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Old 06-24-10, 10:12 PM   #1
fishingjld
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What size bottom braket, and which cranks should I use????

Ok I have a 1991 (I think) Giant Iguana (no it doesn't bite) and I have a decent amount of wobble in my bottom bracket when I grab the pedals and shake. I need to know the pertinent info for a new bottom bracket. I have been told it is english, 68x118??? Is there any other info I need to get a new one? Do you have any recommendations on a make and model of bottom bracket? Next I would like to know what measurements and make and model crankset would fit my new bottom bracket. The crank that is on the bike now is a Sakae Enhanced Ovaltech 48x38x28. I took the chainrings off today and cleaned them and they are pretty ate up. Thanks in advance for all the info.
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Old 06-25-10, 12:13 AM   #2
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Originally Posted by fishingjld View Post
Ok I have a 1991 (I think) Giant Iguana (no it doesn't bite) and I have a decent amount of wobble in my bottom bracket when I grab the pedals and shake. I need to know the pertinent info for a new bottom bracket. I have been told it is english, 68x118??? Is there any other info I need to get a new one? Do you have any recommendations on a make and model of bottom bracket? Next I would like to know what measurements and make and model crankset would fit my new bottom bracket. The crank that is on the bike now is a Sakae Enhanced Ovaltech 48x38x28. I took the chainrings off today and cleaned them and they are pretty ate up. Thanks in advance for all the info.
If you're getting a bottom bracket and crankset together, you know all you need to know right now: the bike is English thread. After that, the BB should match the crankset.

"68 x 118" means the bottom bracket fits a 68mm width shell (standard English) and the spindle is 118mm long. You don't need to know the length of the existing spindle if you're going to change the BB anyway, but that length is correct for a Sakae crankset of that era.

Gotta look out for those Giant Iguanas. They'll eat anything.
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Old 06-25-10, 07:00 AM   #3
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Not correct. You should get a 118 or close to it again, so that you don't change the chainline significantly.
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Old 06-25-10, 07:36 AM   #4
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Wow

Thanks for the information guys!!! Do you guys have any you would recommend that include a bottom bracket?
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Old 06-25-10, 07:41 AM   #5
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I would look around the web for the best deal, or even CL
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Old 06-25-10, 07:50 AM   #6
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Most cranksets do not include a bottom bracket. A 1991 bike might still be using a cup and cone bottom bracket which means you may be able to get away with some new ball bearings, some grease, and a proper adjustment. As for the crank, it's almost always cheaper to buy a whole new crank than to replace chainrings. However, are you sure your rings are worn out? Chainrings often have strange features on the teeth in order to aid shifting. A LOT of people mistake these features for damage or wear.

If you just want something cheap, go to www.niagaracycle.com and sort cranksets by price. There are some dirt cheap Shimano options that use non-replaceable steel chainrings riveted to the crank. You may need a different bottom bracket length though so be sure to confirm that spec before ordering anything. Again, Shimano makes some dirt cheap cartridge bottom brackets that will work just fine, if you need one.

If you are looking to upgrade, all of the "better" cranksets these days use outboard bearings, a completely different style of bottom bracket than your current bike. for those cranks, you buy the crankset and a set of cups with bearings. The chainline is fixed so no need to worry about spindle length.
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Old 06-25-10, 01:25 PM   #7
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Ok so I have found out that I have a 68x118 bottom bracket with square taper. My crank arms are 175mm. If I found a new style crankset with all the correct measurements above will it work. I ask this because I have a bottom bracket now that has a stud running through the spindle with a nut on the end holding the crankarms on the bike. Will getting different tooth? patterns for the chainrings matter? I have only found one 48x38x28. There are many other different ones with different tooth patterns though. I am assuming that it will as long as I adjust my front derailleur's limits right????? Also some of them say for 10 speed, 9 speed, 8 speed. I have a 6 speed rear total 18 speed. God this is so confusing.
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Old 06-25-10, 05:40 PM   #8
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i just need the one question answered PLEASE!!

So really I just need the my last question answered. If say a Shimano Alivio meets all requirements except it says it is 9 speed compatible, will it be 6 speed compatible too?
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Old 06-25-10, 05:48 PM   #9
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A new crankset would likely require a different bottom bracket than 68x118 square taper. So don't get a new BB until you've decided if you're going to get a new crankset.

You can probably use different tooth counts. I replaced the 48x38x28 triple on my old MTB (also 6-speed) with a 44x32x22 crankset. But at the same time I replaced the cassette so that my top gear stayed about the same while my low gear dropped by quite a bit. I use the same front derailer but I had to lower it by about 8mm and the back of the derailer cage now almost hits the chain stay. One thing I've noticed about the smaller chainrings is that they wear much quicker (except for the 22 which is steel). I never replaced the rings on the old crank but am already on my 2nd 44.

The Alivio will work in a 6-speed drivetrain. The crank I have is a Deore LX "9-speed". I use 7/8-speed chains and it works fine.
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Old 06-25-10, 05:56 PM   #10
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thanks gonzo bob. maybe i should just keep the same crank. joejack951 earlier posed the question on whether they were actually worn. I am not sure myself now. I think all the adjustments you had to make may be a little much for a newbie like me. I work on cars for a living so a remove and replace is doable but adjustments not great with that yet. The crank has rust spots on it too so i guess i wanted to upgrade for that reason too. I am looking at the Shimano UN54 bottom bracket I think it will work. Thanks alot for all the help.
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