Cog threading question...

Excuse the multi-forum cross post but, HELP!

So I got an 18t Roselli cog today, to put on my Zeus rear hub. The threading on the cog is 1.37 x 24TPI and I was assured the size was correct by a suitably reputable source (Shifter Dan).

The problem is this: When I start to thread it on, I get about half a turn in and it catches. I put a little pressure on it with my chain whip, thinking there might have been a minor deviation in the threading or something. Problem was, it didn’t get easier to turn.

When I removed the cog, it looks like it’s eating the hub threading alive. Nasty burrs and bit of metal coming off. It’s only on the start of the hub threading, as I didn’t go any further than that, so I haven’t trashed the hub.

I’m guessing it’s not really a good thing, but this is the first fixed gear I’ve built so I’m no expert on the matter.

Am I doing it wrong?

Any help is much appreciated!

What cog did the hub originally come with?

It didn’t come with a cog, I bought the wheelset NOS from an LBS.

You may have just cross threaded it by screwing not 100% straight (Craig?). Your LBS may be able to clean up the thread for you.

(edit: Des already asked about old cog - duh)

sounds like there might be a burr in the threading of the cog.

  • Joel

The threads on a zeus hub should be standard so I don’t think it’s a problem with the cog.

Either you cross threaded the cog in the first place or there might be a burr somewhere like pod suggested. You should be able to thread a cog into a hub by quite easily by hand. Did you apply any grease on the threads?


Is grease on the threads, GOOD or BAD?

Grease = good!

Thanks guys. I think I did seat it badly the first time. I’ll take it into the LBS and see if they can clean up the minor messy bit at the start of the thread for me.

Ok so I took the wheel and cog into the LBS today. John hit it up with a thread file, and it was still catching about two turns in. It was a bit sketchy, but it was threading on dead straight so he just greased the shit out of it and used a chain-whip to get it on. It wasn’t cross-threading, but we think the threads on the hub were just a little high for it, so the cog was shearing off the tops.

Kinda scary, but it’s on now and hopefully it’ll stay on (and hopefully I’ll still be able to replace it).

Fingers crossed.

might have been the old 1.375" vs 1.370" ISO vs English thing.

Damn Europeans have to make things difficult for us eh chaps?

  • Joel

There were super-fine strips of metal coming off it, so that sounds like a reasonable explanation. Cheers!

yeah the English thread is 1 and 3/8" (1.375") but ISO (European) doesn’t use fractional inches so just decimalised it to 1.37". Makes for a tight fit but still compatible.

  • Joel

Interestingly, the Campy lock ring threaded perfectly.

I guess Zeus use the campy/ISO lockring threading rather than the english one.

  • Joel

Yeah, just seems strange that they’d mix and match.

Anyway, the bike’s up and rolling and my legs are suffering suitably from the breaking in. I’ll throw up some photos in the next few days, it looks very sweet.