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Discussion Starter #1
Bought a 2021 TREK Emonda SLR 7 with Shimano Ultegra Di2 for my 18-year old son who is a development athlete. But I was disappointed by the, practically non-existing, clearance between the right crank arm and the chain that has caused the chipping of the crank arm. When the chain is on the big front disc (52 teeth) and on the lower (heaviest) gear (11 teeth) there's barely any space between the crank and the lower part of the chain (there is a 1mm gap when the bike is on the stand but when my son rides the bike and presses hard on the pedals the gap is zero). The seller says that that's the way the bike was when it was unboxed and suggested to use a washer between crank and frame. But is this right? Has anyone had any similar experience? Because other that this setback the bike is beautiful and powerful. If I made this post in the wrong place please let me know. You can also see a relevant video on YouTube at the link below. Thanks.

 

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I assume you didn't buy this from a dealer?
Are you sure this is a real Trek and not a fake?

The seller says that that's the way the bike was when it was unboxed and suggested to use a washer between crank and frame. But is this right?
No that's not right. I do not believe there is room on an Ultegra crank to shim it with washers. Not by that much. There should be about 5mm of clearance.

You really should take this to a dealer. There are multiple things this could be.
a) the frame could be made wrong. (especially if it's a fake Trek)
b) The rear derailleur may be bent outward. A bike shop could fix this.
c) the crank could be installed wrong. On the bottom bracket, make sure the dust covers (Number 1) are installed properly. And on the crank, make sure the rings (Item No 5) are installed properly.


(there is a 1mm gap when the bike is on the stand but when my son rides the bike and presses hard on the pedals the gap is zero)
This is normal. Bikes flex and move when you ride them. Which is why there should be about 5mm, not 1mm.

When the chain is on the big front disc (52 teeth) and on the lower (heaviest) gear (11 teeth)
For reference, the front gears are called 'Chainrings" not disc. And the rear gears are called 'Cogs' or 'Sprockets'.
 

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This is not normal. I would definitely have a bike shop check it out.
 
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Discussion Starter #4
I assume you didn't buy this from a dealer?
Are you sure this is a real Trek and not a fake?

No that's not right. I do not believe there is room on an Ultegra crank to shim it with washers. Not by that much. There should be about 5mm of clearance.

You really should take this to a dealer. There are multiple things this could be.
a) the frame could be made wrong. (especially if it's a fake Trek)
b) The rear derailleur may be bent outward. A bike shop could fix this.
c) the crank could be installed wrong. On the bottom bracket, make sure the dust covers (Number 1) are installed properly. And on the crank, make sure the rings (Item No 5) are installed properly.


This is normal. Bikes flex and move when you ride them. Which is why there should be about 5mm, not 1mm.

For reference, the front gears are called 'Chainrings" not disc. And the rear gears are called 'Cogs' or 'Sprockets'.
Thanks so much for your input tlg. No, this bike is original and in fact one of the first official TREK Emondas that arrived from Wisconsin to this part of the world. The dealer is a very cool guy who is willing to help. I just do know how experienced he is. But I will suggest to him to have a look at the issues you've mentioned above. Will keep you posted on this,
 

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Should not need any spacers at all. The BB90 on Trek road bikes is...wait for it...90mm wide. A standard British bb w/ a Shimano external cup bb is...68mm wide + 2 x 11mm cups = 90mm. While they have certain problems the Trek BB90 is about the easiest thing in the world to work with.
 

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Should not need any spacers at all. The BB90 on Trek road bikes is...wait for it...90mm wide. A standard British bb w/ a Shimano external cup bb is...68mm wide + 2 x 11mm cups = 90mm. While they have certain problems the Trek BB90 is about the easiest thing in the world to work with.
Not a BB90 anymore.





Also just looked at my SLR9, plenty of clearance on both crank arms, and that is with the DuraAce power meter pod.
 

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Not a BB90 anymore.



Yea it's now 85.5mm

c) the crank could be installed wrong. On the bottom bracket, make sure the dust covers (Number 1) are installed properly. And on the crank, make sure the rings (Item No 5) are installed properly.

 

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Discussion Starter #12
OK, so here's an update on this issue. The local TREK representative received a proprietary 1mm-thick washer from TREK. He inserted it into the right part of the crank arm and (obviously) we now have a reasonable clearance between the crank arm and the chain, about 2mm. Having ridden the bike for many many kms, the problem of the crank scratching the chain never surfaced again. The question though is why should this happen in the first place and also if by slightly changing the symmetry of the left and right distances of the cranks to the centerline of the bottom bracket, we create another problem.
 

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OK, so here's an update on this issue. The local TREK representative received a proprietary 1mm-thick washer from TREK. He inserted it into the right part of the crank arm and (obviously) we now have a reasonable clearance between the crank arm and the chain, about 2mm. Having ridden the bike for many many kms, the problem of the crank scratching the chain never surfaced again. The question though is why should this happen in the first place and also if by slightly changing the symmetry of the left and right distances of the cranks to the centerline of the bottom bracket, we create another problem.
There are multiple things this could be.
a) the frame could be made wrong.
If the frame was made wrong, adding the spacer fixed it.
You could measure the pedal spacing and see if it is equal or not.
But 1mm isn't that much. You likely wouldn't ever notice it. You can also compensate by moving your cleat 1mm.
 

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Hmmm. Where exactly did he insert the washer again? Do you mean at the bottom bracket on the drive side? I don't see how 1mm can change the chain line enough to stop the arm from striking the chain.
 
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Discussion Starter #15
Well, I wasn't there when the mechanic inserted the spacer, so I can't answer that. But the matter of fact is that from a literally non-existent distance between crank arm and chain (when at the lowest sprocket of the cassette and at the biggest chainring) we now have a 2mm (+ or -) gap. Which seems to work for now.
 

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What can I say? If it works, it works. Problem solved! (y)
 
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