Bicycle Mechanics - Clunking in drive train after 10 miles

I've been suffering from a chronic problem of drive train clunking. It doesn't start until I've gone for 10-15 miles, and it gets worse the longer I go.

Symptom is a thunk sound and I can feel it through my feet as a slight catch. It doesn't happen at the same point in the cranking--my impression is that it is coming from the back somewhere. It is worse when going up hill or fast, and gets worse the longer my trip lasts.

The chainrings were badly worn, and factory standard were too big for effective spinning, so I just had the LBS shrink all 3 of them. The chain was stretched and I thought it might have a kink in it, because lube seemed to help the clunking, so they replaced the chain for me also.

Just brought the bike home tonight and the new gear is an improvement, but doesn't seem to have cured the thunk/catch.

Bike is 16 years old, with Suntour 4050 shifters. 3 gears in the front and 6 in the back.

I wonder whether your freewheel ratchet pawls are wearing out or sticking; either way, this is potentially dangerous. I suppose as well that the grease in your rear hub or bottom bracket is breaking down as it warms up; how long has it been since these were repacked?

I had the same problem and was shocked to find out it was a loose kickstand hitting the crank arm.

I can't imagine how it would get worse after 10/15 miles, unless your pedalling changed as time went on. If your rings were worn, and you replaced them and the chain, the freewheel gears are probably worn. Even if it's not the problem, it will accelerate wear on the chain, and the chain will probably jump on hard acceleration.

Otherwise... I suspect the BB. I'd suggest taking it apart and overhauling it, inspect the cups carefully, checking for cracks. How does the spindle look? Clean, replace the bearings, and repack with grease.

Hubs are sealed, but I don't think it could be them because I feel it through the pedals.

The ratchet pawl isn't something I want to hear about, but I guess I better look into it.

The Bottom Bracket hasn't ever been taken apart. I'm thinking this is something I should do myself. What with putting updated levers on it this week, smaller chainwheels and a new chain, I'm getting closer to the cost of a new bike. Just as long as little ball bearings don't go rolling all over the floor (I'm assuming my bike is pre-cartridge technology). However, the pedals are directly connected to the pedals, so I wouldn't expect that kind of 'catch' that I can feel through the pedals to be related to a BB problem.

Is it possible to get new freewheel parts? The LBS doesn't seem thrilled with mucking about with that older stuff. If its a prob with the pawl, am I just looking at taking it apart and ensuring that it is not corroded, and is well-greased, or is it fatal?

If it is the end of the rear end, I think my best bet would be to throw out the hub and upgrade to a modern cassette, with this possibly being the opportunity to upgrade to more than 6 gears. (I spent an hour on the Harris site last night looking at pictures of people stretching chainstays with 2x4s).

I had a short discussion about upgrading my bike on the Touring section, but thought this group might be better for the mechanical question of the clunking. But I'll toss the question out here: I've got an original Bianchi Volpe from the late 80s. Japanese lugged frame, Suntour 4050 derailleurs, canti brakes, full braze-ons, barcon shifters, 36-spoke wheels. I like the look of a lugged steel bike and I like the way it feels. Although I am considering upgrading to a custom tourer, I wouldn't mind upgrading this one a bit more. Any reason not to think that this 'classic' frame from the late 80s isn't worth updating with a new derailleur?

Or should I throw it away and start from scratch with a Mercian or Waterford with nicer components?

Thanks,

Jay