1986 Miyata nine twelve 912 -- upgrades to hub and bottom bracket

nativewisdom said:

I have a 1986 Miyata 912 that I have just replaced handle bars, tape, brakes, rear deraileur, front derailer, cables, housing and added bar-end shifters to replace the downtube shifters.

I am maybe interested in replacing the insides of the bottom bracket, but have no idea what to do in there (although I replaced all the other stuff above on my own through online videos).

I do not even know what size bottom bracket I have. Everything is running smooth so should I not bother?

I am interested in replacing the guts of the hub. Is that possible? It's all a sealed unit, right? But I do not have any idea what to order. Mainly would like to replace rear hub and get a 9s or 10s cassette to replace the 6s.

I do not know how to find out any of the info I need about the bottom bracket size or what I need for the hub guts.

If the bottom bracket is running smooth then why bother? You shouldn't, there's no need. But if you decide to change it out you need to know the manufacture of the bottom bracket. It can only be a Japanese manufacture, and probably Shimano, and probably Shimano Dura Ace 7200 or Shimano 600 because that bike was 2nd from the top of the line Miyata and the top model had Suntour Sprint and the 2nd from the top had Shimano 600ex. Thus the older series of Shimano's were square tapered and probably either model UN91 or UN72, but I'm betting it's the UN91.

Why replace the freewheel with a cassette? More gears don't equal more range just more choices of gears within the same range. You could go with a 7 speed freewheel and all that would be required is to either redish the rear wheel, or at the very most spread (cold set) the rear stays 4mm to accommodate the wider 7 speed, but you would still have to cold set the rear stays if you were going to a cassette. Also with more gears comes a thinner chain which reduces the life expectancy of the chain.

Froze, thanks for the comments. I will just let everything settle and ride the Miyata until something feels off. It rides smooth now accept a wobble in the cassette. I'm not sure what the cause is. I figured if I was going to get a chain whip and cassette removal tool that I may as well replace some parts in the hub.

At far as the BB, I believe it is the 600 series like you say. So you are saying that because it is a sealed unit and is working smooth, that there should be no need to replace it? That is awesome. I just figured with it being 25 years old that it should be replaced, but I guess it was made well.

I am actually going to ditch and sell my AL frame, with brifters and 105 group and use the Miyata as my main bike. It is fast. The bar-ends shift super fast too. They are indexed for 10s, but I can only use them on friction mode. The Miyata fits me better.

That Miyata you have is a superb bike, the frame was the best frame ever made by any manufacture in the world at the time, using a triple butted splined frame that no one was making. The only thing that made the Miyata Pro lighter then the 912 was primarily the double butted spokes and the Araya rims vs straight gauge spokes and Ukai rims; also the Suntour Sprint derailleurs were a tad lighter then 600ex but not significant.

I was wrong about one thing, in the steel frame Miyata choices they did make a Team version I found on the internet that was about 2.5 pounds lighter then yours or the pro, mostly due to tubulars and a lighter fork.

Froze said:

That Miyata you have is a superb bike, the frame was the best frame ever made by any manufacture in the world at the time, using a triple butted splined frame that no one was making. The only thing that made the Miyata Pro lighter then the 912 was primarily the double butted spokes and the Araya rims vs straight gauge spokes and Ukai rims; also the Suntour Sprint derailleurs were a tad lighter then 600ex but not significant.

I was wrong about one thing, in the steel frame Miyata choices they did make a Team version I found on the internet that was about 2.5 pounds lighter then yours or the pro, mostly due to tubulars and a lighter fork.

So should I worry about the wobble in the freewheel? How do I remove the freewheel to clean it up? Do I need a special tool like if I was going to remove the cassette?

nativewisdom said:

So should I worry about the wobble in the freewheel? How do I remove the freewheel to clean it up? Do I need a special tool like if I was going to remove the cassette?

No, actually they all wobble a bit, even new ones! As long as the wobble is up and down and not side to side and the chain isn't jumping gears your fine. Even cassettes wobble a tad.