parksung

When I get off the seat and peddle harder, I notice a grinding on the chain, as if it might even come off.

Does this call for a new pulley, derailleur, etc. or just a tuneup to tighten some parts?

AdamDZ

You should post this in Bike Mechanics subforum. Does it happen in any gear/all gears?

Adam

parksung

thanks, i didn't see that and was wondering about a repairs section. i usually ride harder in 5th gear so only notice it in that one.

AdamDZ

Check if it happens in all gears or just some. Maybe it just needs some cleaning and lube. And yeah, you'd be better off re-posting this in the Bike Mechanics forum.

Adam

Bikewer

Under very hard pedaling, it's possible for the frame to flex slightly and let the chain rub against the derailleur cage. This is fairly common, especially if you're already in higher gears. You don't tell us what you're running; what sort of crankset and what gears you are in when this occurs.

BarracksSi

Yup, this is more of a question for the Mechanics forum. But anyway...

It's more common for the bottom bracket to loosen and let the crank wobble -- or for the crank to loosen and start to come apart.

I had a Cannondale CAAD8 that started to do it after 500 miles, and it's one of the stiffest frames out there. What happened was the crank had a press-fit design that held the spider onto the spindle, and it started to work itself loose. I took it it under warranty, and they offered to replace it with a crank from a different manufacturer. The new one didn't wobble one bit over the next 3000 miles I owned the bike.

In the meantime, the front derailleur can be getting out of adjustment. Check here:
https://www.parktool.com/repair/readhowto.asp?id=75
https://bicycletutor.com/adjust-front-derailer/

Kimmitt 

First answer for any drivetrain problem is Triflow.

BarracksSi

Suggesting Triflow for a grinding drivetrain is like suggesting aspirin for a grinding knee. You might quiet it down, but you won't be fixing it.