Ultegra 6800 group dropping chains off big ring without shifting - how come?

[alcatraz]

Hi ww's...

I got a strong heavy friend on a Madone that I built up for him. He is dropping chains off the outside of his big chainring a lot - without shifting.

Usually after a sprint when he sits down. I've never heard of such a thing. Derailleur looks fine (close to rings, in line with big ring) and limits set appropriately (any tighter and it won't shift into the big chainring with lever bottomed out). Crank has no side play and bolts are all torqued.

Chain and chainrings are in good condition. It's a full ultegra 6800 groupset with a compact crank. Cassette was also upgraded to an r8000 11-34t and rear derailleur as well. The chain is a shimano HG701.

Should I check the chainring bolts maybe? They werent fiddled with, should be all originally installed by shimano.

Is the chain too long? I sized it with the shimano manual method.

Just did the chain/chainring wear test by trying to pull it away from the big ring and it doesn't lift anything almost, no light between ring and chain. Seems like a perfect fit.

Have you heard of such a thing? Any ideas?

[mattr]

Freehub drag?

Sits down, stops pedalling, draggy freehub allows too much top run slack. Chain off.

[kode54]

is the chain in the correct orientation? i think the HG701 chain may be similar to the HG901 where the stamped info faces out, rather than inwards. so its a directional chain.

[kode54]

in the picture, the drivetrain looks like it hasn't been cleaned...at all. could need a cleaning to first determine if that's the issue so you can actually see how the FD cage is in reference to the chain. the angle of the FD cage may be skewed a bit which will drop a chain to the outside.

[alcatraz]

Good idea with the freehub.

It looks dirty yes but it's waxed with lots of excess wax.

Thx for the replies. We'll check it out if it's a chain tension vs sticky freehub issue. It does happen more in big/small which means it is the lowest chain tension on the big ring.

When building the bike, almost all the parts were used but working fine. New were chain/cassette/rd/cables.

Because I noticed the 6800 fd actually rubs the chain in 34-34 and there wasn't enough chain clearance in 50-11 I had to angle the fd to set the outer plate parallel to the chain in 50-11 to minimize chain rubb in 34-34. Of course with all the limit screws loosened, and with the cable tension set so outer plate barely touches the chain and then adding a tiny twist of tension to eliminate it. Afterwards I set the limit so that the chain just barely makes the shift up to the big ring.

[jerbax18]

does he backpedal after a sprint? maybe a misaligned derraileur hanger towards outside.

[alcatraz]

Yes I think he said he does maybe backpedal a little.

Thanks for the replies people..

[mattr]

It looks dirty yes but it's waxed with lots of excess wax.

Thx for the replies. We'll check it out if it's a chain tension vs sticky freehub issue. It does happen more in big/small which means it is the lowest chain tension on the big ring.

I could be a combination of all three TBH. Sticky freehub, sticky chain, low tension (and the backpedalling)

First stop would be to clean the whole driveline though. Check for damage/alignment.

[mattr]

Actually, thinking about it, i had a similar issue on an MTB many moons ago when a freehub seal wasn't fitted properly. Sprint and coast in the middle of the block would leave the chain doing all sorts of odd things. At the extremes of the block it would either drop down between tyre and stay or try and tie itself round the front mech. But with it being one of those M952 articulated mechs (MASSIVE sideplates, very small gap) there would be no way for the chain to unship. Got worse in muddy conditions.

And i don't backpedal.

[alcatraz]

Checked cassette, chainring/chain/cog wear. Looks good.

I noticed the right heel of the rider comes close to the chain and it's possible we found the problem.

When sitting down and being to the right of the cassette, the heel is touching the chain and giving it a small backpedal. That derails the chain off the chainring. The right shoe also has some (not a lot) of chain wax on it.

It doesn't explain the chain being thrown to the right though.

It's a fairly new rider so there are some habits that could use polishing.

Right now I'm wondering if there are look cleats that come with an offset so that the foot can sit a few mm further out. Like a high Q factor cleat.

On time cleats it's easy because you just swap left and right to produce a Q-factor shift.

Are there such look cleats?

[TheKaiser]

Right now I'm wondering if there are look cleats that come with an offset so that the foot can sit a few mm further out. Like a high Q factor cleat.

On time cleats it's easy because you just swap left and right to produce a Q-factor shift.

Are there such look cleats?

Not seen any cleats like that personally, but did you already do washers between the pedal spindle and crank? That'll buy you a couple MM. I've also swapped cleat washers or filed the stock washers in various ways to allow a little greater range of cleat adjustment than the stock setup permits. If you take a look at his cleats, you may find that there is one bit that is much more limiting of the adjustment range than the rest of the screw/washer/cleat complex.

On the higher Q option front, I think Shimano do long spindle versions of their pedals now, and that system is fairly similar to Look. Not to say that it's compatible, mind you, but just that for not much more than new Look cleats you can buy a whole Shimano setup. Having said that, I have not confirmed that the long spindle versions go for the same outlandishly low prices as the regular Shimano models.

[gramsqueen]

Bummer about the cranks man.

When this was happening to me my drive side crank was getting loose and I was throwing chains, another time was my front derailleur high limit was too far out and angular alignment was incorrect.

[alcatraz]

Good idea.

He's using vector2 pedals that have those pods with a cable reaching around the arm. Should be ok with maybe 2mm washers to start with.

We'll see.

I'll also try to force the cleats to the inside to produce maybe one more mm of clearance.

[alcatraz]

Bummer about the cranks man.

When this was happening to me my drive side crank was getting loose and I was throwing chains, another time was my front derailleur high limit was too far out and angular alignment was incorrect.

The cranks were scratched before I started working on the bike, plus they aren't exotic and hard to replace, so no biggie.

Thanks for the tip. Because he's running a compact I thought we can improve the fd/chainring clearance (minimize it) by using one of those 4degree angle correcting washers for the fd. That way the arch of the fd follows the chainring the whole way better. He did buy a set of 53/39 chainrings already so that might fix the fd position without any washer.

It's a big guy. 125kg that's been running marathons. When he puts the torque down the chain literally ejects unless it has enough teeth and tension.

He hasn't dialed in the pedal stroke yet. That and the fact that his legs are heavy he defaults to low cadence or standing up for acceleration. I think some one sided pedaling exercises will help to even out the power on the pedal strokes, up the cadence a tad and thus lower the torque.

What I don't understand is how those pro sprinters don't have chains flying all over the place.

This guy I'm helping has broken a few chains going up hills, even though he's somewhat new to cycling. I have never broken a chain.

[wheelbuilder]

The whole situation sounds like a disaster.