Rail 9.7 chainring rubbing

[Sean0711]

Also just for reference on my ride this weekend I managed to snap my chain, which I found very strange as the bike has only covered 250miles. It snapped on a flat section as well so not under serious load. I’m gonna assume that the chain ring and chain snapping are linked in some way. Any thoughts?

 

[Paul Mac]

I'm wondering if the rails should have the 53mm off set version of the e thirteen chainring, but shortage of parts means they put on what was available ?

 

[Bomble]

Mine has done the same. At first I thought it might have been a trapped stone or something so I put a sticker over the damage and went out last night.

 

[Mr_Price]

Under certain forces the chain stay pushes up against the chain ring. I don't think this is acceptable. I've done ~25km on mine with a new chain stay and so far no new market but it's only a matter of time.

 

[Mikerb]

Mine has done the same. At first I thought it might have been a trapped stone or something so I put a sticker over the damage and went out last night.

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If you take the chainring off the SRAM model number should be etched on the back and also the offset. The normal chainring to chainstay clearance is 4/5 mm so if the chainring you have fitted is non boost ( 6mm offset) that gap will be down to 1 or 2 mm. The correct offset is 3mm ( boost).

 

[Paul Mac]

I thought it was just the e thirteen chainrings causing damage, not the sram ones as well!

 

[Mikerb]

If you take the chainring off the SRAM model number should be etched on the back and also the offset. The normal chainring to chainstay clearance is 4/5 mm so if the chainring you have fitted is non boost ( 6mm offset) that gap will be down to 1 or 2 mm. The correct offset is 3mm ( boost).

The ref no for the SRAM X Sync 2 chain ring for Bosch motors is CR-XSYNC -BOS- B1

 

[Bomble]

If you take the chainring off the SRAM model number should be etched on the back and also the offset. The normal chainring to chainstay clearance is 4/5 mm so if the chainring you have fitted is non boost ( 6mm offset) that gap will be down to 1 or 2 mm. The correct offset is 3mm ( boost).

Thanks but it’s back at the bike shop so can’t check.

 

[neiloxford]

I suggest letting the air out of the rear shock and checking alignment as the rear moves through the travel. It might be at some point in the travel it gets closer to the chainring.

 

[Axxlrod]

So I'm not the only one!

Was riding this weekend, and I kept feeling like the bike was applying the brakes. Got back home and noticed the chain ring had been contacting the triangle.

The chain ring retainer is tight.

So I can't fathom why this is happening.

Anybody get an answer from Trek or their LBS?

 

[Paul Mac]

So I'm not the only one!

Was riding this weekend, and I kept feeling like the bike was applying the brakes. Got back home and noticed the chain ring had been contacting the triangle.

The chain ring retainer is tight.

So I can't fathom why this is happening.

Anybody get an answer from Trek or their LBS?

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How far away is the chainring from the frame while the bike is static?

 

[Sean0711]

So I'm not the only one!

Was riding this weekend, and I kept feeling like the bike was applying the brakes. Got back home and noticed the chain ring had been contacting the triangle.

The chain ring retainer is tight.

So I can't fathom why this is happening.

Anybody get an answer from Trek or their LBS?

View attachment 57155

My supplying bike store have submitted a warranty claim to trek for me. So am awaiting a response. Will post when I get a reply from them/Trek.

 

[Mr_Price]

Trek sent a new chain stay to my LBS. Same clearance as the old one (<2mm). I have only managed to do another 50km so no further damage yet. I am returning mountain biker that was ~20 years without riding, I am still finding my feet so I'm still mostly tiding blue trails, as my skills come back I don't have much confidence that this will not repeat itself. I was 165lbs so currently not pushing this bike....

 

[Axxlrod]

How far away is the chainring from the frame while the bike is static?

Not sure exactly, but only a few mms would be my guess.

 

[Mr_Price]

Are all these bikes 9.7? Mine has a SRAM chain ring......

 

[Doomanic]

e*Thirteen chain ring on an ally Rail.

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[Doomanic]

e*Thirteen chain ring on an ally Rail.

