changing gearing

I've got a slight issue with my old 1980s Bianchi. Its a bit hilly round here to say the least and when I get out of the saddle the darned thing jumps down a gear making life a good deal harder than it needs to be.

Suspecting its a worn chain I had a quick measure using the 12 links theory and its between 1/8 and 1/16" long so it needs changing I reckon.

The old bike runs an Ofmega front chainset and Simplex SX610 rear deraillier, I can't see any markings stating what the (6sp)freewheel is or what the hubs are.

I was thinking I'd just swan into a bike shop and buy a new freewheel and chain but oh no, its not that simple as its 'old' and everything now is 10sp and more.

So...Help! Where do I get a new chain and freewheel? I don't have an issue with changing the number of gears but would like something a tickle lower than the 24tooth biggest at the moment, its friction shift so indexing isn't a problem.

Will

Try a new chain first, most bike shops should have a 7 or 8 speed chain which should work.

If the new chain jumps then the sprockets are also worn. I gather new freewheels are still made but I don't think most bike shops stock them.

these guys will have wht you need ...
http://www.spacycles.co.uk/products.php ... 0s112p2333

Cheers, are all freewheels the same thread, no difference between Shimano and Campag etc?

Will

How about these -

http://www.retrobike.co.uk/forum/viewtopic.php?t=145536

Will, first make sure you haven't got a tight link.
If your worn chain had lived its life with the same freewheel I would not expect it to slip, and surely not on the larger cogs.
If you mean it jumps on to the next smaller cog then first get some tension on the chain, and make sure you change gear far enough.
A worn chain will run on new cogs, but a new chain will not run on worn cogs.

I used to reckon 10 minutes to change a freewheel and chain on any bike, did literally thousands.

Thanks Keith
It does jump to the next gear down, I've adjusted the stops so the chain just jumps spoke side then eased it back a tickle to stop it going spoke side.

I've no idea if the freewheel and chain are original but I suspect they both are, theres virtually no wear on the wheel rims and they are correct for the bike as far as I can find out.

As I said before the chain has stretched a bit going by the 12 link Sheldon Brown theory. I haven't checked for stiff links, I'll do that next.

I do want to change the gearing a tad so I guess changing the freewheel and chain at the same time would be sensible anyway.

Cheers for the advice chaps

Will