chain coming off crank while reversing the pedal

[Wheel]

So I had another thought based on how you described the action of the chain compared to another bike when backpedaling. If the freehub/freewheel on the back wheel is stiff, even a slightly mis-aligned chainring(front sprocket) or slightly bent tooth will make the chain jump off.

If you pull the rear wheel, the cogs there should spin in reverse pretty easily with a ratcheting sound. If it's stiff, the freehub (if it's that type) needs some work, and a very light grease. If it's a freewheel, I wouldn't take it apart, but soak it in penetrating oil to see if that helps.

This may be more a job for a bike shop, and it may not be worthwhile on a Huffy.

 

[Vikas]

I do not have a bike repair stand (looks like opportunity tp purchase yet another tool!). So all the testing is confined to having the side stand down. This means I am limited in terms of the crank movement. BUT the important point is the same tooth and same crank position causes the chain to start coming off which indirectly indicts that particular tooth.

 

[BRZED]

Vikas, your chain rings are not Biopace, are they?

 

[Vikas]

I do not recall any such sticker on the bike. It is Huffy Cross Sport 12 speed featuring "Grip Shift"; here is the ladies bike which we retired when wife bought the Specialized.

http://nh.craigslist.org/bik/5039805913.html

 

[BRZED]

If it were Biopace, you could tell by the ovoid shape of the chainrings. I thought that maybe Biopace might be more prone to chain, tooth and alignment issues, although this is merely speculation.

 

[javacontour]

I missed the pants getting caught in the front derailleur the first read through.

Compare the alignment of the front derailleur in the parts bike to that of the suspect bike.

Perhaps the front derailleur is bent in such a fashion that it is taking the chain off when pedaling backwards.

It just may be a combination of all the above. You have a sketchy tooth in the front chainring, a bent derailleur and perhaps some components that need a good clean and lube such as the jockey wheels and rear freewheel assembly.

Most of it is stuff needed to tune up a bike anyway. If you need a front derailleur, you have a donor on the other bike.

Likewise with the crank. If the cranks are the same, you could likely swap the wobbly crank with the bent tooth with the crank from the donor bike.

 

[Vikas]

I am not sure if I know what I am seeing but the chain stays smack in the middle of the front derailleur guide and does not make contact either in forward or backward pedal motion. That is why I think it has to be either single bad teeth (fix with a pliers or the out of plane crank (fix with a pry bar

Derailleur is the thingy which forces the chain to move from one chain ring to another, correct? So it should touch the chain only during shifting, correct? Once shift is completed chain and derailleur should keep their distance from each other, correct?

 

[javacontour]

Originally Posted By: Vikas
I am not sure if I know what I am seeing but the chain stays smack in the middle of the front derailleur guide and does not make contact either in forward or backward pedal motion. That is why I think it has to be either single bad teeth (fix with a pliers or the out of plane crank (fix with a pry bar

Derailleur is the thingy which forces the chain to move from one chain ring to another, correct? So it should touch the chain only during shifting, correct? Once shift is completed chain and derailleur should keep their distance from each other, correct?


That's right, the Derailleur is the mechanism that guides the chain from chain ring to chain ring in front.

If it doesn't touch the chain when pedaled in either direction, then it's not a likely suspect.

I'm still interested if the chain goes slack when you pedal backwards.

If you really think it's out of plane or there is a bad tooth, why not just swap the mechanism with that of your wife's old bike, assuming it will fit?

The other question is does it do it regardless which cog is selected in the rear? I.E if you have the chain on the big cog on the rear is it more or less likely to drop the chain than when on the small cog in the rear?

 

[Vikas]

Quote:
The other question is does it do it regardless which cog is selected in the rear? I.E if you have the chain on the big cog on the rear is it more or less likely to drop the chain than when on the small cog in the rear?
Yes, it does it on at least few gears in the back. I did not bother checking the end gears to avoid crossing the chain.

But I do see that the slack in the chain increases while going backward which implies things are not as free as they should be.

I do not know how to swap the crank (or the chainring) from one bike to another. They are identical though.

 

[javacontour]

Probably a one-piece bottom bracket:

Quote:


One-Piece Bottom Bracket
Remove the left pedal by turning it clockwise with a 15 mm wrench.

Remove the lock-ring on the left side with a hooked lock-ring wrench and lift off the keyed washer. Unscrew the bearing race. The bearing race has groves in it that allow you to turn it using a flat head screwdriver.

Take the bearing race out of the left side of the bottom bracket housing. Partially remove the one-piece crank through the right side and then reach in and remove the right side bearing race. Slide the rest of the crank out of the bottom bracket housing.

Clean the bearing race, lock nut, keyed washer and crank with cleaning solvent and a cloth. Clean and grease the bottom bracket housing and discard the old bearings. Remember to grease the new bearing cages and the bearing race.

Put a new bearing cage on the right side of the crank (rounded side facing outward) and reinsert the crank through the right side of the bottom bracket housing.

Put the left side bearing cage around the crank with the rounded side facing outwardly. Attach the left side bearing race and tighten it by turning it counter-clockwise. Push the keyed washer back into place. Add the lock-ring and tighten it. Wipe off any excess grease and put the left pedal back on.



Read more : http://www.ehow.com/how_7514314_replace-crank-bearings-huffy.html

 

[Vikas]

Thanks! That seems within my capabilities!!

 

[Vikas]

Java,

Your youtube link told me what to try. I compared play in the crank and realized that my bike had the play which was not there in the spare bike. I removed the outside bolt as shown in the video. After taking off the washer, it became obvious that inside locking ring was loose. I loosen it lot further until I could get some spray grease in there and then tightened it until the play was not there. I also realized that the outside nut needs to have the proper preload. I tightened it first and then slowly backed it off until the pedal was no longer binding.

Now with no play in the crank, the chain stays on even when pedal is rotated backwards. So this is fixed.

Now I realize how stupid idea was to bend the teeth by locking pliers or bend the chain ring by pry bar :-( Being able to compare against the other identical bike and your link to the video were instrumental in avoiding a big mishap.

More maintenance is now planned for. I will start new topic or use the existing one for chain cleaning.

If you are ever in the Boston Metrowest area, I owe you a beer or two!

 

[Vikas]

aaarg; the offer is withdrawn :-( still tries to jump off at the same point; now pliers or pry bar has to come out

 

[Vikas]

OK, finally! I had to use pliers on one tooth. Looks like, it is now fixed. By the way, I used my own homemade ingenious bike hanging system. I should have taken a photo. Think garage door angle bracket and a ratcheting strap and you will get the idea. Not exactly a sturdy stand but more like a third hand holding the rear of the bike up!

I cleaned the chain using the fancy made in italy three brush gizmo and put semi-dry chain lube from a dropper bottle. Hopefully, my chain issues should now in the past. Thanks for all of you.

 

[javacontour]

You are welcome. oilBabe and I will visit Boston in the fall, FWIW.

Bike happy!