Chain Slips/Jerks Occasionally When Pedalling in Top Gear

[woodbine]

I have a 25 year old 18 speed MTB. It has original 6 cog Uniglide cassette and Deore derailleur. The 3 crank gears are original oval Biopace and shifters are Deore SIS. The bike was in storage for the last 20 years and I have re-commissioned it and started to ride it again. The old chain was very stretched and I have replaced it with a new KMC chain and also a new Uniglide hub. This is the chain I bought-

http://www.chainreactioncycles.com/kmc-x8-93-8-speed-chain/rp-prod25424


When I am pedalling in top/18th gear (ie. using both the outer cogs), occasionally the pedals slip forward slightly as if the chain has slipped on a couple (approx.) of teeth. This is accompanied with a clunk, then all is normal for a while and then it happens again. It's a bit disconcerting to be pedalling hard in top and all the sudden the pedals give slightly before retuning to normal.

I'm wondering if it's down to adjustment somewhere or some wear? I'm not sure if this would also happen still using the outer/smallest rear cog and one of the other two crank cogs - as I rarely use the 2 smaller crank cogs. Any advice would be much appreciated.

 

[howard2107]

Check your bottom crank and the pedals, is everything tight, no signs of wear. It sounds like there is wear on the crank allowing the pedal to slip a bit. I may be wrong but its worth a check, and the symptoms suggest this could e the problem.

 

[Globalti]

Typical symptoms of a new chain that doesn't match worn cogs and is jumping, I'm afraid. You need a new cassette and chainrings, or at least the ring on which the chain skips.

 

[lpretro1]

Either worn chainrings or worn freehub

 

[woodbine]

Thanks for your reply howard. I forgot to mention that the part that passes through the bottom bracket that the predal cranks rotate (not sure of it's name) was also replaced. It feels more like a gear slip problem than pedals or crank - especially as it only happens in top gear.

 

[raleighnut]

Is it a tight link in the chain.

 

[steve50]

Will be cassette and possibly chain rings that need replacing. 18 years old , all components will have worn evenly together so they will all need renewing.

 

[woodbine]

Thanks for all your replies. Wear in the cassette smallest cog makes most sense as it's only happening in this gear. Logically, the 18th gear gets a lot of use.

Am I right in thinking that I can turn the cogs over on a Uniglide rather than replacing which may be difficult due to lack of spares?

 

[screenman]

You could stop using that gear and pedal faster.

 

[steve50]

Am I right in thinking that I can turn the cogs over on a Uniglide rather than replacing which may be difficult due to lack of spares?

not sure about turning the gears, never heard of that before, ebay has some offerings http://www.ebay.co.uk/sch/i.html?_o....TRS0&_nkw=uniglide+6+speed+cassette&_sacat=0

 

[fossyant]

Like most, you'll be using that gear too much. You need to find another uniglide bottom sprosket as that one is the locking sprocket. Ebay. Any lower end 8 speed cassette can be split into sprockets, but you'll need a dremmel to take out part of the larger slot on the sprocket - uniglide doesn't have one larger slot.

You really shouldn't be able to wear out a bottom sprocket - you aren't pedalling efficiently.

 

[andrew_s]

Is it a tight link in the chain.

That's what it sounds like to me.
If it was a worn sprocket you would get slip just about every pedal stroke, at least while pushing hard.
A stiff link will only slip when the link feeding onto the sprocket coincides with a harder push - i.e. cranks near to level.
It happens in the small sprocket because that only has about 5 teeth engaged with the chain, so if the stiff link makes the chain ride on top of the teeth, there's less to stop slip.

turn the cranks backwards and look for a kink in the chain as it comes off the lower jockey wheel.

 

[Globalti]

To the OP: your chain hasn't stretched, it has worn.

And you confuse us by talking about crank gears and cogs; they are not cogs, they are rings.