Hello,
I have a 9 speed Specialized Rockhopper mountain bike. I bought this on craigslist. I don't know the exact year. I don't have the correct crankset. It creaks while pedeling. I replaced the BB and it was quiet for about 1 month. Do I need a 9 speed crankset? If so, https://www.amazon.com/gp/product/B00...A16QDZ1XG7GVFM
will this work? 170mm or 175mm, I don't know!
Thank You!

It's a Rockhopper, not Hardrock, you can see that by looking at the top tube.

For the year, thinking it's around 2000/1, you can research Bikepedia for the exact year 2000 Specialized Rockhopper A1 FS - BikePedia

For the crank, you need to ID what you currently have, from the age, it could be Square Taper, ISIS or Octalink, for length, if what you currently have works, choose that length, it should be printed/stamped on the back of the crank, probably near the pedal hole

When I bought the bike...the original crankset teeth where so bad, I removed the crankset and threw it away. I am learning as I go along. It's a square tapered BB. the original BB UN40 I just replaced to a Shimano BB UN 26 68mm 110 mm. I have a cheap 7 speed crank on the bike now. It's been working just fine until about 1 month ago. 22 32 44 crank needed, from the amazon link, I don't know if I need the 170mm or 175mm?

170 or 175mm is totally up to you.
It's the length of the arm.
Taller people use longer arms than shorter people.
I have a bad knee, so I use 165mm.
If you are under 6', you probably want the 170mm.

One final question please....Do I really need a 9 speed crankset? Do you think the creaking noise is now coming from the wrong crankset? Thank You!

My thoughts are you should take your bike to a bike shop and have one of their mechanics take a quick look at it. Shouldnt cost anything and they should be able to set you in the right direction. Your posts are unclear in describing the problem imo, and since you dont seem to have a of experience with crank sets/gears i dont think you're gonna figure this out on here. Could end up replacing parts and replacing parts without fixing the problem..

68 X 110 bottom bracket doesn't sound right to me. Are you sure it's not 73 X 110? That's what I would normally expect on a mountain bike. How much clearance do you have between your left side pedal and the chain stay?

How did you install the bottom bracket. The torque spec for BBs is about 30 ft/lbs. That's a pretty good amount. Imaging a 30 pound weight hanging on the end of a foot long wrench. If the bottom bracket isn't tight enough, that'll definitely make a creaking sound. Crank arms need 30 ft/lbs of torque too.

I wouldn't worry about the crankset. I don't see how that could be causing your particular problem.

I appreciate your comments...however the problem is strictly in the drive. I have already replaced the bottom bracket, chain and cassette. The only thing remaining is the crankset. I would like to know if other members have replaced a 9 speed crankset with a 7 speed and if it worked for a long period of time without creaking.

I brought the bike in a bike shop to remove the original BB. It took two people to remove the original and a pipe. I did not use a torque wrench to install the new BB. I bought the correct tool and just snugged it up. I do the same with cranksets.

I still have the original BB. Shimano BB-UN40 68 1.37 x 24

If it took 2 people and a pipe to get the old bottom bracket off, what does that tell you about how tight bottom brackets have to be?

So, back to the bike shop to re tighten?

Thank You!

I agree about checking the BB. And yeah, the shop should be able to tell you pretty quickly what's wrong. Have you tried checking for play in the BB, btw?

10+ year old bike & square taper, been there, done that, more like corroded/seized in, than done up exceptionally tight

If your 7-speed crankset worked for a while changing to a 9-speed one is likely unnecessary. I think that you need to invest in/borrow a torque wrench and tighten things properly. "Snug" is not going to cut it, especially with a bottom bracket.