Don't worry, BCD is the diameter the bolts that hold the chainrings on. Your crank is a 130mm BCD for the big and middle chainring and 74mm for the small chainring. Most road triples are standardized on these dimensions.

Square taper is the interface between the crank arm and the housed axle that is held on the bike frame. This housed axle is called a Bottom Bracket, or BB for short.

TA .. manufacturer of chain rings and cranksets, french.
square taper ,the meeting of traditional BB axles.

Shimano's indexing stuff is trademarked as STI

traditional friction shifting by hand shifted past the cog slightly
and then you pulled the lever back a little , to center the shift mech over the cog.

the index stuff got pickup ramps , pins and shortened teeth,
so the mech only goes from over one cog to another .

relies on the careful adjustment and alignment of the drive train as the segmented detents .. klicks,
on the lever and the pre determined motion of the derailleur sideways have to be just so..
and need synchronizing.
front lever and rear the shifter .

All of these statements are true but probably indecipherable to the OP and to many others reading this.

so very true, I feel like I need to learn a second language here with all the accronyms, trade specific jargon, and slang.

A lot of us fudge on this stuff. For example if you do the smaller granny switch and the chain won't pick up cleanly to the middle ring the typical solution is to click the shifter to the middle position plus a little and hold that bit of extra travel for a moment until the chain picks up on the middle ring and then let go. It's a touch of bother but it works just fine.

Aha, A Phil Liggett fan!

OK, I am guessing these are items I can find on the net, and are designed to keep the chain from dropping off the granny gear to the inside. Is that all correct?

Yes. Be careful to select one to fit your seat tube. They fit using a clamp, so the chain guide needs to have the clamp diameter shaped to fit the diameter of your seat tube.

https://www.treefortbikes.com/product...-Dog-Fang.html

You will see in the drop down box, that the item is sold in three sizes, pick the size that matches the O.D. of the seat tube.

OK, did a quick search on the net and found all three. I like the looks of the N-gear best and imagine that I have sufficient materials in my shop to just fabricate one with 14ga. stainless steel and the appropriate sized hose clamp.

thanks for all the help y'all
klc

edit: after looking at pricing; it probably wouldn't be worth my time to make any of them though. I can get the N-gear for $12.00 shipping included direct from the manufacturer. Just need to measure the seat post now.

I can't recall who makes it right now but there is a "chain watcher" that sandwiches between the bottom bracket shell and the driveside bb cup and has a projection that sticks up to retain the chain. It can be used on frames with odd shaped seat tubes where a circular clamp won't fit.

I just E-mailed Nick at N-gear (https://www.gvtc.com/~ngear/orders.html) with the measurement of my seat post and a concern about how close the shifter cable is to the post. I'll let you know how it turns out.

I had to look up who you were reffering to...

I dad was Scottish and I guess I picked up phrases and usages from him. Depite being born here someone asked me how long I'd been in Canada when I was around 17.

I'm sure Phill is a great guy but in my case I just talk like that... Part of what often seems like my own solitary battle to keep the English language interesting

OK, now that I have been doing some research online and taking in all the advice here, I have other questions. Keeping in mind a meagar budget, where would be the best place to buy a 28T or 27T inner chainring? How can I be confident that it will bolt up to my middle ring without problems.

I'm also thinking a few calls to the local shops might turn up a fair enough price on the swap so that I don't have to worry about the labor and making mistakes in the process.

https://www.loosescrews.com/index.cgi...d=269488020997

OK, since that link did not mention anything about compatibility with one or the other bicycle or crankset, is it safe to assume most of the modern cranksets have universal bolt patterns?

Generally yes. You have to get a chainring with the correct number of bolts (duh) and the correct BCD: https://www.sheldonbrown.com/gloss_bo-z.html#bcd

now; that is a useful link. tons of information. I even now know for sure what BCD is; something I was unable to decipher earlier ( or maybe just did't see and comprehend at the time).

thank you.

Bookmark the Sheldon Brown link. In fact, go through the whole site. I've been playing with bicycles for over 30 years and I still find interesting information there.

yeppers created that bookmark as soon as I saw what was there.

The OPs bike is Shimano equipped which uses the large-large system. AFAIK only Campy uses the small-small system.

I guess you have determined that you need a 74 BCD for you small chainring. Your local bike shop can get these for you for $20, about what you pay online unless you watch ebay. I did not have good results using a Sugino 26T ring on a Shimano triple. I had better results with a Salsa ring. I read somewhere that Sugino uses a slightly different spacing. It worked fine with friction shifting but not with indexed which is what you have.

We're experiencing single digit low temps right now and my shop is not heated, so I have yet to measure anything. Hope to get to that before the weekend though.

Just a quick update on a couple things. I visited with one of the wrenches at a local bike shop today who said he would sell me a 28T granny ring for $20 and a 12-26 rear cassette for $30 since I had indicated I also wanted new tires & tubes and a basic tune-up package ($40). Can''t beat a deal like that; heck paying shipping would have the cost of the granny well over what he is going to charge. I'm taking them the bike Friday afternoon.

I also requested the N-Gear Jump Stop on Sunday morning and the guy had it to me in today's mail. It's an amazingly simple and beautifully effective device; well worth the $12 price tag.

Appreciate all the advice here.

Another update: I got the bike back from the shop on Monday but weather kept me from riding until today. Even then, I only got to cruise around the block a couple of times as I spent the better part of my "ride time" working with the grand kids and their cycling needs. Just wanted to say thanks again for all the input. The new gearing definitely makes hill climbing easier, but seems it is a little difficult to shift up from the granny ring to the middle. I occasionally had to bump the shifter slightly a second time to make the jump. I'll figure it out as soon as I can get a longer road ride in though.

And the N-gear jump-stop; great product!!!!

FINALLY!! I got a chance to log some miles on my typical southward route from town. I rode out 6.15 miles encountering three hills out and three back and the new gearing ( -2 on the granny ring and +1 on the rear) made a huge difference on the ease of climbing these hills. I'm very happy with the results.

thanks y'all