 50) happens not during shifting, but only under high power load.

My mechanic (when we were doing intial troubleshooting about the issue) said the FD looked fine, and double checked the limit screws and cable tension.

The 50 ring is slightly warped, which I think may have happened a long time ago when, unknown to me, 3 (!!) chainring bolts had backed out, and was only brought to my attention by a mechanic (we looked at it together, so I know he wasn't screwing around with me). I had just started riding a few months earlier, so it's very possible that I wasn't able to assess the resultant flex caused by the missing bolts at the time. Anyway, he replaced the bolts, secured them with loctite, and I've ridden these rings for about 15k miles (probably about 12-13k in their slightly warped condition).

To some extent you can straighten a bent ring.

That is odd dropping the chain while under load.

Does it also have to do with the chain path (smallest or largest cog in rear)?

A new chainring certainly would be worth considering.

The front derailleur looks too high. Should be 1-3mm from the teeth of the big ring. Try adjusting so it's closer to the big ring.

Agree
One thing that might be a cause of your problem is wear and play in your shifters and rear derailleur. When this occurs, if you get up out of the saddle and sprint aggressively, the cage of the rear derailleur can move side to side as you rock the bike. I had this happen to me with a Campagnolo shifter that needed new G springs. I rebuilt the shifter and the problem was cured, but not before I dropped the chain in a high speed sprint and almost crashed into a tree when I veered onto the gravel shoulder of the road