gnrboyd

Hello,

I have a Trek FX 7.4 Hybrid with a Shimano FC M-391 crankset (170 mm - 48t x 36t x 26t – square taper) . I have close to 12K miles on the bike and have noticed some wear on the cassette (9 speed) and middle chainring (which I use most of the time) but I am not sure if they are bad enough yet to replace. (see attached photos) Last season, I would occasionally have what appeared to be a chain skip but it seemed to be after a shift or when I increased power suddenly. Again, it was only occasional and made me think that at least part of it may be caused by rider error. (By the way, I replaced my chain at about 8K so I have around 4K on this one and it appears to be in good shape at least in terms of chain “stretch”.)

To give you a better idea of my riding (if that matters), I ride primarily a flat gravel trail (fine/hard packed) when the weather permits but will ride roads occasionally also. I ride at a pretty consistent pace and average around 15-15.5 MPH over a 30-50 mile ride.

From a little searching, it looks like the Shimano chainring part # is Y1LD98090 (middle ring) and could be a little challenging to find. I also have considered changing the entire crankset as it might be a more economical option.

Do you think there is enough wear to replace either of these components? If not, any idea how much life they have left? What would you suggest in terms of a replacement if I replace the whole thing? I have the chain guard on mine but have noticed many replacements don’t have it. I would prefer to keep it (not sure why) if possible.

Thanks for any comments or suggestions you may have.

CannonLA99

That's NOTHING, I should show you the sharkteeth on my 20 year old CPI chainrings!

grizzly59

Cassette & chainrings don't look bad. First step, check your chain with a steel rule. You can't check anything with a worn chain. With a new (ish) chain, you can check the cassette and chainrings. Don't ride with a worn chain.

Here's a start:

dedhed

YOu don't need that exact chain ring. 36T, 104 BCD
If it was me, I'd drop a new cassette and chain on it.
New chain, cassette, and chain ring you'll be under $50, peace of mind - Priceless.
Cassette tool, allen wrenches, chain tool, chain whip. Bike Co op nearby to assist and use tools?

https://www.jensonusa.com/Shimano-De...PEED-Chainring

https://www.jensonusa.com/Shimano-CS...Speed-Cassette

gnrboyd

Thanks for the input everyone.

I have checked the chain (which has about 4K on it) and it has zero stretch so far. The last chain was a KMC and I changed at about 8K. It was barely getting to the recommended change point (stretch) even after that many miles so I replaced it with the same model since. I didn't know really how to look for wear on the cassette or chainring other than visual inspection so the video provided some good tips. I will have to put everything back together, however, in order to check it.

I have all the tools to change everything that I have been acquiring over the past couple of years. I just need more knowledge of when I need to use them. I am not aware of any bike coops around but might check into that.
If I use a different model chainring, will there be any difference in the shifting. It not, I wonder why they make so many models. Bike parts are crazy stupid if you ask me.


I guess don't have any issues with shifting, skipping? So, obviously you would keep riding using these components as is.


I think, I will put everything back together and check the drive-train as instructed in the video. Even if it is all good, I will probably go ahead and buy the components and have them ready when I decide the time is right. Thanks for your help everyone.

grizzly59