Having problem to make a weird setup working (3×3)

I need some help and opinions with a weird build I’m trying to make.

I’ve ripped apart cogs from two cassettes (one brand new) in a week, so I went back to my backup drivetrain I’ve kept in a parts bin – 3×1 Tringlespeed I used to ride happily in 2022-23 years.

It’s a fun build, but it has it’s limitations – range, but it's also pretty worn by now, so while I was riding it two years ago I’ve purchased FireEye 18t, 16t and 14t SS cogs in order to adjust my range for a future replacement, so I thought: why not put them all on the bike and have all the possibilities at once? Easy on paper, a quick 20 minutes adventure, what wrong can happen, eh?

Testing out the layout of cogs

 And that’s where problems started.

Parts in th work: Neco 22/32/44t triple chainrings at front, KMC Z7 7sp chain, 18,16,14t SS FireEye cogs – all 2.25-2.3mm thick, 7-8sp chain compatible, according to manufacturer. Shimano TY300 RD, TY500FD. Everything is brand new, except FD,RD.

I assembled it all together and when I was testing it out on a stand, everything worked great. But once I’ve went for a test ride it was not working at all. Chain skips on all of rear cogs like mad (video) even at light pedaling. Chains seems to grab onto teeth of cog and go over it.  RD is positioned directly over the cog, so its not an alignment issue. 

My first conclusion was that chain inner link’s and cog’s width tolerances are too small and tooth drags the chain off – chain inner link width is 2.45mm. Cogs are 2.25-2.3mm. it was sitting pretty tight.

What really puzzles me, is that my current 3×1 setup (which essentially is the same) works flawlessly no matter how hard I push! I measured parts on it and it has 2.25 cog, but chain is a counterfeit KMC X8 with inner width of 2.9mm. That reassured my idea of tolerances being the problem, so I’ve given cogs to a turner at work to shave off 0.3mm of the work area of the cog.

Machining done. Edges after machining are filed down manually

But the result was the same, so now I’m confused what to do next. A little detail that might be important: when it is in biggest cog and biggest chainring, the RD is stretched the most (giving more chain tension) and it can withhold more load before it starts slipping and vice versa, in small-small combo it is slipping at much lighter load.

My ideas of possible solutons would probably be:

1.       Try another 6sp chain with a bit more width (My old z6 chain is measuring 2.6-2.7 width)

2.       Try using a SS chain (but I have serious doubts it will have enough flex to work in such scenario)

3.       Using intact cogs from the remains of a new cassette I have after one cog was blown up and finally achieve that weird goal of having a 3×3 drivetrain.

4.       Give up on the 3×3 idea and just get an 8sp cassette with a “traditional” 1×8 setup.

Please share your thoughts?

P.S. The more I look into the abyss, the more it looks into me old and new parts, I think I notice the cog profile is a little different on old setup, maybe. Maybe with a traditional SS use FireEye cogs work ok, but with a derailleur as chain tensioner, slack is too much and it pushes chain off too easy?

P.S. 2: Sorry for the long read, but I don't think its possible to explain the problem properly without all the details