I'm renovating an older bike. I took the 6 speed freewheel (Shimano mf-tz20) off because it was rusty, disassembled, chucked the parts in vinegar overnight. The rust came off, but so did the goldish tint of the cogs. I'm assuming the steel cogs had some coating applied to them to prevent rust/harden, I'm not exactly sure. My question is, what kind of coating did I strip off the freewheel, and what can I do to prevent rust on the now bare steel surface?

shimano mf tz20

  • Just use it till it does. Chain lube and WD40. – paparazzo Apr 9 '17 at 19:47
  • 1
    If you take a look at images of the specified model, you'll see the cogs have this gold-ish factory tint. – András Szilveszter Apr 9 '17 at 20:00
  • If you're really worried about this, I'd just spend the 8-10 bucks on a replacement freewheel. I'm with @Paparazzi on this, sans the WD40. – Batman Apr 9 '17 at 21:22
  • 1
    My guess is that moreso the grease and what not in the bearings of the freewheel may have degraded from this vinegar soak, unless for some reason you fully tore down the freewheel and repacked it (which is likely more expense/work than just getting the replacement). – Batman Apr 10 '17 at 1:02
  • 2
    You can buy 20 of these freewheels for about 1 high spec ultegra cassette. Sometimes its worth replacing wear parts with new ones. Chains and freewheels are not worth the time to salvage. – Criggie Apr 10 '17 at 3:51

Baked on grease can look yellow or the manufacturer might have coated it with something. In this case, it looks like the manufacturer gave it a light coating.

Normally the lube from your chain (especially if you use a tacky lube) is enough to prevent corrosion. But if you're worried, why not just give it an extra coating of silicone oil.

For bare metal parts, I also use Boeshield, figuring if it's good enough for BOEing to SHIELD aeronautical parts from corrosion, it's good enough for my bike. I use it on places like hex bolt heads which seem to attract corrosion but you could also use inside your cassette.

Fineprints: But (along the lines of what @Criggie points out) it might be cheaper to buy a new freewheel than a can of Boeshield... Another side note is that using an acid to strip rust can be a bad idea because it leaves the exposed metal in a particularly vulnerable state for corrosion. Because rust on the sides of the sprockets really doesn't hurt you, I would have just degreased with a citrus degreaser and left the rust alone -- or bought a new freewheel.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.