Shimano GRX chain issue

[Dakrisht]

New to the forum so hello from sunny SoCal.

I've been riding a brand new GRX-800 series group on a Diverge Carbon and have a strange noise coming from the drivetrain that I simply cannot isolate.

1) The front and rear derailleurs (limit, tension, derailleur hanger height, etc.) are adjusted to the T by both myself (initially) and confirmed by a Shimano tech at the shop.

2) However, when in certain gears, I'm getting a strange chain noise (although I wouldn't necessarily call it chain-rubbing-the-front-derailleur) noise.

Configuration:

- Small ring in the front (trimmed or not trimmed)
- Largest cog in the back + 3 smaller cogs below it

During each revolution / pedal, I'm getting a "slightly noisy chain."

Chain has been degreased and thoroughly lubed.

I'm not seeing any chain rub on the H/L chainring positions trimmed or not (unless seriously cross chaining, there'll be a rub obviously).

But when in the small ring upfront and highest + 2-3 below it gears in the back - damn noise.

Thoughts?

[pdlpsher1]

I also have a Diverge. Great bike. Congrats. Some Shimano chains are uni-directional. Check to see the Shimano logo on the chain is facing away from the bike. Also check the derailleur hanger alignment. These are the first things to rule out.


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[alcatraz]

Adjustments in the stand shouldn't be seen as the last and final. When your body flexes the frame you might need to adjust a bit further. Bring a tool with you on a test ride. Make a small adjustment and go for a spin.

Also check for bent chainring teeth, chainrings out of true, axial crank play etc.

[Dakrisht]

I also have a Diverge. Great bike. Congrats. Some Shimano chains are uni-directional. Check to see the Shimano logo on the chain is facing away from the bike. Also check the derailleur hanger alignment. These are the first things to rule out.


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Thanks! Yeah, totally fantastic bike. Just threw some new Roval Carbon wheels on it. Can't stop riding it, GRX group is solid, frame is stiff, FutureShock 2.0 actually helps a lot. Just a super comfortable, capable, bike. I'm neglecting my Bianchi Infiniti badly these days. Ha.

Chain is good. SH logos on the outside. Hanger seems good too. Will tune again per the Shimano dealer manual, but I'm just not seeing any rubbing even in the extreme cross chain scenarios. Weird.

[Dakrisht]

Adjustments in the stand shouldn't be seen as the last and final. When your body flexes the frame you might need to adjust a bit further. Bring a tool with you on a test ride. Make a small adjustment and go for a spin.

Also check for bent chainring teeth, chainrings out of true, axial crank play etc.

Good call on in-ride tuning. Will do this tomorrow.

Crank, chainrings, all of it - brand new more or less; bike has 200 miles on it since I got it. Will take a closer look but I wonder if this is the skid plate on the inside of the derailleur hanger that's touching ever so slightly...

I'll do another H/L stroke adjustment.

Cable tension seems fine also.

[alcatraz]

New or old makes no difference really. Something could be moving, that shouldn't move. Maybe the crank preload was set poorly, etc. Maybe someone dropped the bike on the chainring putting it down without wheels. Maybe the crank spider has a manufacturing defect that produces wobbly chainrings.

Doesn't hurt to have a look if the problem remains.

[Dakrisht]

New or old makes no difference really. Something could be moving, that shouldn't move. Maybe the crank preload was set poorly, etc. Maybe someone dropped the bike on the chainring putting it down without wheels. Maybe the crank spider has a manufacturing defect that produces wobbly chainrings.

Doesn't hurt to have a look if the problem remains.

Agreed. Definitely a few things mentioned above to potentially dive into with the help of the shop.

Curious about incorrect crank preload and what effects that would have - would it be just noise? Or more?

--
Tonight's update

I'm beginning to think that the "noise" could simply be related to the chain (and the chain plates / rivets) interacting with the teeth of the crank when cross chaining. Think small ring / biggest cog in the back.

I.e. when not in a straight line, the chain will skew a few degrees away from the teeth of the big/small chainring up front and create noise.

Now I also might simply be insane in thinking that the front chainring should be dead or close to dead quiet.

I took my Ultegra (R8000) bike and compared them side to side, the Ultegra is a bit quieter.

I spent a solid hour tonight re-adjusting the front mech on the GRX bike like a Swiss watch. Everything is perfect down the millimeter. High, low, trim, no trim, cage angle, cage height relative to chain, cable tension - all perfect.

Chain is always 0.2-0.5mm away from the skid plate or the inner plate of the cage depending on gearing.

The front mech is perfect.

I also degreased the entire chain and switched to a new lube (Rock 'n Roll Gold) vs. Muc Off C3 Ceramic.

Cleaned the bottom bracket, some sand and debris there, some lube on front mech pivot points as well.

So it is quieter, and maybe I'm just nuts.

Video next

[rollinslow]

Don't forget to check the derailleur hanger alignment.

[robbosmans]

Newer shimano drivetrain are also just louder, especially at when in the big ring and in a easier gear in the rear.

[kode54]

possible that the chain line is off? Either spaced out too much or too little.

[alcatraz]

Shimano grx has a 46.9mm chainline.

Standard road has 43.5mm chainline.

It means that if you install it on a road bike your chainrings are going to sit ~3.4mm farther right and will aggravate the low gear crosschain situation.

It would mean that there must be special rear wheel hubs that allow for the cassette to come out to match that new chainline.

Edit: I read that they didn't adjust the chainline for the hub. Just the crank. That's odd. I'd think everyone would have excessive noise and wear when crosschaining in the big chainring.

[alcatraz]

With correct preload I mean just any preload basically so that the crank spindle isn't moving axially left/right in the bb.

[alcatraz]

On second look at that crank it looks like it could perhaps be possible to offset the chainrings with spacers. Both chainrings mount to the inside of the arms which is different from most road cranks.

I don't know if offsetting by a whooping 3.4mm is possible but maybe something can be done. You will likely need new bolts if you attempt a large offset.

[kode54]

Yes. I was about to suggest spacers.

[DaveS]

The grx chainline is only +2.5mm. I have used spacing washers to correct the chainline on my road bikes with force axs drivetrains. I used McMaster-Carr 98370A015 washers. I've also modified thinner washers and used two to get the desired 2.5mm. My 46/30 cranks needed longer bolts, but the 48/31 cranks had a little longer bolts that still provided 5 turns of engagement.

I have no noise issues, regardless of the gear combo. Hollow crank arms don't create noise.