Singlespeed & Fixed Gear - Moderately (at least) sticky hub threads

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Blue Motobecane
10-09-10, 09:29 PM
Hi everyone,

I figured I should ask about this now rather than strip the threads of my hub. I have a 1973 Motobecane Mirage that I am converting to a fixed gear. It came with a Japanese freewheel, so I was hopeful that an ISO cog would fit. To make sure, I tested it with a Dura-Ace cog borrowed from a friend and it went on effortlessly. The lockring I bought for it also slides on all the way without any effort.

However, the EAI cog that I purchased to use on it does not fit perfectly. It slides most of the way on but then encounters resistance with 4-5 mm of space between the hub flange and the cog. I am sure I could force it, but obviously don't want to strip the hub threading. Are there really differences that significant between the nominally identical threading on track cogs? Do I have a defective cog?

Has anyone else had a problem like this before? Your thoughts are appreciated.

Squirrelli
10-09-10, 09:41 PM
Cogs should go on fairly easy, don't force it on. Clean the threads of both cog and hub, grease then reinstall.
FastJake
10-09-10, 10:12 PM
Cogs should go on fairly easy, don't force it on. Clean the threads of both cog and hub, grease then reinstall.

I agree. Also, aluminum hub threads are pretty easy to strip. If you have to force it on, chances are the cog's steel threads will rip up your hub. Best to get a different cog if yours doesn't work.

blickblocks
10-09-10, 10:33 PM
All of the cogs I've installed had a moderate amount of force needed to thread on fully. As in, you couldn't get them threaded on by hand, but went on fine when rotafixed (I don't use a chainwhip).
Blue Motobecane
10-09-10, 11:06 PM
All of the cogs I've installed had a moderate amount of force needed to thread on fully. As in, you couldn't get them threaded on by hand, but went on fine when rotafixed (I don't use a chainwhip).

Really? That seems like it shouldn't be the case, even if there are slight differences in thread tolerance. I know it might be fine if I force it on, but I also know that I shouldn't have to and won't know until it's too late whether I'm ruining the threads. After playing with it some more, I think I'm probably better off just returning the thing and going with Dura-Ace . . .
Squirrelli
10-09-10, 11:12 PM
EAI and Dura Ace cogs are have the same thread pitch and both of them are quality made cogs.

Inspect the threads on your hub and cog to see if they are damaged/crossed.
Blue Motobecane
10-09-10, 11:42 PM
EAI and Dura Ace cogs are have the same thread pitch and both of them are quality made cogs.

Inspect the threads on your hub and cog to see if they are damaged/crossed.

Same nominal thread pitch, but it's clear there's a difference. I have a D-A cog, the new EAI cog, and a new lockring sitting next to me. D-A cog threads on with no resistance, lockring threads on with no resistance, EAI cog has so much that I don't think I could hand-tighten it.

Definitely no cross-threading or stripping on the hub, and the cog looks fine.

Since it doesn't seem like this is a known issue with EAI cogs, I'm not really comfortable torquing on a thread that I can't hand-tighten.
blickblocks
10-10-10, 12:19 AM
Even if they use the same pitch, the thread profiles are probably different. I wouldn't worry about it.