Fahrenheit531 

As the subject line says; looking to go slightly smaller on the big ring. Japanese only for the bike in question, so Sugino/Shimano preferred. 50 or 48T. Thanks much!

EDIT: Chainring found.

ThermionicScott 

You're probably looking for something along the lines of plain C&V style chainrings, but I used a modern ramped-and-pinned 50T Shimano ring a few years ago and was pleased at the shifting. The 4503 model seems to be gone, but you can still get:
5703: https://www.amazon.com/SHIMANO-FC-57...00553OYFE?th=1
3503: https://www.amazon.com/Shimano-130mm.../dp/B00N6KHI56

I have a couple of lightly-used plain Sugino 48T and 50T rings, but checking back, I paid $30-40 for those, so I'm not sure if I'm ready to let them go for much less than that, yet.

delbiker1 

I see you prefer a Sugino or Shimano, but a new 130 BCD 48T Vuelta is available on Ebay. I have a 48T and it works with Shimano 6500 great. I believe Jenson USA 50T Sugino in 130 BCD but no ramps and pins. I also have one of these on a bike and it shifts well, not great. The Sugino is steel and heavy, the Vuelta is aluminum and light.

https://www.ebay.com/itm/VUELTA-8688....c100752.m1982

thinktubes 

Be aware that the 5703 is for a triple and has several mm of offset, which will affect your chainline.

ThermionicScott 

I'd noticed it flared out a bit, and the "03" was a giveaway that it was for a triple, but I never bothered to measure the chainring spacing. It worked fine once I'd set up my FD for it. Friction front shifting, of course.

canklecat

Ditto, Vuelta, if you don't mind going outside the traditional Japanese brand names. I have a Vuelta SE Plus ramped and pinned 50T big ring on my '89 Ironman and it shifts much better than the original Suntour. And I've swapped between Vuelta plain 38T and 39T small rings, to suit my 13-25 or 13-28 freewheels for the expected terrain on long rides.

Outstanding values. I think I paid $7 for the SE Plus via Amazon warehouse deals because it was described as "damaged packaging." The chainring was in the original plastic bag with folded cardboard hanging tab, so there was nothing to be damaged. The others were $12 and $15.

Fahrenheit531 

Thanks all for the suggestions. Took a look at the Vuelta but they're just not doing it for me aesthetically, at least not for this bike; I'll file the name in long-term memory for future reference though. Looks like I have a line on a lightly-used Sugino, so victory may be within reach.

Fahrenheit531 

Chainring found.

canklecat

Yeah, the Vueltas are functional and excellent quality but generic looking. I rarely pay much attention to the aesthetics of cranks and chainrings, but coincidentally yesterday I was gifted a parts bike with a really good looking Ultegra set and I gotta say... I like it. Darned spiffy and streamlined.

And I've always liked the streamlined appearance of the Suntour GPX group on my Ironman, including the cranks, but the chainrings themselves were nothing special. The Vueltas look pretty much the same, but a very slightly different shade of gray -- less blue than the Suntour.

The more relaxed B-group of the roadie club I ride with has recently begun encouraging folks to show up with their classic steel bikes, and I'm developing an appreciation for the subtleties of good classic design now that I'm seeing more 1970s-'80s steel bikes in person. For one thing I'm unexpectedly enamored of those narrow 38cm handlebars -- which, coincidentally, would fit me well since I'm pretty thin. I've tried drop bars up to 44 wide and felt splayed out like an albatross -- not necessarily a bad thing since I have albatross bars on my casual cruising hybrid.

Anyway, I ramble. But I can see why you'd prefer a certain aesthetic for every component in a project bike.