chain coming off crank while reversing the pedal

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I can see the bite mark on the tooth which causes the chain to start coming off. Fortunately this happens only when the crank is rotated backwards. Visually, I do not see anything wrong with the tooth. The entire crank wheel seems to be in one plane. The crank has four small screws. I am not sure but they must be the one holding the plastic cover. If I removed that cover, I will be able to get a pliers on the tooth but I really don't see it is bent or anything like that. I do notice some play in the crank itself. Mind you, this is a "classic" Huffy, 25 year old, US made, department store bike but I can raid parts from the other one which we retired after purchasing a "real" bike for my wife. Two gears on the front and this happens on the bigger diameter wheel. The rear gear does not matter as far chain slippage is concerned.
 
I would look for a bent tooth on a chain ring or a bent chain link and I would check alignment between chain ring and cassette.
 
Don't pedal backwards. Why would you?

Real bikes have special teeth that are made to help the chain move off the chainring or sprocket. Maybe Huffys do too. You didn't mention what gear you're in out back when this happens. If you're in one of the bigger gears it's not unusual.

Don't pedal backwards. Seriously.
 
Originally Posted By: AZjeff
Don't pedal backwards. Why would you?

Real bikes have special teeth that are made to help the chain move off the chainring or sprocket. Maybe Huffys do too. You didn't mention what gear you're in out back when this happens. If you're in one of the bigger gears it's not unusual.

Don't pedal backwards. Seriously.



Special teeth?

My specialized doesn't have any special teeth. It's a rock hopper. I had it custom made in Canmore. The crank was shimano. 3 on the front,9 on the back with thumb shift. Great bike.
Nthe crank was shaped like an oval which creates a flat spot that aids in derailment.
So no special teeth,special shaped crank.
My shifters could grab 4 gears at once. It was top of the line in its day. I bought top notch accessories.
Great parts.
 
Originally Posted By: AZjeff
Don't pedal backwards. Why would you?.


I pedal backwards all the time to align the crank arms horizontally when I have to clear a considerable obstruction in my path..
 
Originally Posted By: Clevy
Special teeth?

My specialized doesn't have any special teeth.


I think he is alluding to the design of the chain ring teeth, which makes the chain want to move up to the next chain ring. This makes shifting up easier.
 
Originally Posted By: BRZED


I pedal backwards all the time to align the crank arms horizontally when I have to clear a considerable obstruction in my path..


Most likely 1/4 to 1/2 rotation. Then a big bunny hop? I doubt that's what the OP is describing!
 
Originally Posted By: BRZED
I would look for a bent tooth on a chain ring or a bent chain link and I would check alignment between chain ring and cassette.



^^^^
this, or the play in the bottom bracket, or the frame itself is bent.
Something is out of line chainwise. You could check with a straightedge. Even 'special' teeth should be in the same plane, they are usually just ground differently to aid shifting.
 
It is NOT the chain because it happens at exactly the same point in the crank position regardless of the chain link location and only on the bigger front spoke. The rear spoke does not matter. The most logical explanation is that the tooth is indeed bent or the entire front spoke is wheel no longer planer (aka has become wavy) or crank bearing has too much play. But visually I can not see any evidence of the first two. I do see there is some play in the crank bearing but that will not explain why the chain will start to come off at exactly the same crank position. The play in the crank will affect both the bigger and smaller front spokes and also its effect would be mostly random to the crank position.

This thing started when my cuffs of pants got jammed in the chain during riding and the entire front derailleur cable came off. I put it back together to best of my ability and got the both front gears working after fiddling with it for a while. I mean if a highschool dropout kid can tune a bike, surely a post graduate engineer should be able to fix his own bike, right?? :)

The only time I need to rotate the crank in reverse is when either getting on the bike or loading it in the car.

