Chain/Crank Binding Problem

[autolycus]

It felt as if the bike was slipping under load in the two smallest rear cogs. And after several frustrating hours adjusting and indexing front and rear derailleurs, i think i've nailed the problem. With the chain on the inner crank, the outer edge seems to be catching 4 rivets around the outer crank. Once the lower gears are selected on the rear, the chain runs inboard enough to clear the rivets. These rivets seem to be doing absolutely nothing, except providing something for the chain to snag on in the highest gears.

Assuming i have found the problem, can anyone tell me the solution, please?

Thanks.

 

[derrick]

A photo might help.

 

[Yellow Saddle]

It felt as if the bike was slipping under load in the two smallest rear cogs. And after several frustrating hours adjusting and indexing front and rear derailleurs, i think i've nailed the problem. With the chain on the inner crank, the outer edge seems to be catching 4 rivets around the outer crank. Once the lower gears are selected on the rear, the chain runs inboard enough to clear the rivets. These rivets seem to be doing absolutely nothing, except providing something for the chain to snag on in the highest gears.

Assuming i have found the problem, can anyone tell me the solution, please?

Thanks.

You haven't nailed the problem yet. Those rivets you mention are there to help the chain climb from the smaller to the larger chainring. Yes, they can catch the chain when cross-chaining as you describe, but no amount of adjustment will make it go away. You should simply not cross-chain.

The slipping under load is a different problem, probably due to a worn chain on a good sprocket, but you haven't given us enough info to diagnose that problem.

 

[raleighnut]

It is due to 'cross chaining, this pic might help explain how to avoid it (BTW they are duplicate gears when you do it and are not needed when riding)

 

[gbb]

The cross chaining may be the issue, but its not the only possible cause...
Does it slip consistently/regularly...does it do it under heavy load only or at all times,,,
If its when you really press hard on the pedals, any gear, it could be the freehub is sticking.
You'd kinda sense a sudden loss of connection, a slip but no real noise, then pressure would come back as normal,
Freehub slippage in my experience tends to only happen occasionally, but always under load.
Its hard to seperate out what is the cause, slipping chain, usually because of worn components or your freehub,

 

[autolycus]

Thanks very much for the replies, but i'm struggling a bit to understand.
Yellow Saddle - you say i should simply not cross chain, but i'm not sure what you mean. Do you mean i should not use the smallest 2 cogs with the smaller crank? I've had a bike with a similar groupset before and was able to use any of the 20 gears with no such problems. And i'm not sure the gears are actually slipping, it just felt like it when under load. But the chain may be a bit knackered - it seems to move around laterally quite a bit. I'll have another look tomorrow.

Edit gbb - the symptoms you mention are rather like the issue i'm having and the bike has been very little used for a while. Could i service the freehub? How?

 

[Yellow Saddle]

.
Its hard to seperate out what is the cause, slipping chain, usually because of worn components or your freehub,

It is easy to separate the causes. Freehub failure will happen in any gear given enough force on the pedals. Chain skating on a worn sprocket will only happen on a very narrow range of sprockets. Visibly both are difficult to see as it happens but if you mark the chain's position on a sprocket with black ink on both the chain and corresponding sprocket tooth, chain skate shows up immediately as a shift in position. Freehub slip won't show a change in chain and sprocket relationship.
Further, just about 100% of the time a failure in a pawl-actuated freehub will present as sudden loss of engagement and stay disengaged until a bump or vibration returns the pawl. However, DT Swiss clutch actuated freehubs will fail just like a worn sprocket - only under pressure. When pressure is released, the clutch engages again.

 

[Yellow Saddle]

Thanks very much for the replies, but i'm struggling a bit to understand.
Yellow Saddle - you say i should simply not cross chain, but i'm not sure what you mean. Do you mean i should not use the smallest 2 cogs with the smaller crank? I've had a bike with a similar groupset before and was able to use any of the 20 gears with no such problems. And i'm not sure the gears are actually slipping, it just felt like it when under load. But the chain may be a bit knackered - it seems to move around laterally quite a bit. I'll have another look tomorrow.

Edit gbb - the symptoms you mention are rather like the issue i'm having and the bike has been very little used for a while. Could i service the freehub? How?

