Derailleur tuning question

[LeakySeals]

My apartment complex had 30+ abandoned bikes attached to the garage bike rack. The land lord got fed up and after several warnings tossed most of them. I dumpster dived a brand new "Timberline ltd Triple Triangle" that only needed a quick release thingy for the front tire. Took that off another bike. I adjusted everything, shifts good. But I cant understand why the chain hits the frame when I coast. I fooled with the "b-screw" (I think thats what its called). It seems to create tension on the Derailleur as it extends. But whether its loose or tight the chain still hits the frame. The chain is brand new. But could it be too long? do I need to lube something? Another noob question. The front tire spins forever if I turn it. But the back one with the ticking sprocket slows down fast, as if it needs lube or somethings too tight. Should the rear wheel with sprocket spin as freely as the front?

 

[javacontour]

Sounds like it's in the rear hub. The wheel should freewheel, but sounds like it is turning the gear set, which is causing the chain to hit the frame.

What happens if instead of coasting, you take you feet off the pedals? Do the pedals still turn?

I don't think this is a derailleur issue, but a rear hub issue.

But it's been 100 years since I seriously messed with the mechanicals of bikes. I just ride them now, so others might want to chime in.

 

[scurvy]

Derailleur tuning is a bit of an art. To get started you should only need to adjust the limit screws so that it doesn't overshift the chain into the spokes when going into the biggest cog or off the cassette when going to the smallest. Usually with those set correctly, the only other thing to frob is the cable stretch barrel adjuster at the shifter housing.

Sometimes they need an overall gross adjustment by hand. Usually only when you've crashed the bike hard enough to bend the linkages is that necessary.

Are you sure you're in the correct set of front rings for the rear cogs? I.e., if the chain is hitting the frame because it's "too long", make sure you're not cross-chaining by being on the small ring and small cog at the same time.

The chain could be too long... but if it's the chain what came on the bike it's probably the right length. If indeed it is too long it's fairly trivial to remove a couple links with a chain tool.

The rear wheel should coast nearly as freely as the front, with only a light ticking from the freewheel mechanism. Sounds like you may need to dumpster dive a couple more bikes for parts!

 

[LeakySeals]

Here it is.. was barely used.


Derailleur and sprocket.


Here is where its hitting. Thats M1 HM 5w30 on the frame. Used that to lube the chain.

 

[scurvy]

Correct me if I'm wrong, but it looks like you're on the big front ring and the second-to-largest rear cog. That's not a good combination for chain or derailleur life... and only one poorly adjusted derailleur shift away from the bad combo of biggest ring & cog.

As far as the chain slap it's not uncommon to have a little in that area; all my mountain bikes always did. That's why there's a decal on the chainstay in that spot!

 

[LeakySeals]

Yeah, I was trying different combinations to see when the chain would hit and why. I just took a dive and pulled out 2 other bikes. They don't do that. And the back wheel moves more freely. Not sure if there is a connection between the two issues. is it ok if I try some silicon spray around the sprocket and Derailleur parts?

 

[scurvy]

Go nuts with the spray, but be warned most of it will just drip right off. The overwhelming majority of rear hubs have been sealed for years.

But if there's another one with the same number of cogs on the cassette and same size wheel, just swap the entire wheel over. The vast majority of 26" 'mountain bike' rear wheels are freely interchangeable. Quick release skewers and brake caliper unloaders make it quick & easy.

 

[cchase]

Set chain length by going into the big ring up front and the big cog in the back and making the derailleur cage lay flat out. That's the gear combo that requires the longest chain, so it should never need to be any longer than that. Out of the box, chains are longer than you would need on that bike so just taking it out of the box and attaching it will most likely result in a chain that's too long.

As far as the wheel slowing down, it's possible the hub bearing preload is too high, or it could be something as simple as a dragging brake. However, if the chain is hitting the chainstay when you coast, I'm thinking that the entire problem may be caused by some issue with the freewheel. A quick and dirty fix in that case would be to take some light penetrating oil and spraying it into the freewheel with the rear wheel off the bike and laying flat on the ground, then taking the freewheel and manually getting it to spin. It should spin relatively easily, but not "coast" down to a stop. Think of a well greased ratcheting action. If it's bound up from corrosion it may be difficult to manually ratchet - in which case it's also the likely source for the chain hitting the chainstay and the wheel not spinning.

 

[LeakySeals]

I have some Kano Aerokroil. Will take the wheel off and spray up into the freewheel and see what that does.

 

[javacontour]

As I said above, it makes since. If the free wheel isn't free, then it will keep "pushing" the chain, if the crank is stationary.

It would also act as a brake when you spin the back wheel, which is how the OP described the behavior of the wheel when he spun it.

 

[nthach]

lower-end hubs and all Shimano hubs use cup and cone hubs, a 13-17mm cone wrench and a 13-17mm open-end does quick work of taking them apart. However, lower-end bikes will use cassette freewheels with the ratcheting mechanism integrated into the cassette, while mid-higher end use freehubs.

I'd check the chain length - wrap the chain on the big cog-big ring combo. Pull the chain so the derailleur is extended but not overly stretched. You want to have a 2-link overlap at the end of the chain loop. Instead of reusing a rivet, go to a bike shop and grab a SRAM PowerLink. It will make life easier.

More here: http://sheldonbrown.com/derailer-adjustment.html#chain

Once the chain is back on the bike, you'll need to adjust the front and rear derailleur travel limits, set the B-tension so it is a certain distance away from one of the cogs, and play with the cable tension.

 

[cjcride]

Chain slap, it's quite common, not a problem. Spray the thin oil all around, just keep it off the brake shoes, rims and tires.
Ride Safe.