Weird- must have cached somewhere

bah bottom brackets.... So this downhill tank bike thing has a "truvativ howitzer" bottom bracket. Its definitely threadded, with octalink splines, but I have no idea what standard it is.

Even sram's product page won't tell me what standard it is.

sram.com/truvativ/products/truvativ-howitzer-team-bb

looks like BSA to me

the Q&A on chain reaction says's it's a 73mm BSA threaded.

but not standard octalink and needs howitzer cranks of some flavour

I have the cranks, which came off with octalink tool, and they look similar.

My chain keeps popping off the bike while riding and it skips a half a turn or so and then pops back on(I think) this is what is happening. Anyone have any idea how to fix this?

ping me if you have any idea, I might be able to get a video

I have considered making it a single speed which I believe would stop this issue

@William no idea, but I'd check the wear of the drive train. At least the chain should be easy to verify if you have a tool for measuring lengths with good precision (1/10th even 1/100th of a millimeter).

Hand built wheels? They seem perfect. Why so cheap?

@William does it pop off at the front or back? Does it happen in the workshop or only when riding? How worn is the casseette/chain rings ? Does it happen in any gear or just a specific one? Has it got worse slowly or started suddenly?

@gschenk What's that about hand build wheels in relation to?

@Criggie I am not sure it only happens at full speed mostly. Only when riding. It is a fairly old bike for sure. I just leave the bike in one gear in fact the gear changer doesn't work properly(I don't use it). Its a flat ground single speed mountain bike except the gear switcher is still on it.

If it's at the front, it sounds a lot like the teeth on the chainring are worn -- do they look sharp and pointy?

Sometimes I'll go down hill but never up

They look fairly normal. Its not rusted or anything for sure

I'll grab a picture later when I get home. I wonder if its the added weight from the airless tires and rack I put on it.

The key question is sharp and pointy, often described as looking like shark's fins. If so, the teeth are worn and the chain can slip past them when you pedal hard. A picture would help, yes.

Especially as one tends not to notice the change over time, so they can keep looking normal even though they're not any more.

I doubt it's added weight. Unless maybe it was going to start next month but adding the weight meant you had to pedal harder so the symptoms showed up earlier.

Oh sorry. The link was somehow lost

:47273560

The TradeMe.nz posting read as if they were and built. In particular Mavic rims with Shimano hubs?

Oh yeah I got them

@William sounds like its time for some bike maintenance. At a guess, fixing this problem will probably involve replacing cassette and chain, and you may as well fix the derailleur at the same time.

@gschenk the wheels are in the photo above, fitted to my Raleigh Arena.

I don't care about the derailleur though. I don't use the other gears

I need the time to make it single speed, might fix this issue

well do that too, and your problem may resolve.

You posted on Strava when you went there.

William, if you don't use the other gears, perhaps you wore the sprocket early. Compare the teeth with other sprockets teeth. Same shape?