Do I need a new crankset

[taximan]

A couple of weeks ago I picked up a load of grass which got caught up in the rear Mech, and completely destroyed it and also knackered the chain. As the chainset was a bit worn I fully expected to replace the whole of the drivechain, however My LBS said that the crankset seemed to be OK and and on his advice I retained it and renewed the chain, freewheel & gears. Over the last few days the chain has been slipping, mainly in 3rd & 4th gear, so am I right in thinking I will now need to fit a new crankset. (the indexing seems OK.)
Another thing I am thinking about is to fit a a lower geared triple to help me cope with the hills around here. (I am not as young as I was and do struggle from time to time) Will my average speed fall dramatically if I do this, most of my riding is on road and in very hilly terrain.

 

[MontyVeda]

what's the rear cassette like?

if it's only slipping in two gears, it suggests it's the back cogs and not the front ones

 

[taximan]

what's the rear cassette like?

if it's only slipping in two gears, it suggests it's the back cogs and not the front ones

Its not a cassette, its a freewheel and it was new about two weeks ago.

 

[MontyVeda]

ah yes, now I've reread your post, it is!

regarding your chain rings, if they look worn, they usually are.... or if you can pull the chain away from the ring as shown below, they're worn.