Chain jumping off ring on hard accel; suggestions?

Werehatrack said:

miles, previous two owners apparently knew zip about maintenance and adjustments; after fixing
multiple minor probs and getting the wheels straight, it rode pretty well, but recently developed
a bad habit.

On hard pedalling when using the big ring, the chain will suddenly leap off the teeth and sit in
the gap between the ring and the crank guard.

New chain? Sounds like the teeth on the chainring are worn out by an old chain. If you replaced the
chain, it can easily cause this just like the chain can skip on the cog.

--

David L. Johnson

__o | "What am I on? I'm on my bike, six hours a day, busting my ass. _`\(,_ | What are you on?"
--Lance Armstrong (_)/ (_) |

David L. Johnson' may have said:

Werehatrack said:

miles, previous two owners apparently knew zip about maintenance and adjustments; after fixing
multiple minor probs and getting the wheels straight, it rode pretty well, but recently developed
a bad habit.

On hard pedalling when using the big ring, the chain will suddenly leap off the teeth and sit in
the gap between the ring and the crank guard.

New chain? Sounds like the teeth on the chainring are worn out by an old chain. If you replaced the
chain, it can easily cause this just like the chain can skip on the cog.

Hmmm. I'll take a look at the chain and the rings more closely. The chain didn't appear to be in bad
shape (no kinks, no obvious sloppy spots) but I didn't look really close at the teeth. I haven't
changed any components yet, so the stuff that's present is whatever the prior owners had (or hadn't)
put on the bike. It would not surprise me if the chain had been replaced and the ring left with
whatever warts it had.

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Werehatrack said:

David L. Johnson' may have said:

Werehatrack said:

miles, previous two owners apparently knew zip about maintenance and adjustments; after fixing
multiple minor probs and getting the wheels straight, it rode pretty well, but recently developed
a bad habit.

On hard pedalling when using the big ring, the chain will suddenly leap off the teeth and sit in
the gap between the ring and the crank guard.

New chain? Sounds like the teeth on the chainring are worn out by an old chain. If you replaced
the chain, it can easily cause this just like the chain can skip on the cog.

Hmmm. I'll take a look at the chain and the rings more closely. The chain didn't appear to be in
bad shape (no kinks, no obvious sloppy spots) but I didn't look really close at the teeth. I
haven't changed any components yet, so the stuff that's present is whatever the prior owners had
(or hadn't) put on the bike. It would not surprise me if the chain had been replaced and the ring
left with whatever warts it had.

They don't always LOOK worn. I've had the same experience (new chain, worn big CR causing this to
happen). While you're checking, also look for bent teath.

David

David Kunz may have said:

They don't always LOOK worn. I've had the same experience (new chain, worn big CR causing this to
happen). While you're checking, also look for bent teath.

On close inspection, the big ring shows some wear but not a tremendous amount; the chain sits all
the way into the sprocket even under moderate static tension. If this were a piece of industrial
equipment, I would not expect a problem from the wear. But what I also found was that when I put
weight on the crank, I get a significant amount of deflection off true in the assembly, and the big
ring has a pair of places where 5 teeth in a row have excessively trimmed teeth. I've seen a little
bit of tooth height reduction to aid in shifting on rings before, but by comparison to the other
three bikes, these are trimmed *a lot*. Added to this, the ring is apparently not all that well
hardened; I can see some spots on various teeth where the chain has chewed up one side of the tooth
and left it burred. I now think that what I'm seeing here is a combination of effects; deflection
under load on a poorly excuted ring that's not in the best of condition, which adds up to a leaping
chain under high strain.

I guess it's time to look for a stiffer crank and bearing assembly.

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Werehatrack said:

On close inspection, the big ring shows some wear but not a tremendous amount; the chain sits all
the way into the sprocket even under moderate static tension. If this were a piece of industrial
equipment, I would not expect a problem from the wear. But what I also found was that when I put
weight on the crank, I get a significant amount of deflection off true in the assembly,

What is "significant"? Any crank will deflect some. The question is how much is a problem.

Quoted message said:

and the big ring has a pair of places where 5 teeth in a row have excessively trimmed teeth.

That is commonly a design feature to allow easier shifting.

I've seen a little bit of tooth height reduction to

Quoted message said:

aid in shifting on rings before, but by comparison to the other three bikes, these are trimmed
*a lot*.

That varies with brand and model.

Quoted message said:

Added to this, the ring is apparently not all that well hardened; I can see some spots on various
teeth where the chain has chewed up one side of the tooth and left it burred.

How hard do you think you can make aluminum? Chains are steel. They are much harder. This is normal
(well, depending on how severe it is).

