Hi,

I've recently changed my chain on my mountain-bike because it was all rusty and I was unable to get it cleaned. Now the following issue has come to light : when riding my chain 'skips' on the 5th and 6th cog of my 7speed freewheel. The chain only skips when riding the biking, when I turn it upside down and engage the drivetrain by spinning the cranks the chain does not slip. The chain only skips on the 5th and 6th cog, not on any of the other cogs.

Does this indicate that the 5th and 6th cog of my freewheel are worn out?
If so, I need to replace those cogs but I guess you can't replace individual cogs so I'd have to buy a new freewheel altogether, correct?
What model should I get? The freewheel I have now is exactly the same as the one described in this thread: Sunrace HG II. It has the following cogs: 13T-15T-17T-19T-21T-24H-28H(7speed).
Would this Shimano freewheel fit : http://www.amazon.co.uk/Shimano-Tour.../dp/B003662HBK ?
For removing my freewheel I would also need a freewheel remover like the Park FR-1, correct?

Regards,
logion