OK so I am going to 1) build a single speed and 2) potentially reconfigure another bike to be a 9 speed (RD only).
for #1)
What is a good road single speed chain ring?
Will that fit on my existing crank (old Suntour) I am assuming it would take the place of my 42.
Does anyone manufacture a blank ring (akin to a rock ring) that will fit on my crank in place of my big ring (53)?
for #2)
Do I need a new crank or can I reconfigure as above using the existing crank?
with a single front ring should I be using a short arm RD?
Your crankset ought to be fine. I’d assume it’s 130 bcd, unless it’s a triple, in which case it may be 110. There are plenty of good chainrings for either - Surly and Spot Brand will both run about $40. Spot makes a decent singlespeed guard that’d work. I’ve got one on my ss mtb that I like just fine. Might be a chore finding a guard that’ll accommodate more than 44t, though. Jenson and Speedgoat, among others, are good sources for ss parts.
Depends on what sort of riding you’ll be doing, but a good starting point for a road single would be around 70 gear-inches (you can play with ratios using Sheldon Brown’s gear calculator). For a mtb, that entirely depends on terrain. I’ve got mine set up with a 34x13 (68 gear inches), which is a bit tall for steep or technical trails.
As for the rear der, you ought to be fine with either long or short cage.
Also, some people have suggested that you can just cut or grind the teeth off of a standard chainring to make a spacer. I used some spacer washers from Harris Cyclery on my SS to create a nice chainline. Like this.
Guess I have an old bent ring around somewhere if it fits. Turns out that the bike was only made 1 year so I don’t want to trash the parts.But I thnk that it will be a good one as it has thumb screws to adjust the dropouts.
I’ve seen 42/44T chainguards for 130BCD before, marketed for cyclocross. If you run a 110BCD crank, then you can get bigger outer guards (48/50T) intended for MTB DH.
