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Discussion Starter · #1 ·
I have about 1000 miles on my 2008 Madone 5.5 and the crank axle has developed a significant gap between the axle OD and the bearing inner race ID. Tightening the left crank axle bolt seems to snug things up (this is what the LBS mechanic did) but soon the assembly loosens up again such that the lateral play as measured at the crank arm is about 1/16 inch. (grab both crank arms and rock them back and forth)

Has anyone else had this problem? Fix? Am I completely misunderstanding what is going on here?
 

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AJK said:
I have about 1000 miles on my 2008 Madone 5.5 and the crank axle has developed a significant gap between the axle OD and the bearing inner race ID. Tightening the left crank axle bolt seems to snug things up (this is what the LBS mechanic did) but soon the assembly loosens up again such that the lateral play as measured at the crank arm is about 1/16 inch. (grab both crank arms and rock them back and forth)

Has anyone else had this problem? Fix? Am I completely misunderstanding what is going on here?

I am assuming you have the Bontrager crank?

Not that it matters.

1) There should be no lateral play there at all, in that you are correct.

2) But are you merely getting side to side play? As opposed to up and down play? If the former, then it sounds like a crank issue, and a warranty replacement of the crankset with your LBS. If the later, then you possibly could have any one of a number of issues, some of which could involve the frame itself.

If you could be more specific.

zac
 

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Discussion Starter · #4 ·
Yes, I am saying that the ID of the bearing is larger than the OD of the spindle.

Actually, I don't understand how this system is supposed to work. There seems to be no provision for adjustment as there was in the old BB assemblies. I would think that the spindle and the bearing should be a very close fit. Not a press fit, but just short of that. Then for side to side play (ie, along the axis of the spindle) there should be a provision for shims, otherwise once the left crank arm is tightened, the crank assembly could be either too loose or worse, too tight, squeezing the two bearings together. I can't believe that the whole thing is designed to be so precisely made that you just bolt it together and it's right.

Also, when I took the bike back the the LBS that I bought it from, they said that this sort of experience was common and the advice from Trek was to merely take it apart and put it back together again a few times and it wound then stay tight. It hasn't.

Is there a torque value for the crank arm?

So, bottom line, I can't make any sense of this. I was hoping that this was a common issue with the new precision molding of the Madone frame in the area of the BB and the head tube bearings and that a proven fix was available.
 

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My 5.5 pro did the same thing, I think that it came that way from the bike shop. I took it off and put it back together and it seemed to get rid of the play that was there, now about 1000 miles later there is no play but there seems to be a popping sound coming from the bottom bracket. I have checked all of the bolts and can't find any that are loose. I went for a 113 mile ride today and it did not start until I hit about 60 miles. The crank seems to turn just fine. I guess I will wait until it gets worse
 

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Well, yes, the left crank is merely tightened along the spindle axis until there is no play. Sort of the same feel as to how the old square tapers were set: tighten in until no side to side play, but not too much so as to cause binding/grinding.

I am troubled that these are working loose though.

Also, there should be absolutely no play between the bearing and the spindle. It should be a snug, but not press, fit.

I am wondering if the wrong bearings somehow found there way on your machine?

zac
 

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zac said:
Well, yes, the left crank is merely tightened along the spindle axis until there is no play. Sort of the same feel as to how the old square tapers were set: tighten in until no side to side play, but not too much so as to cause binding/grinding.

I am troubled that these are working loose though.

Also, there should be absolutely no play between the bearing and the spindle. It should be a snug, but not press, fit.

I am wondering if the wrong bearings somehow found there way on your machine?

zac
It's my understanding that the Madone BB's use standard sized bearings. If that's the case, couldn't your theory be tested by using loose ball bearings in the BB, then reassemble and check for play?
 

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Discussion Starter · #8 ·
bigjohnson54 said:
My 5.5 pro did the same thing, I think that it came that way from the bike shop. I took it off and put it back together and it seemed to get rid of the play that was there, now about 1000 miles later there is no play but there seems to be a popping sound coming from the bottom bracket. I have checked all of the bolts and can't find any that are loose. I went for a 113 mile ride today and it did not start until I hit about 60 miles. The crank seems to turn just fine. I guess I will wait until it gets worse
I have the same popping sound on occasion. Mostly though what I get is the sound of the chain rubbing the front derailleur when climbing a hill.
 