Are those small screws for the cover, right? Why do you take it off? Doesn't that prevent the chain from coming off completely and literally falling down if it were to slip on the outside? Given the choice of chain getting jammed between the spoke and the cover or falling it off completely, I would much rather have jammed chain!

I will take pictures and post it later. Also I need to get my terminology correct as I might be describing the things right way! All I know is front has two wheels with teeth and rear has six wheels with teeth and there is a chain and some kind of laterally movable guide at both ends which allows chain to move from one wheel to another aka gears.
 
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There are derailleur travel limiter screws, high and low. Play with the low one until your chain can't come off. Probably it doesn't take much play in the crank to make it hard to shift down to the small front ring, having the limiter adjusted so it can't come off at all.
For the price of a decent bike though, I'd jack up the water bottle holder and replace the rest, before messing around with the huffy too much.
 
Yes, now when I compare my Huffy to wife's Specialized every time I load and unload them from the van, the differences become night and day! That one rotates backward like hot knife in butter vs mine which is more like dragging a sled on the beach! By the way, water bottle holders are off different types too. But the saving grace is that I was able to jam the old bottle on the new holder.

As I have said repeatedly, it not the limiter screws as this happens on that particular teeth and also I can shift the gears fine. I believe I am making right decision to leave the limiter screws alone. The question is should I attempt to bend that teeth even though I don't visually see anything wrong per se? Trying to get it to rotate backwards, I don't want it to start slipping while going forward!!
 
Originally Posted By: AZjeff
Originally Posted By: BRZED


I pedal backwards all the time to align the crank arms horizontally when I have to clear a considerable obstruction in my path..


Most likely 1/4 to 1/2 rotation. Then a big bunny hop? I doubt that's what the OP is describing!


It's still pedaling backwards. As for pedaling backwards for seversal full rotations, no, I don't do that, but I also don't think it causes the chain to hop if everything is properly adjusted and in good working order.
 
Originally Posted By: Vikas
Also I need to get my terminology correct as I might be describing the things right way! All I know is front has two wheels with teeth and rear has six wheels with teeth and there is a chain and some kind of laterally movable guide at both ends which allows chain to move from one wheel to another aka gears.


The sprocket-wheels ( not gear wheels, since they don't mesh with another wheel) on the front are called the chainrings, which are attached to a spider for easy removal. The sprocket-wheels on the rear are called sprockets or cogsets and come as a set either as what's called a cassette or a freewheel, depending on the design. All the sprockets, involved in shifting are also called derailleur gears (although they should be called derailleur sprockets, since gears mesh with each other, while sprockets are chain-driven) Shifting is accomplished with the front and rear derailleurs, which move the chain from one sprocket to another. I hope I got that right!
 
The question is why does the chain not fall off when pedaling forward, but only when pedaling backwards? The sprocket-to-derailleur angle doesn't change, but the tension on the top of the sprocket is higher when pedaling forward. The higher tension could prevent the chain from hopping off even if something like a chain link, a tooth or a derailleur is misaligned. How far do you have to pedal back before the chain comes off? If I can pedal back 180° without issues, I would just live with it.
 
As soon as the pedal is on one particular location which happens to be when the left pedal just crosses the lowest point. I can see that tooth riding on the chain link rather than hole inside the chain
 
Is the chain going slack on the top when you pedal in reverse?

It's possible the issue is with the rear derailleur and/or the freewheel mechanism in the rear wheel causing the chain to go slack when you pedal in reverse.

Make sure the freewheel and the jockey wheels on the derailleur are properly lubed and working.
 
It sounds to me like some kind of misalignment. The lower chain tension when pedaling backwards then causes the chain to fall off. The best source regarding bikes I know is the late Sheldon Brown. Maybe read his information on derailleur function and adjustment and take another close look at your bike's drivetrain.
 
Could be a bent tooth on the sprocket. If so an adjustable wrench clamped on the tooth can act as a pry to straighten it.

Sheldon Browns site is great for cycling stuff.
 
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