rat_factory

i'm trying to grind off the rivets of my ~'97 HG-30 cassette. I am trying to separate the cogs so i can clean the rust of the cogs as the bike was sitting outside for some months. I remember reading that you grind the rivets off the largest cog to separate them: https://www.sheldonbrown.com/k7.html. I did this and they are stuck. I pried a little with my screwdriver, but i felt flex and maybe even bending of the teeth.

Has anyone done this before and how did you remove the cogs from the rivets?

Pic:

mechBgon

Now just punch them out using a punch and hammer, or a nail and a rock, etc.

gorn

Maybe a bit of penetrating oil on the studs then take a nail punch or a small bolt and hammer the studs out.

古強者死神

yep all the above, maybe drill them out as a last resort?

Mothra

I've never had a need to drill them out no matter how badly they're rusted. The actual contact surface-area between the pins and the cogs is minimal. Just they the cogset over a vice so that the pin will fall into a 1/4" gap in the jaws. Then use a punch to tap the pins out from the front-side.

Little Darwin

That rust would not impact functionality, so you are bviously doing this for looks... this is best accomplished by buying a new casette.

For functionality, a few minutes with a wire brush and then some good lubrication will make it as good as new.

Al1943

It's not worth it if you are just trying to get rid of the rust. It's best to have the cogs pinned together so that the torque is carried across the larger cogs instead of having individual cogs digging into the hub shell.

Al

rat_factory

why would the cogs dig into the hub shell? you mean the splined cassette body? i remember UG stuff had splines and just the outer cog screwed on holding everything else in place. I never had any dig marks there, but it is something i will look for next overhaul. perhaps the newer cassette bodies do not compensate for individual cog torque like UG. i'm fixing this bike for my girlfriend as a backup commuter and am not going to rack up a bill (in addition to other stuff) with a $20 cassette. i think its sloppy to leave rust in a rebuild too and i'd rather just strip the rust off with a brass brush. and the rivets just seem to fall out almost if you wiggle the cogs and twist them back and forth.

Mothra

Here's what can happen if the cogs aren't pinned together:



All of the load from pedaling forces is concentrated on a tiny 1.7mm wide spot on the freehub body where the splines on a single cog touches. With the cogs pinned together, the load is spread out across many gears and not concentrated on a single one.

joejack951

That rust will come right back if the bike gets wet since now all the rust-preventing coating is gone. Unless you replace it by either sending the cogs to an electroplater or spraying them with a zinc-filled paint (although this would probably cause other issues so I wouldn't recommend it) you are wasting your time.

rmfnla

Except that 9 & 10 speed cassetts are no longer pinned together...

I have broken old cassettes apart many times to get specific-sized cogs to build custom cassette combinations and have not seen "digging" except on Al hub bodies (rare).

OP: you are on the right track. Support the cassette on something stable like a bench vise & give those pins a good whack with a decent hammer & pin punch; they'll come free (although I agree w/ the posters who suggest a new cassette; the rust will probably just come right back unless you keep it really well-lubed at all times).

joejack951

Maybe not all the cogs, but at least the three big cogs on my Ultegra 10 cassette are pinned together (can't remember if it was 3 or 4). Makes sense since for a given chain tension, those cogs exert a much higher force on the freehub than the little ones.

I haven't been working on bikes long enough to say this with any certainty, but I would think digging like shown in that picture would only occur if the cassette was not properly tightened onto the freehub (too little torque).

rat_factory

i got the rivets out basically by wiggling the cogs firmly. I've stripped rust from many freewheels with a brass brush and rust never returns even in wet weather, although I lube the chain regularly. I think the brass is hard enough to strip the rust, but steel is obviously harder than brass and is not removed in the process. The cassette originally had no zinc or nickel coating anyway.

As far as the digging issue, Sheldon only says that occurs on alloy bodies, but i think i will try to find a long hex bolt or something with a shallow head and nut to secure them together, or I could hand rivet them with some large gauge wire. Combined with 40nm lockring I don't think I will have a problem.

'nother

Hmm, I can't say you're wrong, but I get the idea from reading Sheldon Brown's site that this sort of thing is caused by using aluminum freehub shells, not loose cogs: https://sheldonbrown.com/k7.html, see "Non-Shimano Hubs", towards the bottom. He is an advocate of loose cogs (or at least, not an opponent), and he should know.

Seems like if the cassette is properly installed it shouldn't matter.

'nother

That is a little bit different case but the point is still relevant. Shimano's reason (marketing reason anyway) for pinning the cogs together is weight savings, and they're not pinned together like the OP they are on a "spider". Most Shimano cassettes are sold with many loose cogs. It simply doesn't make sense that they would sell something like that if there were a danger of them digging into the freehub shell (Shimano shells anyway).

Also seems to me that the smaller cogs would experience higher torque (per unit of area) than the larger ones given the same chain tension. Anyway the photo seems to show damage around the middle cogs. I am not really buying the "loose-cogs-are-bad" argument.

joejack951

What do you mean by "higher torque (per unit of area)"? My comment was based on torque = force (chain tension) * radius of cog. Assuming a rider can generate a certain amount of force on the cranks, this will apply a certain force to the cog. A large cog has this force applied at a greater distance from the freehub so the torque generated is greater.

douglas fir

The older cassettes were bolted together. it takes a 3mm or so nut driver to remove them. If it really was a rivet- punch it out. Soaking them in diesel ahead of time sure helps.

I've rebuilt many, getting the gearing I want

douglas fir

if not, just punch them out after the grind job- which looks good BTW.

HillRider

Are you sure they are rivets? Most of the cassettes I've taken apart either needed a 3mm box or socket wrench or a 1.5 mm allen key to remove the retaining bolts. Maybe the reason you can't punch them out is that they are threaded in.

'nother

Sorry, I see what you are saying. I was thinking more force on the smaller cogs because of the smaller number of teeth, more revs per pedal stroke, etc. (which is why smaller cogs tend to wear faster). But anyway: the photograph shows damage to the center cogs, which doesn't really support either of our ideas and which was my point anyway

I was thinking that, too. I have a couple if cassettes which on first glance look like rivets but are actually a small hex head. If the heads have been ground off, there may be no choice but to drill (at least through the first sprocket...I don't think the threading goes all the way through; could vary depending on who made it). But just think of the picograms you can cut if you drill it out with a larger diameter

rmfnla

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joejack951

No, they don't exert the same force. Say your big cog is 3 inches in diameter and the small one is 2 inches. Your hub shell is 1 inch in diameter. In order for the hub shell the not move in relation to the cogs the force exerted at the hub shell must equal what's exert at the cog. So If you exert a one pound force on the big cog you get 3 in.*1 lb. = 1 in. * X lbs. X must equal 3. Now you apply a one pound force on the small cog. 2 in. * 1 lb. = 1 in. * X lbs. X must equal 2.

rmfnla

Makes sense; what you're describing is leverage (or torque) which I guess is why the larger cogs on newer high-end cassettes are on a carrier (and why that photo shows the digs in the middle, the largest individual cogs on such a cluster).

Thanks for the physics refresher.

Zouf

Actually, the reason the larger cogs are on a carrier (a.k.a. spider) is to lower the weight. Most cogs are steel (except outlandish Titanium ones, and crazy-nuts aluminium ones) - mostly to resist wear. The larger cogs wind up carrying a lot of steel; using an aluminium spider with steel cogs gives the best of both worlds.