Bicycle Mechanics - BB bolt question

does anyone know what the size and thread of the bolts are that attatch the cranks to a Shimano UN52 BB? i have the BB but no bolts to attatch the crank on with. this is my first attempt at attatching a crank to a BB. can i just put the cranks on there and torque the bolts down or do i need special tooling like everything else i ever have to do to my bike ?

I don't know the thread size right off hand, but to install the cranks, you'd need the proper socket for the bolt. A standard, run-of-the-mill socket and handle will work fine. Now, you will need a "crank puller" to remove the crank from the bottom bracket spindle.

actually, i found the original bolts that came out of the cranks so im good to go. just checking to see if there was something special i had to do to put the cranks on.


thanks

actually, i found the original bolts that came out of the cranks so im good to go. just checking to see if there was something special i had to do to put the cranks on.


thanks


There should be a washer for each bolt, too. Also, I usually place a little grease on the flats on the spindle to help crank removal at a later time.

Never... ever... grease the tapers on a square-taper BB axle. The arm will slide too far up the taper. I worked in a LBS for 7 years and I never saw a crankarm that wouldn't come off because of corrosion or other issue that grease would solve... it doesn't happen.


just checking to see if there was something special i had to do to put the cranks on.


Yes there is... don't torque the bolts super-tight and put a tiny bit of grease on the threads.

Tapered axle crankarms require a bit of a feel as far as how tight is tight enough. Too tight and you'll slide the crankarm up the taper to the point where it will damage the square hole in the crankarm and probably never stay tight.

It's hard to explain how tight to make it without a torque wrench without showing you in person. I've done 1000's of 'em "by feel". Tighten the bolt until you think it's snug then maybe another 3/4 of a turn. Check the bolt after the next two rides to see if it's looser than you tightened it to. If so, then snug it up again.

Go to your LBS and ask for a set of crank bolts. :)

Never... ever... grease the tapers on a square-taper BB axle. The arm will slide too far up the taper. When will this fairy tale ever stop?

It's hard to explain how tight to make it without a torque wrench without showing you in person. I've done 1000's of 'em "by feel". Tighten the bolt until you think it's snug then maybe another 3/4 of a turn. Check the bolt after the next two rides to see if it's looser than you tightened it to. If so, then snug it up again.How about recommending the correct torque for them that don't have a well calibrated elbow? repair section at www.parktool.com is a good place to start.

How about recommending the correct torque for them that don't have a well calibrated elbow? repair section at www.parktool.com is a good place to start.

Blow me. If he had a torque wrench then we'd play your little lookup game. He doesn't so I'm giving him some useful guidance rather than having him think you just crank the bolt until it stops.

Blow me. If he had a torque wrench then we'd play your little lookup game. He doesn't so I'm giving him some useful guidance rather than having him think you just crank the bolt until it stops.Oh My!! Why doncha take a chill pill and put your head on straight. If one knows the proper torque and the length of the wernch handle he is using it's alot less of a mystery.

Hmmmm....I'm not wanting to interrupt the pissing match, but I also don't grease crank tapers. Perhaps a better way to put it is yes, you can grease tapers, but the grease makes it much easier to enlarge the crank hole and ruin the crank if you overtorque the bolts. If you thoroughly clean the tapers and crank hole before installing with the proper torque, it shouldn't creak. It is very common for folks that have creaking crank issues to tighten and tighten again, rather than pulling the crank and cleaning out contaminants. I do however reccommend greasing the threads on the crank bolts, as this will allow one to attain the proper torque, and prevents seizing. If grease isn't your thing, anti-seize compound is another option that doesn't tend to allow crank tapers past the point of "no return".

On the bright side of things, I have fixed "ruined" overtorqued cranks by cutting a shim from an aluminum soda can and placing it on the taper before retorquing the cranks. I bought the somewhat rare 180mm XT cranks for my utility mountain bike (ab)used, and fixed this way, they've been going strong with no creaks (or grease) for 6 years now.

Hmmmm....I'm not wanting to interrupt the pissing match, but I also don't grease crank tapers. Perhaps a better way to put it is yes, you can grease tapers, but the grease makes it much easier to enlarge the crank hole and ruin the crank if you overtorque the bolts. It's simply the greaser non greaser debate that will never end,and it just shouldn't be drug out. I've always used grease and never an issue.Also curious that new issue shimano square taaper BB come pre greased. Maybe it's jsut another big shimano conspiracy.

It's simply the greaser non greaser debate that will never end,and it just shouldn't be drug out. I've always used grease and never an issue.Also curious that new issue shimano square taaper BB come pre greased. Maybe it's jsut another big shimano conspiracy.
OK, then we'll agree to disagree on this one, eh? ;)
I see your point Sydney, that F1-Fan was saying that you should "never" grease tapers. Grease or no grease preferences aside, the only unilaterally true statement would be, "never overtorque crank bolts".

FWIW, I was always a "non-greaser" but after reading numerous posts on the Forum I think it just might be an old wive's tale (w/ apologies to any old wives out there).