So I've currently got three-piece cranks running on unsealed (cup/cone/retainer type) bearings in an American bottom bracket shell.

The cup and cone on the drive side are getting rather pitted and the retainer isn't doing as much retaining as it should be anymore, so it looks like it's time for an overhaul pretty soon. In the meantime it's at least running on fresh grease with all the metal shavings cleaned out, so I've probably got at least a couple of weeks up my sleeve.

Since I'm going to be replacing the cups anyway I figure now's as good a time as any to upgrade to sealed bearings. I've been looking around online and it looks like sealed bearings are readily available for an American BB, though I'll need to replace my spindle as well.

Now, I'd rather not replace my cranks if I can possibly help it, cause really there's nothing wrong with them. Which means I'll need to buy a spindle that will match the cranks.

This is where things get difficult. As near as I can tell from reading around online there's only a couple of crank/spindle interface standards for road/mountain bikes, but BMX cranks seem to have as many standards as there are manufacturers, and nobody's writing much documentation about them (or not that I've found, anyway). I'm hoping someone can tell me what the type I have are known as, so I can make sure to buy compatible parts.

The cranks are held on by an allen bolt that screws into the end of the spindle, and also by a pinch-bolt on the crank. Here's a pic of the end of the spindle with the crank removed:



Thanks

I'd recommend going to an LBS that has a lot of BMX bikes. It looks familiar but I can't place it. The LBS can pore through their QBP catalog and find whatever it is. If you have a crank brand or model number etc it helps.

I have some proprietary BMX crank/spindle setup on an exercise bike and I have no idea what they are. I just bought them together.

cdr

Reasonable suggestion, though when I can I prefer to do my research before wandering into a store. That way I get the opportunity to shop around a bit first, or order the part through my preferred LBS (who otherwise don't have a lot to do with BMX), rather than feeling pressured into buying from the first place that has a matching part.

Still hunting around online myself for information about these, but if anyone recognise them or can at least point me in the right direction please sing out.

They look like Industry Rocker cranks. You'll likely need a 28tpi 3 pc american BB set. Those are hard to find these days, you might have to settle for another unsealed OEM BB.

Found these googling for "industry rocker": https://www.danscomp.com/455241.php

A bit hard to tell for sure from the small picture, but they look like they've got 12 small splines rather than the 8 large splines like I've got. Thanks though. I'll keep poking around and see what turns up...