My older mountain bike's (L.L. Bean Acadia Cruiser, says designed by Schwinn on the seatstays) outer chainring is worn (the teeth on it look like shark fins) and making my chain slip. I'd prefer to only replace the outer chainring instead of getting a whole new crank. But I'm having trouble identifying it to find a new part. All the markings have worn off. Any help is appreciated. I attached a picture.

Is there a part number on the back side of the crank arm, usually near the pedal eye? You have a Shimano crankset. They are well known for changing dimensional specs every few market cycles. But they do a good job at marking crank arms to allow you to search for specific stuff (only to find out sometimes that no one supports that version any longer...) Andy

The odds of finding the exact replacement are low. The middle and outer rings should be from matching sets to align the shift features. I would find the bcd of the cranks and replace the outer and middle rings from a matching set of rings. Sometimes with Shimano cranks rings of the same bcd are shaped differently and may require a rotory tool or a file to make fit.

This all may be fast approaching the cost of an inexpensive replacement crank.

Thinking that a replacement crank would be the best option, this LX crank (it's a M569) is from the time Shimano was playing with non-standard BCD's and patterns which only lasted for a single generation crank.

Agreed, you can get a replacement crank for $40, e.g., which sounds like a lot less hassle than trying to source such a non-standard part:

https://www.amazon.com/Shimano-Hybri...set&th=1&psc=1

I may be wrong, but from the photo it looks to me like the rings are riveted on; if true they are not designed to be replaced.


If you replace the crank it is possible that you would also need to replace the bottom bracket, unless your new one happens to match the BB.

thanks for all the replies, the part number was near the pedal eye, it is an M569. The outer ring is riveted on the spider. I found replacement outer ring/spider combos but they are more expensive than getting a new crank. so it looks like a new crank would be my best bet, thanks again.

That is essentially a 4 bolt 104mm BCD crank, however the large chainring is the spider/mount for the middle ring.

The only thing weird about it is the large chainring. You can find them fairly easily, sometimes the prices are a little high as it's somewhat unique and short lived.

The Shimano LX and XT from that generation are interchangeable, so you could use either large ring if you found one. Also the large ring/spider can be replaced with an optional 5 bolt 94 BCD spider to take standard compact drive rings.

I might actually have an extra one of those large/outer rings around here somewhere.

There is a whole crank on ebay here.

You are right: the big wheel is riveted.