I'm replacing an Astabula Crank that I have on my Vintage Sears 10-speed. I was wondering if the bb shell of the frame is threaded. If not, do I have to buy an adapter for the shell? A friend of mine gave me a pretty much brand new Truvativ Square LE BB-07 108mm, and I was wondering if I can just put it on and it'll be fine, or do I need an English to Euro conversion?

One-piece shells are unthreaded, and they are of a much larger size. You'll need an adaptor or conversion kit to make the frame compatible with 3-pc cranks. What's wrong with the Ashtabula crank?

https://harriscyclery.net/itemdetails.cfm?ID=1335

limited gear ratios and pedals.

"Be the first kid on your block to put a Dura-Ace crankset into your Schwinn Varsity!"

Yes, and they're heavy and ugly, too; but they're also durable, simple to service and fine for commuting and riding around. I was wondering what was the issue with the OP's particular crank, not the issue with 1-pc cranks in general. As it is, Cbb makes no mention of a replacement crank, only a freebie sq taper bb.

Will that actually fit on my bike?

Well another friend is also willing to give me his old crankset with a little higher Ratio. So I've pretty much gotten all the materials to replace my old one-piece (Except now I need to buy a conversion kit)

Based on many threads posted here he won't be anywhere near the first. I expect someone somewhere has installed a full Super Record 11-speed group on a Roadmaster.

If it's old, will fitting a new crank be worth it?, is the chain even compatiable with the new crank, if not, then you need a new chain, maybe, free wheel block / cassette; thinking you could quickly spend more than the bike is worth bringing it up to a spec lower than a new one

3 piece adaptors will fit just fine. I had the local shop install one for me. The bottom bracket looks a little funky installed into the adaptor, but I have no complaints as to how it works.

Primary reason for my change was to save weight. Secondary reason was to be able to change gear ratios.


Tom

My bicycle is pretty much a fixed gear bike right now. Everything is new, chain, rear cog, wheel etc. The only thing original on this bike is the frame itself (yeah) and the cranks. The cranks are a 3/32 while the chain and rear cog is already a 1/8.

I've already dumped a good amount of money so far, and I think it's worth it since my friends have been helping me out with getting deals and selling/giving me their parts. Plus I get to enjoy building up my own bike.

used to have a Tubular OPC, 25 years ago was actually quite decent..
still need to use 1/2" pedals , though there is a 'knee saver'
1/2" to 9/16 adapter , now .. widens the Q [feet further apart], of course.

fine for single speed or rear hub gears. internal or external .

OPC's Bearings are cheap and races bang in and out easily.

I'd say if you want aluminum Crank arms .. the Adapter rings
to make it possible to fit a regular type BB is the way to go.

I did the same thing with a '71 super sport. I used a Sugino RD2 165 crank and it worked just fine. Of course, you will need a bottom bracket of the correct length to get your chainline right.

Tom