i have a truvativ crankset, discontinued some time back. the outer chainring has had the most use and along with it wearing out, took out the chain and cassette. replaced the last 2 items and been looking for another cr. i thought i found an equal used replacement today. holes matched, #of teeth, the fit of the spider. lookin' gooooooooood. paid $3. got home, took the old one off and compared, just to be sure. awright! we on it now!

put the replacement on and went for a test ride around the block.

dude.

i like to cripped myself somewhat permanent barely a block away. started in the lowest of the low and worked up. soon as the chain got on the outer ring, the chain started hoppin, jumpin' ALLLLLL up 'n' down the back row. then it all seized up.

to shorten the story, got home, took it all apart again and started really comparing the 2
rings. couldn't find any difference for a bit. i aligned the hole on the replacement that goes behind the crank with the stud on the original and lo and behold.....

the teeth were a half tooth off in alignment location, and the bolt holes no longer lined up. i might have caught it at the shop if'n i had taken my tools along and switched there.

the replacement also had a bulge pointing inside the ring. thought maybe i had oriented it wrong, but after doing a re-alignment it made no difference. still all wrong. boo hoo.

so, boys and girls, check absolutely everything on the crs.

one other thing i noticed was that the crankset had little studs on the inside of the rings (except the lowest one), i guess for helping the chain move up. the replacement hadn't those.