austinbikebill

Hi all.

First, a thank you to everyone on this forum who weighed in on my shifter upgrade from downtube shifters. After considering an upgrade to index shifters, I ended up staying "analog" and going with some dia compe bar end shifters instead. Very happy with them.

On to my current problem.

I have a drivetrain that is effectively a 9 speed at the moment. If I try to go to the large chainring - largest sprocket combination, the chain comes up short, maxing out the derailleur and locking up the chain so tight that I have to take the wheel off to release the tension and reset the drivetrain.

I think I still have the original chain on the bike, so I bought first a 7.3mm 1/2" x 3/32" 116 link chain designated for 5-8 speeds and installed it.

At the 116 link length, the new chain would let me get on to the large chainring - largest sprocket combination, but the chain would then skip-jump when on the two smallest sprockets,

I took out first 2 links (to 114 net links), then 4 links (to 112 links) and the same behavior worked on larger three sprockets, skipped on the smallest two sprockets. Oddly, at 112 links, it would still go onto the large chainring - largest sprocket combination.

I then bought a beefier 7.8mm 116 link chain designated for 5-6 speed use, and I got the same results: skipping-jumping on the lower 2 sprockets, good on the three largest sprockets.

I (think I correctly) measured the legacy chain the with a caliper and came up with 7.96-8.0mm width (at the pin: I got 7.28-7.30 at the pin on the first chain and 7-76-7.80 on the second chain).

I no longer have the original Suntour "Blue" series derailleur, having replaced it with another Suntour derailleur with the same jockey arm (?) length.

So what do you folks think?

Is my drivetrain so old that I need an even beefier single speed chain?

Is my derailleur just tired (it probably has over 10,000 miles on it since installed) and not maintaining sufficient tension in the chain when at its most slack on the smaller sprockets.

I would really like to get over the hump on this 9 speed issue and have my Nishiki fully functioning again, so any insights/ideas would be most appreciated.