--

David L. Johnson

__o | Some people used to claim that, if enough monkeys sat in front _`\(,_ | of enough
typewriters and typed long enough, eventually one of (_)/ (_) | them would reproduce the
collected works of Shakespeare. The internet has proven this not to be the case.

David L. Johnson' may have said:

Werehatrack said:

On close inspection, the big ring shows some wear but not a tremendous amount; the chain sits all
the way into the sprocket even under moderate static tension. If this were a piece of industrial
equipment, I would not expect a problem from the wear. But what I also found was that when I put
weight on the crank, I get a significant amount of deflection off true in the assembly,

What is "significant"? Any crank will deflect some. The question is how much is a problem.

I can get about 6mm at the teeth of the chain ring with the bike motionless and with me standing on
the pedals. Worse, however, I've noticed that the chain ring assembly apparently is only attached to
the crank arm at the hanger shaft; what looked like a spider was actually just a decorative plastic
cover, and the riveted chain ring assembly doesn't contact the crank arm anywhere except around the
shaft. I get the funny feeling that if I could see what was happening to that thing under load, I
wouldn't have to wonder why the chain was leaping. I still may yank the crank arm off and look at
the taper to see if it's wallowed, though.

Quoted message said:

Quoted message said:

and the big ring has a pair of places where 5 teeth in a row have excessively trimmed teeth.

That is commonly a design feature to allow easier shifting.

Two teeth shaved I've seen a lot, three teeth sometimes, but five shaved to less than half height?
That seems a bit much. It's obvious that the teeth were made that way, though, so it *shouldn't* be
a problem...but then, if the problem I have wasn't present, I wouldn't be looking for a cause.

Quoted message said:

I've seen a little bit of tooth height reduction to

Quoted message said:

aid in shifting on rings before, but by comparison to the other three bikes, these are trimmed
*a lot*.

That varies with brand and model.

Noted; the others here have two or three teeth that are shorter than the rest, but this is the only
one that has five clipped...and they're all clipped to the same height, no graduation as is the case
for the others, and they're clipped a lot farther than any of the others.

Quoted message said:

Quoted message said:

Added to this, the ring is apparently not all that well hardened; I can see some spots on various
teeth where the chain has chewed up one side of the tooth and left it burred.

How hard do you think you can make aluminum? Chains are steel. They are much harder. This is normal
(well, depending on how severe it is).

This isn't aluminum, it's steel (loosely speaking), and I've worked with aluminum that was harder
than this stamping. The burred face is away from the crank arm, and I have to wonder if the ridges
are picking up the link and walking the chain over the ring, or if they were formed *because* the
chain was walking over the teeth.. I can't tell if this is due to the jumping, or if it's
contributing to it.

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Quoted message said:

Quoted message said:

Added to this, the ring is apparently not all that well hardened; I can see some spots on
various teeth where the chain has chewed up one side of the tooth and left it burred.

We had this problem once with a strong sprinter--turns out that one chain link was twisted (twisted
sideplates) from shifting under power. Moral, inspect the chain link-by-link for free flex and
straightness, before deciding that the chainring is the problem.

Leave your front derailleur on and change your manager!

"Doug Milliken" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Quoted message said:

Quoted message said:

Added to this, the ring is apparently not all that well hardened; I can see some spots on
various teeth where the chain has chewed up one side of the tooth and left it burred.

We had this problem once with a strong sprinter--turns out that one chain link was twisted
(twisted sideplates) from shifting under power. Moral, inspect the chain link-by-link for free
flex and straightness, before deciding that the chainring is the problem.

Doug Milliken may have said:

Quoted message said:

Quoted message said:

Added to this, the ring is apparently not all that well hardened; I can see some spots on
various teeth where the chain has chewed up one side of the tooth and left it burred.

We had this problem once with a strong sprinter--turns out that one chain link was twisted (twisted
sideplates) from shifting under power. Moral, inspect the chain link-by-link for free flex and
straightness, before deciding that the chainring is the problem.

One more thing to get a closer look at, then. I didn't see any obvious probs on the first slow pass,
but everything's worth checking before stripping pieces off.

---
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Yes, I have a killfile. If I don't respond to something, it's also possible that I'm busy.

Have your DS fired!

"Doug Milliken" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Quoted message said:

Quoted message said:

Added to this, the ring is apparently not all that well hardened; I can see some spots on
various teeth where the chain has chewed up one side of the tooth and left it burred.

We had this problem once with a strong sprinter--turns out that one chain link was twisted
(twisted sideplates) from shifting under power. Moral, inspect the chain link-by-link for free
flex and straightness, before deciding that the chainring is the problem.