Are BMX cranks and spindles interchangeable, in the same manner that Square Tapered Cranks and spindles are swappable to adjust chainline, Q-factor, etc?

I have been unable to find good references online.
So far I can loosely assume:

Spindles can be 24, 22, or 19mm diameters
24 and 22 are used by high-end 2-piece cranksets with integrated spindles -not interchangeable
19mm spindles fall into two types, 48splines and 8splines, both of which appear to be standard interface styles, thus spindle and arm combos are interchangeable as long as the spline count matches.

How much of this assumptive knowledge is correct?

Thanks
-bike mechanic, who works on 'normal' bikes and has no experience with these completely different BMX machines.


also, if anyone can suggest some good references for BMX from a mechanics standpoint.... haven't had any good luck online

Nope, its a jumble.

OPC is quite common as is a bunch of 3 Piece combinations ..

What Is the BB shell? OPC or Threaded. ?

The bike in question, is the SE Bikes Fat Ripper 26, a Fat Tire BMX bike

English threaded 100mm shell
cranks are 3 piece 'SE closed-end invisibolt'
the spindle, is 19mm diameter with 8 splines, which seems similar to several other 19mm 8 spline types at least based on photos
Uniquely though, this particular spindle is 200mm long; thus any different crank arms will need to work with it since no other BMX spindle appears to exist in that length

What's the issue with the stock cranks?

I wouldn't assume anything just on number of splines and spindle size. Even 48 spline cranks that are standardized on Profile brand can be wonky when swapping parts around.

Got curious and looked to see what the longest spindle Profile makes and it's way shorter than that. They are into making weird stuff though, if didn't mind paying I'm sure they could make a longer spindle.

If it's just standard English threaded it might be the same bottom bracket shell some of the fat/snow mountain bikes are using. A MTB fat bike crank might work, I think the shell width is 100mm instead of standard 68 or 73mm.

Main issue with the cranks is, they're 175mm long, and everything I ride is 170

The point is going to be moot though, I found out that origin8 makes a cheap 100mm shell square taper BB, who's spindle length miraculously combined with an old (non-fatbike specific) crankset I had lying around, to get a viable chainline on the cranks granny/middle position.


(the bike is a SS, but I'm converting to derailers)

One piece isn't common, at all. Maybe 10+ years ago (and then it was dying off). Even most department store bikes use 3pc nowadays. OP has a handle on modern BMX crank designs.

OP, 175mm has long been the default length for bmx cranks, but as you are attempting to run gears maybe just get a cheap fatbike crankset?