Anyone else wear out their primary sprocket?

[drewjet]

While riding today I heard a strange noise. I stop to check it out, think the worst, a blown ESC. It wasn't. The motor sprocket had worn down to a nub. I know that I don't clean my chain as often as I should (read almost never) but I was surprised it went this fast. I do run the bike through some nasty stuff. Soft sand, mud, pretty much anything. It sees very little paved street time, only what it takes me to get to the trails.

This is using a #25 chain drive. I was thinking maybe I could upgrade to 219 on the first reduction as it seems to be holding up better on the secondary.

Anyone else?

 

[Jeremy Harris]

Lovely pictures, that's a smooth flange, not a sprocket.................

I suspect that the cause was a soft steel sprocket. I bought a couple of #25 sprockets last week and the steel they're made of is like toffee, very soft. While this is OK on a big (30 to 80 tooth) sprocket, small drive sprockets really need hardened teeth.

One way to cure the problem on the new sprocket (assuming you can't buy a hardened one) might be to case harden a soft steel one. All you need is a blowtorch and some sugar, provided that the steel the sprocket is made of will case harden OK. The process is simple, just heat the sprocket to bright red heat and drop into a bowl of sugar. You may need to repeat this two or three times to get a decent thickness of case hardening, but it should make the sprocket stand up to hard wear a lot better. The downside is that the chain will wear faster...........

Jeremy

 

[spinningmagnets]

Great idea Jeremy, I hadn't heard of using sugar before...I had read about ancient sword-makers heating with a bellows-blown furnace, and using finely ground charcoal dust and quenching with hot oil.

Some random links I googled...

http://en.wikipedia.org/wiki/Case_hardening

http://www.ehow.com/how_4558811_case-harden-steel.html

http://www.thehighroad.org/archive/index.php/t-315807.html

 

[dontsendbubbamail]

I am a bit surprised that this would happen. How about a pic of your bike to refresh my memory. How many miles did it take to round off the #25 gear?

Bubba

 

[REdiculous]

The downside is that the chain will wear faster.

Will the sprocket be slightly thicker or is it that the sprocket is then harder than the chain? Other? Just curious.

 

[Toorbough ULL-Zeveigh]

are there any plating shops on-line or elsewhere that do Ti nitride coatings?

 

[liveforphysics]

The downside is that the chain will wear faster.

Will the sprocket be slightly thicker or is it that the sprocket is then harder than the chain? Other? Just curious.

When two surfaces contact, the harder one generally wears the softer one down.

I'd never heard of using sugar before, but it does seem like a perfectly suitable and easy to use carbon source. Should smell a little better than an oil quench as well.

 

[Jeremy Harris]

Great idea Jeremy, I hadn't heard of using sugar before...I had read about ancient sword-makers heating with a bellows-blown furnace, and using finely ground charcoal dust and quenching with hot oil.

Some random links I googled...

http://en.wikipedia.org/wiki/Case_hardening

http://www.ehow.com/how_4558811_case-harden-steel.html

http://www.thehighroad.org/archive/index.php/t-315807.html

Sugar doesn't give a very thick hardened skin and isn't as good as using commercial available case hardening powders (Casenit etc) but is cheap and readily available. For small, thin parts two or three goes with sugar, followed by a quench into cold water from red heat, will give a case hardened skin a few thou thick. This should prolong the life of a soft steel sprocket a fair bit, although once the case hardened skin wears through the wear rate for the rest of the sprocket will be the same as before.

The way sugar works is similar to the way the commercial powders work, albeit with less effectiveness. Sugar is rich in carbon, so dipping a red hot bit of steel into it creates a high carbon solution on the surface of the steel. The net result is that a tiny amount of this carbon gets absorbed into the surface of the steel, raising it's carbon content. Effectively the process turns a thin skin of the sprocket from low carbon mild steel into high carbon steel, similar to tool steel in some ways. High carbon steels can be hardened by heating to red heat and quenching, so doing this at the end of the process hardens the high carbon steel skin.

Jeremy

 

[amberwolf]

Would dipping it in graphite powder be as effective, or less, or more?

 

[drewjet]

Here are a few pics of bike