Chain stretched after long motorway journey?

[Lord Percy]

Just rode from London to North Yorkshire on Monday. Now yesterday, while doing a 10 mile stint to go see a mate, I heard an odd metal slapping noise a couple of times, so quickly pulled in to find my chain had become ridiculously slack. I presume this was caused by the 220 mile journey I made the day before. But how? Is this normal?! It's my first long run so I don't really know. When I had a new rear tyre fitted a few weeks ago the mechanic did tell me the chain and sprocket needed replacing soon, so yeah it's an old chain, but still I never thought it could be stretched so suddenly like this. Is it even possible? The only other explanation I can think of is that the mechanic didn't refit the rear wheel properly so it just loosened over time.

Thoughts?

I've re-tightened it and have a new chain ready to fit but still I'm curious as to whether this is a normal thing or what.

Cheers

[Sako]

Chains don't actually 'stretch' the holes where the pins are located wear in an 'oval' shape which in turn causes 'lengthening' of the chain, so I can't see this happening over a 200 mile journey. It will have been a gradual process of wear.

[ficedula]

If it's nearing the end of its life, then yes.

The chain on my YBR lasted 16,000 miles; the first 12,000 miles it never needed adjusting between services. Then it started needing adjusting every month ... then very quickly started needing adjustment every week - so probably was about every 200 miles - at which point I replaced it. So your experience isn't unique - but could be a sign that you really should be changing it.
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Bike history: YBR125 -> XJ600

[Lord Percy]

Sure, so it is a reasonably normal thing . I'll be honest... I didn't even remotely check the chain tension before I set off but on the other occasions when I have looked at it, nothing was ever any worse than before. Oh well, chain is dying, I'll stick the new one on soon Tah!

[Sako]

[MatteyA]

[Lord Percy]

[Walloper]

Chain and Sprocket Wear:

The pins will wear the bushes which will affect the pitch of the chain. Pitch is the distance between the centre of the pins.
This in effect will be like putting a chain with a 'too big pitch' on the sprockets.

So when a worn 'too big pitch' chain runs over the sprockets the bushes do not meet the places in the sprocket properly but will grind away anything in their path. Causing hooking and chipping.

This is why you always fit new with new. A worn sprocket may not affect a new chain but the new chain will eat the old sprocket.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[doggone]

I find you can often sensibly fit a second chain without new sprockets but it won't last as long as the first one.
It isn't a recipe for disaster, but if you don't know what a previous owner did/didn't do, it makes sense to do a full swap.