Replace Chainring?
 

On my last ride the chain came off of the middle chain ring twice. Does the ring look
https://cimg9.ibsrv.net/gimg/bikefor...682c02bc36.jpg
like it needs to be replaced? Please note, it is paraffin not dirt on the crank.

I wouldn't expect a worn ring to cause the chain to drop. There are other things more likely to be going on. One might be developing a bad habit of making a chain ring shift and not letting it complete before you start to coast or stop pedaling entirely.

I think if you wrap a new chain around that ring and can pull it snug in one direction, if you see a lot of daylight under the chain, then the ring is worn. But still not sure why that'd drop your chain without something else being amiss.

Yeah, like Iride said. Plus, that big ring looks more worn to me.
Mine never reach that point. I replace well ahead of time, at the same time as cassette and chain.

I don't use the big ring anymore. The bike is more than 30 years old. The middle chainring has been replaced once. I am considering the following. Go single chainring and change entire drive train. Another option would to purchase a new bike.

Sounds like a good approach. To my eyes, that inner ring looks like toast. I bet the chain is stretched a lot. If so, the cassette/freewheel is not likely to work with a new chain. So, chainrings, chain and cogs? Not much to save. Good time to consider whatever new system/number of cogs you want. Looks like you got good use out of these ones.

If I did that, I’d be bankrupt

Haha. I really just meant that, for me, the rings can make it to 30 to 40 thousand.
Cassette 15 grand. Chain 5k. So I try to find a common junction for the rings.

Them idle ring is clearly very worn in the peak power zones (6&12 when the crank is horizontal).

IMO this CAN cause the chain to fall off via the same mechanism that causes skipping on worn rear sprockets. Doubly so if you get more issues on less aligned gear combinations.

So definitely consider a new sprocket, since this one is toast or beauty so. However, I suspect that the chain is probably equally near the end of it's life. So check that too, so the old chain doesn't kill the new sprocket.

This is a mountain bike with cantilever brakes. The dropout space is 135mm. I may not be able to find non disc hubs. I see no reason why I cannot use them with rim brake rims. It is currently 8 speed. My plan is 10 speed with 1 X chainring. I will wait for the Winter to begin work.

So long as the rim is designed for rim brakes the hub doesn't really matter. However I know White Industries makes a 135MM rim brake hub called the MI5 in various versions to work with whatever you need.

That hub would be worth more than the bike.

Without knowing what bike it would be tough to tell but it is a hub that exists in the framing I had. Back in the day a higher end MTB could have been spec'd with WI parts.

My experience is that 90° from the crank is where the chain wear is typically worse. Often visible by elongated and gently sloping valleys on the pulling side of the ring.

In this case, the teeth on the middle ring almost exactly 180° opposite the crank look absolutely chewn up. Now, one can have some odd shaped teeth in that area for shifting, but it just doesn't look right to me.

I agree that there are times when worn rings can impact dropping the chain, especially when cross-chained.

Middle rings usually aren't that expensive, and I'd probably snag a new one.

I think that middle ring looks knackered around the crank arm.

I am looking for a 1 X crankset. According to my measurement, I need a 55mm chainline. At this point, I don't know how to achieve this.

standard 74/110 and 58/94 chainrings should be fairly easy to find / replace - unless they are unique / specific chainrings (examples include some vintage XTR and middle ramped XT rings etc)

but please note - some of the better replacement chainrings can be a bit pricey

on a couple of older bikes instead of replacing the individual chainrings I replaced the entire crankset after finding relatively inexpensive crankset … on one bike used a STX RC crank - on another used a Sugino crank - and on one bike went with a more recent external bearing design SLX crankset and BB … please note - vintage 170 mm cranksets can be more of a challenge to find than 175 mm cranksets if 170 is desired size

old hubs and wheelsets are also fairly easy to find

if the bike is a fairly good quality bike - probably worth the expense to replace the parts and continue to ride it

If you go with 1x, look for special drop stop rings of one sort or another.

Wolf Tooth was one brand.

https://www.wolftoothcomponents.com/...ons/chainrings

I think other brands use wide/narrow teeth.

The two big chainrings are 110mm. I have not calculated the small one.