I have a Jamis Coda Comp 2012 that I purchased used from an estate sale.

Jamis Coda Comp (2012) Specs

I want to change it from 3x9 to 1x10 38T 11-48

Here is my plan:

• Microshift Advent X 11-48 cassette
• Microshift Advent X Trail Trigger Pro Right Shifter 1x10
• Microshift Advent X Rear Derailleur 10-Speed Medium Cage with Clutch
• KMC X10-116L, NP/BK 10-Speed Bicycle Chain
• 38T front

Questions:

Should purchase a new 1x10 crankset? If so can you recommend a brand/model?

Or should change the chainrings on this current Shimano Acera FC-M391 crankset?

If so, do change the middle one? How do I know what bolt configuration to get? Can you recommend a 38T chainring brand/model? If I need shorter bolts where do I purchase them?

Thanks!

You will need a new Bottom bracket as well. The spec says 68 x 110.5mm but it really is a 68 x 122mm wide square taper.... I know because I had one... fairly nice riding frame...... but it was stolen.
Suggest maybe another option... buy a new bike.

Half the fun is customizing.

Good option for you. But OP chooses not to.

I love the bike. Steel frame and caliper brakes, I just want to simplify the gearing even more so.

Will I need to change the BB size or would a 1x10 crankset be already the proper chain line?

Not all Cranksets are created Equally.

you should start by listing the cranksets you are considering buying.

your Acera crankset has a 50mm chainline specified... going from 9 to 10 gears in the back won't alter that.

just remove the inner and outer chainrings and check the chainline to the middle chainring to see that it work fine....an increase from 36 to 38 teeth shouldn't cause interference at the chainstay... the diameter increases 3/4", so the teeth will be 3/8" farther to the rear once the 38 Tooth chainring is mounted to your Acera crank.