Mechanics Corner: How to know your chainrings and crank is shot

I know many of us here put lots of miles on our bikes, which will result in wear of items. So the question may come up of when to put new chainrings, crankset, cassette, chain, pulleys on your bike.

Today, I’ll show you before and after worn chainrings and crankset.

Symptoms of crankset needing service: With chain off, front crankset doesn’t spin freely or makes grinding sound. This is a sign that bearings are worn, dirty or lacking grease. When crankset is off, spindle shows wear. This wear is due to crank grinding against the bearings.

Clean- brand new crankset:

Worn spindle due to seized bearings

Other symptoms: we had just put new chain and cassette on bike and chain would fall off front chainrings while applying force to crank. As you can see here, teeth are badly worn on force part of stroke. Inner chainring isn’t too bad- obviously the rider is a “masher”, not “spinner”
New vs old chainrings

New vs old cranks


By looking at above pics, you can see more wear on downstroke of right leg than left leg. ( my shameless plug to practice one legged pedaling drills - right @Coach_Theia ?).

I don’t have pics, but the outside of the crank arm was also worn from shoe rubbing crank arm.

I rebuilt this bike at the bike shop as special tools are needed to remove and press the new bearings into the bottom bracket.

This is my husbands trek checkpoint gravel bike with 2x11 Shimano Ultegra components.

Total cost: $320. Parts only
Crankset $199 from Jenson USA (shimano ultegra 50/34 175mm cranks)
Bearings from bike shop about $30 each= $60
Had also just changed out cassette. (Shimano 105 11-34) $47 from bike tires direct
And a Shimano ultegra/xt chain 11sp $33 from bike tires direct.

Since it’s a totally new drivetrain, we started waxing chains. That will be a different post.

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Thanks for posting this @Petals ! How can you tell the wear from right vs left? Proclaiming my ignorance here.

Wow the teeth are indeed worn out! I am not a masher or a spinner, but I never use the inner chainring- probably because I live on flatland.

What surprised me was the rubbing of the shoe against the crank arm… isn’t this something a rider would notice + be annoyed by right away?

I recently had the cassette and chain replaced on my outdoor road bike and oh-my-goodness, the difference!!

To see the other side of the chainring

Chain rings don’t have the same wear all the way around the chain ring. We know that most force applied from 12 o clock to 4 o clock position.

Everyone should own a chain checker. If the chain checker fall through the links of the chain, it’s time to get a chain or chain and cassette. (Determined by measurement of 0.5 or 0.75 for 11 or 12 speed cassettes.

Time for new chain and cassette on my mountain bike.

See how the chain checker here doesn’t fall between the links by the chainrings? This chain is okay.

A chain and cassette make a huge difference. Needing new ones because of wear means you’re riding your bike. Good job @Coach_Theia !

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I have a chain checker now because the last bike mechanic told me I’d need a new chain every 500 miles and I thought that was not the case. And confirmed it here in the forum. I actually check every week now.

The previous year I skipped a maintenance and I wound up needing to change the drivetrain and chain from so much wear.

I found a new LBS and I think they are going to be good. I had a talk with the guys about the other neighborhood shops and we seemed to be on the same page.

Thanks for the post it was a good lesson to learn.

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oh this is awesome @Petals i need to go back through this and get a chain checker - the trainer bike gets more wear than the IRL road bike and i need to be more diligent about checking it!

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I’ve had the problem of my heal rubbing the crank arm. I never really noticed it except on occasion when I could feel my heal tap the crank. I adjusted my cleats and it went away but as you can see from the wear on the crank that I was a little slow at getting around to making the adjustment.

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