cujik

Hirst time post a newbie biker so will try to explain best way i can, Having problems putting chain on my new mountain bike " 27 sp" Chain is either to tight " cant get it into front and rear large gears at the same time " or if i lenghten the chain the cahin becomes too slack and rubs against its self on the rear drailier" also when i back pedal the chain skips from the biggest gear on the back to the smaller ones. any advice much appreciated..

bikinfool

You shouldn't cross chain (using large chainring with largest cog and smallest chainring with smallest cog), but your chain should be of a length to allow the large/large combo in case you accidentally shift into it. You might read up on chain sizing and rear derailleur adjustment at parktool.com in their repair section...

operator

https://www.parktool.com/repair/readhowto.asp?id=26

Learn how to properly select chain size. If you're using a chain without a masterlink, you cannot repin that chain. Or you risk chain failure.

cujik

The chain i am using is a sram chain with power link!!

DannoXYZ 

Don't back-pedal. Unless you have a rear-derailleur on top of the cluster as well as on the bottom, there's nothing to prevent the bent chainline from pulling the chain sideways and towards the centre of the cluster.

wmodavis

Back peddling is not a proper way to test chain length, chain tension or just about anything related to your bike except that it's operating normally. When peddling backwards (for whatever reason) there is nothing to guide the chain to stay on the chosen cog as there is when you pedal the useful direction. That is one of the derailer functions - to guide and hold the chain on the chosen gear. But it cannot do that when peddling backwards. If you are in a front/rear gear combination which has the chain at an angle rather than straight and true with the chainring/cog combination there are side forces attempting to pull the chain sideways and there is nothing other than the teeth engaging the chain to counteract that force. Often in this case the side forces win. Make a Halloween resolution to not pedal backwards and if you inadvertently slip into your old ways and the chain, on its own, goes to an un-chosen cog, at least remember that you can avoid this embarrassing and maddening phenomenon by peddling forward. And that has the advantage of propelling the bicycle forward.

operator

It's pedaling people. Jesus h christ.

cujik

OK, have fitted the chain as per instructions on the park tool website and all seems ok. I' ve noticed that when i am on both small gears that the chain hangs on the frame oof the bike when theres nio tension but i guess this would not happen if i didnt use the gear set up when out on the bike!! Thanks again all!!

Al1943

Chain's too long.

cujik

I dont think the chain can be too long because if i take out another link i cannot get the chain into both big cogs and chain has no bend in it around the drailier!!

Ashen

There is no reasonable condition where you would want to be on both big cogs. It just doesn't make sense. You would never do this.

aljohn

With modern bikes I suppose I have to agree with Ashen. But I look back with fondness to my 10 speed, with double chainrings and 5 cogs. I selected my moderate touring range of gears carefully and I could use any of the 10 gears with no problem! With a 10 cassette, triple rings, short chainstays you do not have a realistic 30 gears. How many useable gears are possible with this setup? I am curious.

Mr. Underbridge

I could see it happening in two circumstances: 1) you forgot what chainring you were in. 2) Short uphill where you end up in big/big briefly.

Or put another way - I don't feel sufficiently capable in my abilities to stay out of big/big to risk ripping the drivetrain apart if I accidentally do it. In any event, having a chain long enough to wrap the big/big combo won't be a reason for the bike to behave badly.

Al1943

OK, my mistake, you do need to be able to shift into big to big combination without maxing out the derailleur just in case you hit that combination accidentally. Do you have a mountain type long cage derailleur. It sounds like your cage may not be long enough.

DannoXYZ 

What's the teeth-count on your chainrings and rear sprockets?

cujik

Not sure exactly what you guys mean with those last two questions, can you describe in basic terms and if need be i will go to my bike and get counting, Yes this is a mountain bike and has the drailier set that came with it, I have seen the same sram on the same bike in the shop too.

exRunner

What is this thing exactly? I have a Trek 820 with a 48/38/28 by 13/34 and it will not go on the 48-34 combination (I tried it last night just for this thread). On that bike the 34 is disproprotionally larger than the 6th gear (a 28). It will however shift to the 48-28 just fine with only a very slight amount of cross-chaining chatter.

For the "it makes no sense" crowd for Big-Big, it does if you are racing and need to quickly shift up going over the top. In that case not having to shift the front makes a big diffence to getting back on the power coming down. (Yes some of us actually pedal hard on down hills)

Ashen

I'd be very surprised if the OP was racing.

Bianchigirll 

as Dr CamBell used to say "then don't do that"!! LOL

exRunner

Your original statement was not qualified, it was generalized. You don't get to change gears now.

bkaapcke

Get the chain on the biggest cogs, front and rear. The cross chaining position. Reset your low limit screw to move the der cage so the jockey wheel is aligned right under the large cog. Then turn the screw another half turn to move the jockey wheel towards the spokes. This will cure the problem for the large rear cog. Should help the rest, too.

To make sure the extra half turn isn't too much, on the stand, shift 3-2-1 on the cogs several times. You want to make sure the chain doesn't jump into the spokes. bk

1901

Had similar problem. Chain slipping when backpedaling. It was the chain; it was made of a very weak metal and was too flexible sideways.

Was able to pedal forward. The derailleurs were keeping the chain in place, but when tried to pedal backward the chain slipped from both chain-ring and freewheel. It didn't happen on all speeds. Just for the sprockets that were not aligned with the chain-ring. Out of 7 speeds/sprockets, I was able to pedal backwards on only 3 of them (on speeds 3-4-5).

Tried to get used to it and use the bike as is, but the chain broke in about 100m; at the first stop (I suppose the chain is most stressed when you stop) Changed with another identical chain and it also broke in 100m. Those bad chains costed me less than 1€ each. Changed with a better chain made of strong steel and less flexible sideways that costed 3€ and I no longer have any problem pedaling backward.

cobba

Cross chaining:

https://www.youtube.com/watch?v=yDPc1WqT2PE

https://www.youtube.com/watch?v=nzSUaPYZsMw



Cross chaining = a bent chain line

A bent chain line + back pedalling = a chain jumping/skipping off the gears

A straight chain line + back pedalling = a chain staying on the gears