pulley wear; is this a record?

[Brucey]

From the LBS scrap bin; a Shimano 'Sport LX' mech, from circa 1988, (back when shimano knew how to design a rear mech which didn't do a 'death plunge' into the spokes as soon as it touched them..... ). "Wasn't changing gear properly", apparently....

"vestigial" is the word that springs to mind....

With good pulley for scale. Photos of a good mech herehttp://velobase.com/ViewComponent.aspx?ID=3aea92ae-601f-4a30-807f-528ebc8484d1

I've seen quite a few rear mechs in states of distress, including 'broken pulleys' and 'no pulleys' but I don't think I've seen one where the pulleys were simply worn this small....

The other weird thing is that the rest of the RD is OK, and once decrudulated, may ride again....

seen anything like it?

cheers

[Bonefishblues]

It's a fossil, shirley? You must have dug that up, not take it off a bike!

[robc02]

seen anything like it?

Yes! Back in the 1970s a clubmate showed a group of us (he might have been trying to sell it to one of us, actually ) a Campag Record mech with jockey wheels practically worn away. He was ridiculed by some, but, as a teenager new to cycling, I was quietly impressed that he had done enough miles to have that effect.

[iandriver]

What would be interesting would be to know how much the crud affected the shifting. I can't help wondering if the crud actually made it better when that worn.

[mig]

what was the weight saving?

[Tigerbiten]

I've done that to the jockey wheels on my recumbent trikes Rohloff chain tensioner a couple of times now.

If the chain is always coming in at an angle to the lower jockey wheel because you stay in top gear, you tend to wear the tops off the teeth.
It's the same with the upper jockey wheel if it's slightly offset from the sprockets and/or bent.
It took me around 2 years and 15k mile to wear the lower one to that state the first time due to the chainline under the seat.
Since then I treat them as wearable parts.

YMMV .........

[Brucey]

FWIW a fairly unworn 10T pulley has major/minor diameters of 38.4mm/32.4mm. The worn pulleys measure 29.5mm/26.9mm. Quite a lot of material missing....

IME the most rapid initial wear occurs when the pulley bushing doesn't turn freely and/or the chain is badly worn; both these conditions encourage there to be load and /or movement between the chain and the pulley teeth. If the chain runs onto the pulley at an angle, the teeth can wear on the sides and this may limit the life of the pulley. Some recumbents use a guide pulley in tension run of the chain; these see load all the time and can wear horribly. If a RD is used when it is badly adjusted, you can get side loads on the teeth all the time and the guide (upper) pulley can wear out much faster than normal.

In this case I suspect that the chain was worn and this started the ball rolling; the reason I say this is that there are still detectable signs of ten teeth on each pulley. By contrast if the pulley bushings are super-draggy the teeth get knocked off and don't persist; you end up with a small round thing instead.

There are two complications to all this; the first is that the worst wear also occurs with riders that pedal at a glacial pace and/or on small chainrings, i.e. at a very low chain speed. By contrast at higher chain speeds, the centrifugal force arising from the chain changing direction effectively means the chain is pulled less tightly against the pulley. This determines the minimum chain tension that you can have from the derailleur spring; if it low enough and the chain speed is high enough the chain leaves the pulley on tight turns. This may be part of the reason that many RDs have a tab behind the lower pulley; the chain can obviously come off when it is completely slack (wheel out) but there are other conditions that may cause this too.

The second complication is that once a pulley is worn, it is usually going to wear faster and faster. The reason this occurs is that once the diameter of the pulley is reduced, the pitch of the valleys no longer matches the chain pitch, and under a wide range of conditions the chain rollers slide against the tooth faces on the pulley, causing ever more wear. The same thing happens when a super-worn chain is used with good pulleys, but in this instance it is probably the least of your worries....

cheers

[Greystoke]

I'd say that the owner of that bike got their moneys worth out of that component

[Samuel D]

Was there anything left of the bushings on which the pulleys spin?

[Brucey]

Was there anything left of the bushings on which the pulleys spin?

oddly enough, yes there was. They were worn but not that badly; they weren't free running but they still turned well enough that the pulleys weren't rounded off entirely. This mech used a standard (metal on plastic bushing) lower pulley and a metal-on-metal bushed 'centreon' guide pulley.

cheers

[andrew_s]

Not only had the pulley lost its bearing and been reduced to a narrow ring, it had worn half way through the bolt holding it in

[Brucey]

and this is despite some 'maintenance'; in the photo above the inner cage plate is on upside down....

cheers

[andrew_s]

I hadn't noticed that - I'd just assumed it was lumps of crud.

The rider concerned was well known for extracting maximum life from his bike parts, though he does seem to have become more amenable to spending money the last few years.
Repute has it that the frame has done well over 300,000 miles.

[mattsccm]

That's not worn, there are bumps.
As a youth I used to use other peoples worn out ones and used them until the chain slid sideways. As near as damn it circular.

[Brucey]

BITD some RDs came with circular pulleys, i.e. ones with no detectable teeth at all. Some old campag mechs had (steel) pulleys with many small bumps on them;



presumably so that even if the pulley bearing started to get a bit draggy, the pulley would turn for longer before the chain would slide round on the pulley surface.

My theory is that these RDs don't shift very well if you use modern chains in them; I think that older (fully bushed) chains usually had deeper side plates and this would give some lateral traction even with a (nearly) round pulley. The closest I can find to this kind of chain now is something like this wippermann model



Hopefully it isn't just my imagination that I can see the inner side plates standing proud of the rollers. Obviously you can't use the split link in the picture with a derailleur, either.

By contrast modern RDs often have extended teeth on the guide pulley;



which gives pretty good lateral traction with any chain.

cheers