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Let’s try that again....

 

[Axxlrod]

Are all these bikes 9.7? Mine has a SRAM chain ring......

Sorry. I should have mentioned. My bike is a Rail 7.

 

[Paul Mac]

Let’s try that again....
View attachment 57159

That looks like enough clearance, something is moving.
Are all the bearings tight?
My chainring is as close as yours, but in 3500 miles it hasn't marked at all.

 

[Doomanic]

Mine hasn't marked the swinging arm either.

 

[Bomble]

Mines a 9.8.

 

[Paul Mac]

My 9.8 came standard with the Sram chainring.
I've noticed that there is a spacer Bush that goes between the motor and the chainring.
Those with the e thirteen chainring, have you got any spacer that goes between the motor and chainring, or does it just mount on direct?

 

[Mikerb]

A couple of thoughts which may help to discover what is happening:-

It is fairly easy to check the chainring is not loose and the rear triangle is not moving due to worn bearings so I will assume both are OK.

That leaves 4 things in my mind. First would be a chainring with too much flex...........easy to check by hand.
Second would be incorrect offset. I assume the chainring should be boost/3mm.
Third....and probably associated with offset would be chainline. For example, is the chainring being pulled towards the chainstay when the lowest ( largest) cassette cogs are being used?
Lastly, is the gap between the chainring and the chainstay the same whatever the point of rotation of the chainring? If not that would point to the motor axle not being at 90 degrees to the bike centre.........or the motor able to twist on its mountings. To test the latter some pressure would need to be applied to one then the other crank with the rear brake held on.

 

[Mr_Price]

A quick update. My LBS replace the chain stay. 2 rides later and I had some light marking on there. Took it back to the shop, they were going to start a full warranty claim with Trek. Couple of days later Trek asked them to try a couple of more 'tricks' (no idea what) before swapping out the frame.

With work and riding I didn't get a chance to drop it back for round 2 of checks. Then on Monday I noticed some more damage, nasty this time. I was cleaning the bike when I noticed the main pivot axle was hanging out.

Took it to the LBS, they were great. They have given me a 9.8XT demo bike while we work out a solution.

 

[Mr_Price]

I should have added: all I said to the shop was, "obviously the frame is faulty, or your tech didn't torque the new chain stay on correctly..."

They quickly moved to new bike day discussions.

 

[Doomanic]

My LBS replace the chain stay.

I noticed the main pivot axle was hanging out.

Oh dear, guess who didn't use threadlock and torque the bolt up correctly...

LBS, they were great. They have given me a 9.8XT demo bike while we work out a solution.

Not really great, more the least they could do in the circumstances.

 

[Sean0711]

Nice! I think my bike is from the same batch, as it’s now falling apart. The supplying BS have got trek to agree to replace the chain stay on my 9.8xt. I took the thing apart and found that the motor bolt brackets were loose and the motor bolt themselves. Causing the flex in the motor and chainring which caused the rubbing. Torqued everything back up, no more rubbing, just awaiting the bike shop to pick the bike up and replace the chain stay. 2 more rides since everything being done up and now the main pivot bolt has wound itself out and the tread is destroyed.... thought these bikes were supposed to be bomb proof. ?

 

[Doomanic]

Given how many other bolts were loose I'm amazed you didn't check all the other bolts. I know you shouldn't have to, but under the circumstances it would seem sensible.

All the torque figures are on the exploded diagrams posted as a sticky in the Trek section.

 

[Sean0711]

Given how many other bolts were loose I'm amazed you didn't check all the other bolts. I know you shouldn't have to, but under the circumstances it would seem sensible.

All the torque figures are on the exploded diagrams posted as a sticky in the Trek section.

I did! I had already had to torque the upper main pivot back up once. And yes I shouldn’t have to check thread locked bolts for tightness, espcially on a 4 month old bike that’s only done 250 miles. P.S. the torque figures for the motor mounting brackets to the motor are not on the exploded diagrams.

 

[Bomble]

Mine was hitting on full shock extension. Everything tight and no play anywhere.