Removing shimano FC-MC20 Bottom Bracket Assembly

Worked out how to strip the cranks off a very old Shimano BB, and managed it! Not bad for 68yr old.

It is in a friend's Dawes.

The axle is like a stick in a top hat.

But couldn't remove the LH "adaptor" as my splined extractor just did not shift it! Used a long bar, too!

Should the splined extractor slide easily in? It didn't go in far. It showed no signs of "camming" out, even so.

Should I drive it in with a Mallet, using a heavy block on the RH side to protect the frame?


Didn't even try the RH driven side, as that would possibly be as tough to shift, too.

I presume both sides need to be replaced?

Shop job?

Or soak in WD40 and try again?

Thanks,

Charles

 

As you're talking about splines it sounds like it's a Shimano cartridge BB. And strictly speaking the LH "cup" is just a centering device, you can pull the BB out from the right side. But unless it's worn out, or you need to swap to another axle length, why mess with it? Otherwise the tip is to use a long bolt to keep the splined too from slipping when you crank down on it. Some say a Q/R skewer can be run through the bb axle for this purpose, but I haven't tried that.

Take note of the different directions of threading.

 

Suggest you check the Park Tool website.
http://www.parktool.com/blog/repair-help/categories/bottom-brackets:

"THREADING NOTE: Most modern bikes use an ISO thread standard for the bottom bracket. The left side thread is a right-hand direction thread, which tightens clockwise and removes counter-clockwise. This standard is also called English or BSC. The right side (drive side) thread is a left-hand thread, which tightens counter-clockwise and remove clockwise. There are some exceptions to the ISO. Bikes made in Italy may use "Italian" threading, with both drive and non-drive sides right hand thread. There may be markings such as "36 x 24" on the cups. Older bikes from France may have right hand threads on both sides (35mm x 1mm)." - From Park Tool website

 

The code FC-MC20 refers to an Alivio crank set. But the BB is probably one of the usual Shimano square taper cartridge BBs. I'd be guessing that it is an "english" BSA type (right hand thread on non-drive side, left hand thread on drive side). One thing is certain. The non-drive side will ALWAYS be right handed.
If ever I find a BB which is hard to undo I put the BB tool in a bench vice (as long as the tool has flats) and then place the whole frame and BB on top of the tool and twist. Dramatically increases leverage and places less stress on the frame than if it were clamped by the seatpost in a workstand.
If pressure is needed to hold tool and BB together then get someone to press on it.

... of course you do need a bench vice...

 

Hypothetically, you could leave the left cup in place and simply turn out the reverse-thread right cup. The new BB cartridge could then be fitted and tightened against the old left cup. You would need to be careful that you were tightening the BB against the left cup and not the right-side BB shell face. If the latter, you might break the flange off the right cup. It would still work, even if you did this, but your chainline might be out a little.

Rude question: do you actually need to remove the BB?

 

Thanks, good people!

This is all very encouraging; the tips are great.

I don't have the bike to hand - but there was a vast amount of play! The cranks were well fixed to the BB axle.

Although I didn't remove the RH crank there was no visible evidence that the RH cup was loose.

I could only surmise that a replacement BB is needed.

Is there another possibility?

And I don't think your question was rude!

 

Yup, the question is a little rude for sure.

 

Quote: Originally Posted by charlesb .

... but there was a vast amount of play! The cranks were well fixed to the BB axle.

Although I didn't remove the RH crank there was no visible evidence that the RH cup was loose.

I could only surmise that a replacement BB is needed.

Is there another possibility?


First off - Given that you are talking about splines, what you've got is a cartridge BB. For all intents and purposes there's no point in talking about "cups". From the casual mechanic's perspective a cartridge BB consists of two parts, one cylindrical bit with a splined flange at one end and the axle & bearings inside, one ring with a wedge shaped cross section and a splined flange at the base. The cylinder (AKA the cartridge) goes in from the right and the wedge-shaped ring goes in from the left to stabilize the narrower end of the cartridge.

You might want to do an image search of "square taper cartridge BB" to see what you're up against.

Next - Shimano cartridge BBs are just about always very good value for money. It's a bit unusual to wear them out to that point, but not impossible. I think I've come up against a grand total of 2-3 units that were worn out to the point of actually compromising functionality.

And last - no, I can't think of any other reasonable diagnosis.

 

Thanks, Dabac.

Your description beats Shimano's attempt at conveying to me what I want to visualise! ;-)

It's good to have a view on their value for money, too.

("cups" was harking back to days of yore, struggling with cotter pins and nice big ball bearings which raced around those bits that screwed into the Bottom Bracket shell; one had shallow flats, and another was adjustable with a notched locking ring.)

 

I disagree - everyone I have ever dealt with, professional or otherwise, calls the fittings at either end of the cartridge a "cup". Legacy of the terminology of the old free-bearing system. Minor point, but I don't see any point in being pedantic about it.

 

Perhaps some context and explanation is required. Although I have removed Shimano cartridge BBs frequently, I have never needed to remove one because it was worn out. The Octalinks are an exception, as they have much smaller bearings, and I have managed to wear one until it developed just the tiniest bit of roughness when you examined it carefully, but it died due to its spindle getting bent in a crash before I could wear it out. I have never known a Shimano cartridge BB to develop play, but I'm sure that they could if used sufficiently -it's just rare that it happens. So, I certainly think that it is a fair question to ask whether this BB requires removal. I think that it is much more likely that the crank sockets are deformed - a very common problem. That would be my guess diagnosis.

 

I disagree - everyone I have ever dealt with, professional or otherwise, calls the fittings at either end of the cartridge a "cup".



Well, not where I'm at - Over here it's "bottom bracket" and "ring".

 

Wish I had found this site a week ago,when I knew nothing about BB 's
For the record I am 66yrs and had a BB experience recently which was so enthralling I had to blog it.
I do know a lot more now.
If you like to share and maybe learn a little..
Go here http://servicingthebottombracket.blogspot.com/2010/11/servicing-bottom-bracket-on-my-bike.html
Enjoy the ride.

 

I have just read your blog entry. Just a word of caution, in my experience a "creak from the bottom bracket" is rarely actually coming from the bottom bracket. On the occasions when it is, it is usually fixed by taking out the BB, cleaning its threads, cleaning the BB shell threads, and reinstalling the BB to the specified torque with anti-seize compound (or Loctite) in the threads. 8500 km should not have worn out a BB, even an Octalink one such as yours.

 

Tks Arte for your comments...I think you are on the ball.
All sounds very logical. Hopefully strange noises will go away and leave me in peace./img/vbsmilies/smilies/smile.gif
Kenno

 

strange noise?? Hope evertything goes well now.