Tightening my chain (GN250) for the first time! [Archive]

sam.la

11th December 2011, 18:28

After seeing my chain I decided I should tighten it. I read the manual and it says 25-35mm sag at the middle of the front and back sprockets.

I am having trouble determining what this sag means? Does this mean it should be able to move up and down of a displacement of 25-35mm or how far is should be pulled down in rest position?

At the moment. I can only pull the chain down about 10mm but i can lift it upwards quite a significant amount I would say at least 7cm+.

I have also read in other threads the chain should be able to move about an inch so 2cm ish both directions? As mentioned above my chain will only go down a small amount? Does this mean I do not need to tighten?

Hopefully I made sense and I can get some good feedback :).

unstuck

11th December 2011, 18:41

sam.la

11th December 2011, 18:50

Yes. I've watched that video.

So to clarify the sag is the how much it can move up and down?

unstuck

11th December 2011, 18:54

Yep.:niceone:

sam.la

11th December 2011, 18:55

ok my chain needs a massive tighten :no:

cheers for that.

unstuck

11th December 2011, 19:01

http://www.dansmc.com/rearchain.htm If you are more of a reader.:headbang:

sam.la

11th December 2011, 21:12

Is the chain supposed to be uniformly tight around the full circumference? I think I have a tight and loose spots where the chain is more loose in small area and tight in another small area? :no:

Latte

11th December 2011, 21:35

Is the chain supposed to be uniformly tight around the full circumference? I think I have a tight and loose spots where the chain is more loose in small area and tight in another small area? :no:

Find the tightest spot in the chain, then adjust the slack so this point is at the correct measurement. This is a good sign your chain (and probably sprockets) are on their way out. Personally I would keep using them till the teeth on the sprocket are absolutely stuffed (bending over slightly) - but this is not recomended, be careful.

I may also have a rear sprocket on the "wall of shame" at dpc, one of the worst they'd ever seen, missing teeth, sideways bends. I definitely do NOT recommend using them that long.

F5 Dave

12th December 2011, 16:17

sadly they often get stuffed links, maybe as a result of sitting tightly curled around the front sprocket when left parked for months. If the chain tightens appreciably in any area or you can see zig-zagged links the chain is toast. They won't loosen up. Go ahead try, its depressing.

Running it too tight esp with tight spots will hammer the output bearing.

I always try a new bike by getting someone to sit on it while I check adjustment. Some bikes tighten appreciably with load so it is worth factoring in.

The Pastor

12th December 2011, 16:29

After seeing my chain I decided I should tighten it. I read the manual and it says 25-35mm sag at the middle of the front and back sprockets.

I am having trouble determining what this sag means? Does this mean it should be able to move up and down of a displacement of 25-35mm or how far is should be pulled down in rest position?

At the moment. I can only pull the chain down about 10mm but i can lift it upwards quite a significant amount I would say at least 7cm+.

I have also read in other threads the chain should be able to move about an inch so 2cm ish both directions? As mentioned above my chain will only go down a small amount? Does this mean I do not need to tighten?

Hopefully I made sense and I can get some good feedback :).

mate why do you not just give me a txt lol

The Pastor

12th December 2011, 16:34

your chain will be poked, you can get another chain from cycletards cheaply enough. You can get away with the cheap shitty chains, you dont need an o or x ring chain. (the high quality ones are waaay more expensive).

you might need to replace the sprockets at the same time. (most likely)

You do need to keep the chain tightened, having a loose chain wears out the sprockets and chain really quick.

You do need to keep the chain clean and oiled - oil it about once every 300ks. (once a fortnight or every 2nd tank etc)

bring it around to my place and we can sort it out.

The Pastor

12th December 2011, 16:42

you want 25-35mm slack. which is actually quite a bit. I'd go with 35mm going too tight on ur shitty bike would be a disaster.

http://www.scribd.com/doc/45216426/GN250-Manual