I'm working on overhauling a 1984 Trek 620. After cleaning/repacking adjustable BB, installing a new 7-speed freewheel, new derallieur, shifters, etc. Everything is back together but when pedaling under any kind of load, I hear "crunching" from somewhere. Can't hear it under light load (like using the granny hi gears) or on the bike stand.
1) BB-- I initially replaced the two caged bearings with loose ball bearings (9 each side). I put it all together and heard the crunching. But then I read that I should have used 11 bearings on each side, so I took it all apart again and re-did it with 11 loose bearings. The adjustment cup is pretty tight so that there is no knocking/play yet is smooth when turning it on the stand. On the other hand, this is my first attempt at rebuilding/repacking an adjustable BB.
2) 7-speed freewheel. Bike originally had a 5-speed freewheel on this 126mm rear. The freewheel went on no problem with plenty of axle space, but to get enough chain clearance for the bottom cog, I ended up removing a spacer. It seems ok, but I haven't yet tried reverting to the 5-speed freewheel. Nonetheless, I hear crunching on any of bottom 3-4 cogs.
3) 8-speed Ultegra bar-ends with 7-speed freewheel (with alternate derailleur routing). I eliminated this suspect by just using friction-mode shifting for now. Still crunchy. I'm hoping that once I solve the crunchy noise, that this combo might just shift ok even though the spacing isn't exact.
4) KMC Z50 6-7-speed chain on a new Tiagra 9-speed derailleur. I tried the old Shimano 600 derailleur. Still crunchy. With 7-speed freewheel and 7-speed chain, seems like there shouldn't be a problem here even though it looks like there is very little space between the chain and the rear adjacent cogs.
Tomorrow I guess I'll try the original freewheel and if I still hear the crunches, I guess I'll either go back to the caged BB bearings or go for a new cartridge BB.
Anything else I'm missing?