Chain skip options on vintage 'frankenbike'

Question

I have a late 80s Bianchi Volpe which came with Sakae Ringyo SX cranks and bb, SunTour barcon shifters and derailers, and SunTour chain.

The freewheel was aftermarket 7 speed and never rolled well so I replaced it with a Shimano 7 speed available at my LBS.

Everything was working well and the drive train was low noise and decently shifting despite the frankenbike nature and problems others have had, specifically that SunTour shifter throw and cage travel is not SIS compatible.

Recently I replaced the chain with a SRAM 9 speed based on reports that the narrower chain is even better on noise and can confirm, drivetrain is much quieter.

But now the chain skips under load. I know cog wear can be the source of this skip, but neither the chainwheels nor freewheel appear to have that high wear, and the original chain was only a few hundred miles past the Park Tool's ".75" indicator mark.

Attached is a picture of the filthy cranks (Chicago winter salt and sand included).

If I do need to replace the two largest chain wheels, must they be SR? Other brands seem more widely available, assuming BCD matches.

Edit: Picture for real this time. Dirty freewheel:

Answer 1

First, I'd trouble shoot why the chain is skipping. Does it only happen under heavy load? Does it always happen in the same place (maybe a stiff link)? Does the derailleur do something funny?

If the BCD and bolt pattern matches, stick whatever chainrings you want in there (subject to front derailleur constraints on chainring size + tooth gap). As for if your chainrings are worn or not, the picture isn't there, but there are plenty of other questions (see sidebar or search) on this SE to check if your chainrings or cogs are worn beyond.

While using a 9 speed chain on a 7 speed cassette should work, it will likely be a bit sloppier than using a 7 speed or 8 speed chain (they are narrower than the chains that the 7 speed cogs were designed for). They're also pricier. So, I'd also go back to a 7/8 speed chain in the future.

The change from Suntour freewheel to Shimano freewheel shouldn't really have caused any problems other than maybe some minor adjustments (unless you're running a microdrive drivetrain).

Answer 2

So a few days after posting this, my guide pulley flew off. I lost the pulley, the plates, and the bolt and bushing amid road debris and lack of time for a thorough search.

After installing a new pulley, bolt, and bushing I adjusted limits and the barrel adjuster tension, and everything has behaved perfectly. I probably should have checked these earlier, to see if mal-adjustment was the source of my issue. Possibly something was wrong with the guide pulley that a quick visual glance did not reveal.

Another hypothesis is losing the pulley under load and catching the chain on the cage, bent the derailleur ever so slightly out of adjustment.

To everyone who believes that a wider chain the solution, that's okay, I just assume you haven't had direct experience matching Suntour Accushift to Shimano freewheels. A nine speed chain works and it works well, far better than a 6/7/8 speed chain does when it comes to dealing with Accushift's tendency to "overshift."