Changing chain and sprocket together?

Here's a question for you techy types.

I've been told by several dealers and trustworth mechanics that I should always change my sprockets and chain at the same time. However, after asking further more directed questions I hav never got a satisfactory explanation as to why this is strictly necessary.

I have(again) been very stupid and let the winter salt get to my chain(and everything else) and it's in a pretty bad state. My scottolier doesn't seem to ba able to handle the winter months, altho I don't think I had it turned up to 10.

My question is, why is it necessary to change them together? And is there a tolerance window where by I can change them out of sync. It's not been on for long, 3k at the very most.

Thanks

Nath

(regretting not using the ACF50 I have sat in the shed)

[Sid Squid]

Either the chain or the sprockets being worn places an uneven load on the other - you won't get full life from a new chain if used on worn sprcokets.

What is actually wrong with the chain? I'm assuming rust, but if it's only here and there (usually on the ends of the pins) it will clean off with WD-40. If it is seized with the stuff then it is probably stuffed.

Chain and sprockets wear together, and the surfaces all fit pretty snugly. I recently changed the chain on my pushbike (single speed, no derailleurs), but not the chainring (front sprocket) and it makes a horrible grinding noise, which is slowly disappearing, as the chainring wears to fit the new chain. Passable, considering the power in my legs, on a motorbike, will very quickly wear at our shiny new component, as well as the old ones, and may cause a chain break, which is NOT GOOD.

My SV chain suffers terribly from rust if the bike is under the cover, not being used, but in the places I earlier said.

[Biker Biggles]

Theres something seriously wrong with your scotoiler if the chain is sh&gged after 3000 miles.

[mister c]

We always taught people to change both when doing the CBT. Same reason as Sid really, the used part will wear the new part out a lot faster

Thanks for all your responses. I think I knew this already but had forgotten the specifics.

Rust is all ove the pins and side plates, I don't even think wd40 and an oil bath would rejuvenate it. I think I to pay more attention to adjusting my scotoiler for the winter. This is the 3rd chain i've had to replace since it was new back in 04, although i have done about 30k on it.


Expensive lesson.
Cheers guys.

Nath