goldfinch

I have a Giant mountain bike of uncertain vintage. The bottom bracket was shot. i removed it and the triple crank, which had some years of bleached out ugliness. I decided to replace them with a triple crank and bottom bracket I got from a friend who had taken them off a mountain bike when doing a 1x conversion. The crank has the same gearing. My bike has an odd front Acera deraiileur that acts as a spacer between the bottom bracket and the crank. It is pictured below. I first tried installing the bottom bracket and crank without that derailleur and use da different front deraiileur. Well, the crank ended up too far in messing up the chain line and the front deraiileur wouldnt operate correctly. So, I assumed the spacer was necessary. It seemed like the 73mm bottom bracket shell needs that extra spacer. I then reinstalled the old weird front deraiileur, the bottom bracket and crank but before I got the crank up to the torque specs I could see that the axle stiffened up and would barely turn. I started over in case of operator error but same thing happened.

What might be going on?

I sure seem to be running into a lot of "first time for me" problems lately.

Andrew R Stewart 

That "spacer" is how the ft der is mounted. It's called the "E" type. The BBs that are to be used with this bracket are also references with an "E". This has nothing directly to do with a 73mm shell width except that more MtBs have that shell width then road bikes do and I know of no road bike specific ft ders that are "E" mounted.

As cartridge (or press fit bearings for that matter) are installed there's a compressive force acting on the bearing. The more worn the bearing is the more this installed compression force will be noticed. But I also wonder if more is going on then just that. "but before I got the crank up to the torque specs I could see that the axle stiffened up and would barely turn" So dud the BB turn smoothly before the old crank arm was installed? If so then I suspect some rubbing between the crank and the BB or frame is happening. It is possible that the crank arm now pulls up too far on the BB axle's taper and is contacting the bracket. Andy

goldfinch

The bb spindle turned smoothly before the install. When I tried installing without the E type front der the spindle turned fine but I couldn't get the replacement deraiileur to work, the crank was too close the the BB. But, the spindle turned freely. When I added the E type front der back in, that is when I had problems with the crank not turning. I guess I should have checked to see if it was rubbing on the der mounting.

Suggestions for next step? Do I need a different BB, the E type? This was very educational.

goldfinch

Supplemental questions: I made the error of throwing the old BB away as I planned to put on a matched set of a standard square taper BB and crank. Now that wont work. How do I determine the proper size of the E type BB for the bike? Will I be able to use the crank that I originally tried to use?

​​​​​​Or, instead of getting a "E" type BB, can I add a spacer to the new BB and use a different derailleur? Wonder if I still will have the problem of the crank not going around.

goldfinch

I am trying to figure this out. I think that if I want to use the triple cranks that I have I would need an E type bottom bracket, 68mm with a 122.5 spindle. Shimano BB-UN300-E would be it. But, they are not available anywhere that I can find. There are plenty of E type bottom brackets with 68 shell and 113 spindles. Any way to find a crank that would fit? Any way to change the front to a wide narrow single chain ring and ditch the front deraiileur?

Andrew R Stewart 

If the crankset informational sheet (or the listing of it that the manufacturer hopefully provides) doesn't suggest the one or two BB axle lengths that it wants (sometimes AL or OS seat tubed frames need a longer axle) then test fitting BBs is the best way. It seems that the replacement BB you have is too short an axle (hence the der adj range being violated and the likely rub on the E bracket) you could try to add spacers on it's RH side to test the added amount of length you will need. Remember that the axle will be 2x the added spacers amount.

This shows one of the rules in a pro shop- don't toss out old parts till after the new are confirmed. My post (#2) assumed you still had the oem BB. Andy

goldfinch

I am pretty sure I need a 122.5 spindle to use the original crank or the replacement triple I had from a different bike. But there are no E types available with that spindle length. I ordered some spacers but that seems like a long shot. I am surprised at how many cranks do not list the proper bottom bracket spindle size needed.

goldfinch

After hours googling I found a E style bb that has a 123 spindle length. Ordered and hoping.

goldfinch

The BB I ordered turned out to not be available. I remain stuck with a bike with no BB that fits.