How to take care of single freewheel sprocket?

I've got a new single-speed Bianchi that has a flip-flop hub where the freewheel side (the side I actually use) is a Shimano SF-MX30 single-sprocket freewheel. That is, the freewheel mechanism is in the sprocket that goes on the hub, rather than being in the hub. Anyway, if you look on the net at a pic of this item you'll see that there's a really tight clearance between the part that spins (the black middle) and the part that doesn't spin when you coast (the silver sprocket). How do I keep that from gritting up and destroying itself? There's no seal there of course. Just a spinning metal piece and a stationary metal piece that almost touches.

 

Short of disassembling the unit, it can be cleaned and lubricated the same as any freewheel. Use light aerosol lubricants such as WD40 or Kroil penetrating oil to flush out old oil and dirt. This can also be done using a parts washer or kerosene bath. It will not be a perfect cleaning, but far better han none.

Lubrication can be done by spinning the freewheel by hand while submerged in an oil bath (messy, but thorough) or simply allowing oil to seep thru the gap in the body.

 

I'd just keep the external clean and maybe drip a little oil into the crack if it starts to freeze up. Otherwise, how much time are you willing to invest in maintaining a part that costs less than $20.00 to replace with a brand new one?

 

+1. Considering the price, and that the cog is most likely going to wear out before the freewheel unit internals, it's just not a part to worry about.

I've got a Fuji Track bike with a similar setup, and put a good quality Surly 1/8" thick track sprocket on the fixed side. Just be careful: if you start riding the fixed-gear side, you may never want to flip back to the freewheel