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PJ352 said:
It's my understanding that the Madone BB's use standard sized bearings. If that's the case, couldn't your theory be tested by using loose ball bearings in the BB, then reassemble and check for play?
No. It uses standard sealed bearings for the particular crank.

It's not a theory, that is the way it is done.

zac
 

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zac said:
No. It uses standard sealed bearings for the particular crank.

It's not a theory, that is the way it is done.

zac
I know the bearings are sealed. I merely suggested that loose balls of the correct size could be substituted. If not, then - oh well!

BTW, this was the 'theory' I was referring to:
zac said:
I am wondering if the wrong bearings somehow found there way on your machine?
 

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No theory, if the bearings don't fit snuggly as I said, then it's the wrong set, or they are deformed or compromised.

Loose bearings will not work, as the OD of the various bearing sets are made to fit the precision sockets of the BB shell. ( as an aside Campy required an adaptor sleeve to fill this OD, but not sure if that is still required. )
 

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Discussion Starter · #12 ·
I'm going to disassemble the whole thing and take some accurate mesurements. I think either the spindle is wrong or the bearings are wrong. No way this could be wear in only 1000 miles. I am not that strong a rider.
 

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AJK said:
I'm going to disassemble the whole thing and take some accurate mesurements. I think either the spindle is wrong or the bearings are wrong. No way this could be wear in only 1000 miles. I am not that strong a rider.
Good idea. I was thinking that even if you just got the left crank off then moved the spindle up/ down/ sideways, you'll see where the play is. I would think it's either going to be between the spindle and bearings or bearings and socket. Isn't that essentially the entire assembly?

Whatever you find, seeing as this is a recurring problem, I think you should get the LBS and Trek involved. I can't imagine that ultimately one of the parts in question won't need to be replaced.
 

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Discussion Starter · #14 ·
Ahh. Now it all makes sense!

It is always difficult to describe something mechanical without a drawing, which is why engineers can't talk without a pencil in their hand, but I will try to paint a word picture of what is going on with this BB assembly.

First let me say that if you are old school, like me, forget everything you know about botton brackets. This is different. This assembly consists of two sealed bearings (and they are radically different from each other) a spindle which is splined on the crank arm side and bolted to the chain ring spider on the other side, a rubber dust cap on the chain side and a steel dust cap on the crank arm side. A captive hex bolt on the crank arm holds the whole thing together.

About the two different sealed bearings. Both appear to have a slip fit between their outer races and the structure of the carbon frame. I say "appear" since the crank arm side bearing came out easily while the one on the other side was tight. I saw no need to force it out. The inner race of this bearing has an ID of .9435 inches. The crank arm side bearing has an inner race ID of .872 inches AND the inner race extends axially about 1/8 inch toward the chain ring!

OK, now for the spindle. It has three different diameters. At the chain ring side it measures .9430. This is a nice fit with the bearing ID (above) of .9435. This means that there is no play on the chain side. The center non precision diameter is .936 inches. The diameter at the splines is .862. Compare this with the ID of its bearing (above) of .872 and you can see why you can have a loose spindle on the crank arm side.

Here is the important part. Remember that 1/8 inch extension of the inner race? When the crank arm bolt is properly tightened the crank arm presses against the dust cap which presses against the bearing inner race which presses against the step on the spindle where the diameter changes from .862 to .936. When this happens, the crank, spindle and the bearing are solidly locked together and all play is eliminated and nothing is over stressed. Quite elegant, actually.

The trap you can fall into is when the hex bolt appears to be tight it may only be tight between the crank arm and the splined part of the spindle and not yet pressing the inner bearing race against the step on the spindle. On my bike it takes 30 lb-ft of torque to properly seat the assembly.

And that my friends is how it works.

Or if you like, tighten the bolt to 30 lb-ft and you're done.
 

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AJK said:
I have the same popping sound on occasion. Mostly though what I get is the sound of the chain rubbing the front derailleur when climbing a hill.
I had this too on my 08 5.2.
I fixed alot of the problem by playing with the rotation of the FD.

My small ring large cog combo still rubs a bit.
but I've learned to accept that this is just the limitations of the machine..:rolleyes:
 

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Switch to a Shimano crank and secure the bearings with a loctite holding compound, check the bearings frequently for roughness, especially after the bike gets wet....... and good luck!
 
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