hhk222

I just bought a single speed that's in decent shape but neglected. The freewheel, chainring and chain were rusty. I oiled and cleaned the drivetrain and tested the bike but it rode rough and grindy. I bought it because it was cheap enough and I don't mind a project. After thorough cleaning, I got all the corrosion off the freewheel and chainring and replaced the chain. I bought a new KMC S1 chain, 1/2"x1/8" but it's considerably wider than the chain that was on the bike. I measured the old chain and it's almost certainly a 5-8 speed chain. The freewheel spins like new.

With the new chain and clean chainring and freewheel, tt rides smooth but it occasionally slips a bit under load and, when I first start pedalling, it takes about a 1/4 revolution of the pedal before it engages. I suspect a bad freewheel but I'm wondering if the fact that the previous owner rode with a too-narrow chain has worn the teeth on the chainring and freewheel to the point where it doesn't fit properly with the 1/8" chain. Would that cause the slipping? I'm just not sure. Opinions?

AlmostTrick

If the old chain was "too narrow" it never would have even worked, so I doubt that was an issue. I'd put a new freewheel on it.

hhk222

It was definitely too narrow. I measured the rivet at 2.3-2.4mm with a caliper. That's consistent with a 5-8 speed chain.

stevel610 

I would try getting some oil inside the Freewheel. It could just be a little gummed up and the pawls not catching instantly. I recently had this condition on a bike that hadn't been written very much. After a couple rides the Freewheel started catching quickly.

AlmostTrick

Right, so it was a 3/32 chain which will not properly fit on 1/8" chainrings or freewheels. In my experience not even enough to try to run. Some single speed rings / rear cogs and freewheels are 3/32 which is what yours must be. The 1/8" chain will fit on either.

Mikefule

Freewheels are surprisingly simple and crude mechanisms considering what they have to do. A period of disuse or abuse, some dirt or corrosion, or just a lack of lubrication, and the pawls can fail to engage properly.

The chain thickness is a red herring. A 1/8 chain will work perfectly OK on a narrower chainring and sprocket. A 3/32 chain will not fit onto a 1/8 pair of cogs.

Ideally, on a single speed, you need 1/8 all the way through (chain ring, chain, sprocket) for minimum wear.

In your position, I'd use a thin lubricant and try to get as much into the free wheel as possible, and spin the freewheel backwards, then engage it, and repeat. You may or may not be able to get it to free up.

Failing that, you can pick up new one off Amazon for less than a tenner (UK prices) or under US$20.