Let's assume that I installed a brand new bottom bracket with a spindle that either too short or too long. Once the chain rings are properly alined (a proper chain line is achieved), with the shortness or longness show up on the left side of the bottom bracket's receptacle once the left crank arm is installed??

The devil is in the details. Right side spindle length is more critical because it affects the more critical chainring/chainstay clearance, and chainline. Left side clearance is rarely an issue, so it's mostly about Q-factor and Right/left crank symmetry (not a real issue within limits, but some get worked up over that).

With a cup/cone bottom bracket, the spindle position is predetermined by the right cup, which sits tight to the frame. However, you can sometimes adjust chainline by reversing an asymmetrical spindle. Some cartridge bottom brackets allow you to float the spindle right or left a few millimeters allowing you to fine tune chainline. Obviously the left arm moves in or out the same distance.

All in all, if the chainline is OK, I'd say you're probably OK all around and don't have to sweat details any farther.

My L crank brushes against the L chainstay. My R crank arm is about 1/4 inch further away from the R chain stay. 8(

Need more info. If it's a cartridge BB can you float it to the left? Or if the spindle is asymmetrical, can you reverse it to advantage. Otherwise you need a spindle that's longer on the left and maybe shorter on the right.

BTW- next time save time and get the right answers faster, by stating the problem right off, and provide the specific details so people can give you an informed answer.

Don't you remember-
https://www.bikeforums.net/bicycle-me...m-bracket.html

What kind of bike? How wide is the frame's bottom bracket shell? 1/4 inch difference sounds to me like a 68 mm bottom bracket in a 73 mm BB shell.

A-Ha! That thread mentions and old straight Sugino crank arm on the left. That won't generally work on 1990s MTBs.

Are you still trying to set it up with a straight Sugino crank arm on the left? They generally only fit frames with 126 spacing, maybe some 130mm spacing with a long rear triangle that allows tight chainstays for a while before spreading out to the dropouts.

You need a left crank arm with an offset to work on your 1993 bike with fairly short stays and 135mm dropout spacing.

Okay, it sounds as if I need an "exact" replacement, a Shimano having the same model number. As a gamble, I purchased a Shimano (different model number) and it's as straight as the Sugino arm. So this might be an issue with the offset of the substitute L crank arm and not the BB.

And looking at a recent ebay auction, the original crankarm, a Shimano, is, indeed, curved and therefore has an offset different from replacement straight crank arm.

Left arms from cranksets that take really long BBs, like 122+mm, might have straight left crankarms also, I reckon.

So maybe look for left crank arms from cranksets that require 110-117mm bottom brackets.

ALRIGHT!!!!! It's finally sunken into my thique skull. BB length??? Spindle length??? Let the LBS decide and I'll replace the whole drivetrain with a new crankset, chain and either a new cassette or freewheel.