Slipping Cog? Loose Crank?
 

So I've been riding my fixie around and recently it's developed some odd problem that I can't diagnose. I built the damn thing myself, so you'd think I could find the problem, but nooo.

When I go hard forward, like out of a green light, the pedals slip forward about 15 degrees. They're fine until I do the same thing in reverse, skip-stopping or even just a hard stop. Then they slip 15 degrees backward.

I tightened the lockring and I swear that's not the problem. My left crank arm is losing life quickly, but that doesn't seem like it's the problem in this case either. Any ideas? I want to ride without fearing for my life.

Sounds like the cog/lockring to me.

sounds like the lockring, make sure that your cog is all the way tightened before you tighten the lockring. If the moving keeps up, the cog should move so easily that you can move it by hand. A cog this loose can lead to stripped threads.

So get out that chain whip or use the rotaflex method and then crank on the lockring with a lockring tool (a screwdriver can only do so much).

or go to your LBS. i still have no idea if i'll ever trust myself to put a cog on.

Ha, I didn't read the user name. I'll have my basic tools with me (lockring/15mm wrench/multi tool) toorrow and I can see if I can't crank it down for you.

sometimes the lockring will bottom out before hitting the cog,
so no matter how much you tighten down your lockring you
can still get some slippage.

you may need to put a washer,(spacer) between the cog and lockring.

the same thing happened to me friday it turned out the cog was slipping and some of the threads stripped

It seems like the initial instalation of the lockring is never tight enough, you need to ride arround a little, then you can get it to the proper tightness.

It seems like a pretty easy task if you have a chainwhip and lockring wrench...

Even chainwhips are overrated. Rotafixa for life, *****es.

I've installed two (2) cogs and lockrings, both with the rotafixa and hammer+screwdriver lockring wrench. Both have worked fine.

I agree that chainwhips are overrated. However... after getting a lockring tool (to replace hammer+screwdriver), I will never go back, I can crank down way more on my lockring these days.

Thanks everyone...see you tomorrow for your tools

ha! my local bike shop guy--the kind of guy who fixes things with hammers and duct tape--loves the hammer-and-something-else lockring wrench. i love it too.

this is a good time to reiterate proper cog and lockring installation:
1. grease threads.
2. thread cog on gently.
3. chainwhip or rotafix it on. get firm and strong on that mofo.
4. put a lockring on. tighten it, firm and strong again.
5. go for a ride. mash up some hills but apply NO backpressure (rely exclusively on your handbrake to stop).
6. stop and tighten your lockring again.

You don't need a dedicated track hub lockring spanner if you have a (fairly common) Park HCW-5 bottom bracket lockring spanner. The three-pronged end actually works fantastically for tightening fixed-gear hub lockrings (or at least it does with my Dura Ace lockring). It's a bit of an odd usage, but it's treated me very well so far. The other end of the tool has too large of a radius and will slip off of the lockring and chew up your knuckles and round off the lockring's groove.