Yes, cross-chaining is a mechanical crime punishable by malfunction. Don't do it. Yes, you had other bikes that didn't do it but they had a different chainline (see the excellent drawing above) or the chainstay was longer, which relaxes the chain angle and gives a bit of clearance. This problem has absolutely nothing to do with chain wear. Under tension the chain is straight, no matter how much or little it is worn.

I suggest you look up cross-chaining and learn some new habits. Cross-chaining dramatically decreases component life. The fact that the bike allows you to do it doesn't make it mechanically sound. If you look up the manuals for Shimano, Campag and SRAM, they'll all have a diagram showing a cross-chained drivetrain like in the sketch above, with a large cross through it. That cross speaks all languages, including bicyclese.

 

[gbb]

It is easy to separate the causes. Freehub failure will happen in any gear given enough force on the pedals. Chain skating on a worn sprocket will only happen on a very narrow range of sprockets. Visibly both are difficult to see as it happens but if you mark the chain's position on a sprocket with black ink on both the chain and corresponding sprocket tooth, chain skate shows up immediately as a shift in position. Freehub slip won't show a change in chain and sprocket relationship.
Further, just about 100% of the time a failure in a pawl-actuated freehub will present as sudden loss of engagement and stay disengaged until a bump or vibration returns the pawl. However, DT Swiss clutch actuated freehubs will fail just like a worn sprocket - only under pressure. When pressure is released, the clutch engages again.

We agree...
I did say....


'If its when you really press hard on the pedals, any gear, it could be the freehub is sticking.'

Interesting to see your analysis of slippage as in marking the sprockets and chain. One to remember.

 

[Ajax Bay]

It felt as if the bike was slipping under load in the two smallest rear cogs.

Now that you've nearly sorted it, OP, do you get any malfunction when in the large chainwheel and either of the smallest two sprockets, ie when putting power through them eg as a hill kicks up from level and you've haven't changed down?

Interesting to see your analysis of slippage as in marking the sprockets and chain

Careful, @gbb , @Yellow Saddle 's text describes recording of skating, not analysis of slippage.

 

[autolycus]

Just to be clear, i don't tend to cross-chain when riding. I use the large chainring 95% of the time and just drop to the smaller one for the lowest gears when i need them. It's just that i've adjusted the derailleurs on five different bikes in the last couple of years - double and triple chainsets - and this is the first time i have not been able to run smoothly through every combination of gears on the stand. Which is the reason i assumed that something - other than my riding style(!) - needed fixing. Interestingly, i think this bike has the longest chainstay of the lot.

Anyway, i'm learning all the time and grateful for the knowledge shared by those who kindly replied. It's a newly-purchased (secondhand) bike that i've barely ridden so i was rather looking to find fault. It seems the fault was with the fixer not the machinery.

EDIT: Ajax Bay - I'll just check the symptoms again tomorrow in case i've misconceived the problem, because i have a feeling it might have 'slipped' on the large chainring before i did the adjustments. I will report back after further analysis.

 

[Ajax Bay]

50-34 compact chainset, right?

 

[autolycus]

Close Ajax Bay - it's actually 48/34 with an 11/36 cassette; the bike is a 2012 or 2013 Sirrus Comp. Not sure of the exact 'model' or if it's a compact - or indeed what a compact is exactly.

I spent another frustrating hour today doing the front derailleur yet again and there is actually a problem setting the h adjustment. If i screw all the way in, and back off 1/2 turn i get a clearance of barely 1mm at the tightest point. However, there seems to be several mm clearance at other points along the chain. With this setting i get a scraping sort of sound on every revolution on the stand and what resembles a loud croaking noise under load each revolution on the road. I've tried various settings, but it seems to me that it's either rubbing on the inner edge of the derailleur or the outer depending on how far in the adjuster is screwed. And the noise happens in all gears only on the large crank.

As long as i keep out of the two highest gears on the cassette, the small crank works perfectly, so clearly my earlier diagnosis was a red herring.

 

[Ajax Bay]

OP, do you get any malfunction when in the large chainwheel and either of the smallest two sprockets?

 

[autolycus]

I get a noise in every gear when on the large chainwheel - the apparent slipping seems to have disappeared after my work on the derailleurs. There is a loud croaking noise under load and a graunchy click when not under load. And it happens on every revolution of the pedals. I am suspicious of the large chainwheel itself, but there is no obvious (to me) buckling or other damage. As i say, the bike runs as smoothly as anything on the small chainwheel (except in the highest two sprockets, which i'm pretty sure is cross-chaining as diagnosed above).