I am working on fixing up an old mountain bike that I found in the trash. When I took it apart, I couldn't figure out how to get the crank off, so I took it to my LBS and asked them to do it for me. I figured once it was out it would be simple to understand how it worked, but they seem to have put it back together for me and I'm stumped. I googled crank removal, but my crank doesn't look like any of the ones I see in the tutorials.

Can someone tell me what this kind of crank is called, and how you take it apart?

It's known by a few names, American, Ashtabula, or most commonly, a one piece crank.
Here's a tutorial on how to install and service.
https://www.parktool.com/blog/repair-...racket-service
Note, the blue gloves are optional.

Thank you! Do you know if there's a way to do the repair without the SPA-4? Finagling with pliers or something?

OPCs are the easiest cranks to work on, in my opinion. Hardest part will likely be pressing in the bb cups. I use all-thread, some nuts, and huge washers. Good stuff to remember: everything on the right side of the crank is standard threads, and everything on the left side is reverse threads. Also, the crank takes 1/2" pedals. The Park Tool website will cover all of the particulars.

hth

It depends on what the BB's cones are like. Some need pin spanners, others just have 2 big flats which i tend to spin on and off with a decent-sized flathead screwdriver. Yours looks like the type that just needs an adjustable wrench and a flathead to disassemble and service.

Well, I fixed mine back in the 60's with nothing but a screwdriver and an adjustable wrench so no, you don't need the Park tool. However, I don't see a lock nut, and I'm not sure there is a proper lockwasher there. Hopefully you have both or can get them (can always just buy a complete set if the parts are unevenly worn or pitted. See the pic below. Once bearings are greased and the BB is assembled you can just turn down the adjusting cone by pushing around the notches until you feel resistance. Turn it back about 1/8 turn and tighten the locknut. Should have no play but turn without binding (don't expect extremely smooth with this level of quality). If too loose or too tight just loosen the locknut, move the cone very slightly in the needed direction and retighten.

The reason you don't need a tool is that the lockwasher is supposed to have a tab in it that fits into a notch in the spindle portion of the crank. That prevents the cone from turning when you tighten the locknut. As for the cups, nothing fancy needed - even in the shop we generally just used a block of wood and a dead blow hammer.

I've used a hammer and a screwdriver in a pinch.

Overtighten the cone by hand, hand-tighten the locknut against it.

Put a flat screwdriver in one slot of the cone and tap it to unscrew the cone into the locknut.

Voila. A similar trick can be used on 3-piece BBs, if the cup can be turned by hand, using the hammer and screwdriver on the lockring.

Just wanted to say thanks to all! I was able to get it done. To put the cups into the frame I used a c-clamp with some blocks of wood.

I had a small issue in that I had some extra cups that seemed unnecessary. I don't know where they came from. They did fit together with the other parts, but when everything was tightened it was impossible to turn the crank. I removed them based on a youtube video where he didn't have those, and then it worked fine. I have no clue what they were! (They are the small round ones in the 3rd pic of my first post.)

All in all it was kind of a pain (especially getting the cups into the frame) but I'm so happy I did it!

Well, that is why I provided the exploded view that showed all of the parts in the proper orientation. It's only hard the first time.