Thanks for taking the time to read through this!

I had a pedal strip out of the crank arm while under load on my 2011 Trek 3900 Disc MTB. That was a mystery of it's own on a bike that does have fairly heavy mileage, but I digress.

I am new to this whole bicycle mechanics thing, but have some experience with a total rebuild of another, much older bike.

After pulling the crank arms, I cleaned up the bottom bracket and took a look at it's condition. It's tight as far as any slop either end-to-end or up & down, even when using the crank arms to lever it around. What I feel when I rotate the spindle is considerably more "gravelly" than the silky smooth feel of the cup/cone/loose ball BB that's on my older bicycle. When I put the crank arms on the BB turns very freely and the cranks swing easily with not too much noise....but again, more noise than the cup-n-cone one. Is that "normal" for a cartridge type BB? Or..."as long as it's torn apart..."

One more quick question on this repair, please. I went with the same model/brand of crankset, but went 4 teeth more on the two smaller chainrings and 6 more on the largest. Is there a formula for lengthening the chain....or will the old number links + 6 work?

Thanks again!