fixed wheel chain problem

big R

im sure someone on here knows the problem -

when i put the cranks on my fixed wheel to 12 0'clock the chain is tight, then when i move the cranks round to 6'oclock the chain is pritty loose :?:

is it because the rear sprocket is worn unevenly? its only a fairly cheep one and 22 tooth (put it on for a hill climb and left it on to improve my spinning ).

or is it because the chain is worn? 1 1/ 8

- sprocket and chain are about 5-6 month old and i do about 80-100 mile a week on it.

any help / explanation would be appreciated - cheers

Anonymous

Is your wheel sat in the dropouts correctly? This could make it sort of 'eccentric'. Either that or oyur bb is really won but you'd probably have noticed that.

varno

big R wrote:

im sure someone on here knows the problem -

when i put the cranks on my fixed wheel to 12 0'clock the chain is tight, then when i move the cranks round to 6'oclock the chain is pritty loose :?:

is it because the rear sprocket is worn unevenly? its only a fairly cheep one and 22 tooth (put it on for a hill climb and left it on to improve my spinning ).

or is it because the chain is worn? 1 1/ 8

- sprocket and chain are about 5-6 month old and i do about 80-100 mile a week on it.

any help / explanation would be appreciated - cheers

Probably because the chaig isnt round..TA are renowed for it... Get a Dura ace abd that fix it, other than that it could be the sprocket (not being round) or a bent crank axle.

Smokin Joe

I'd guess at uneven wear on the chain, which is not uncommon and well known to motorcyclists who do not have a derailler to even out the slack. Assuming none of the faults mentioned above apply you should set chain tension at it's tightest point.

big R

yep the wheel is correctly in the dropouts - and the bb dosnt feel worn , its only 6 month old as well (its a mich one so should be ok)

cranks arnt bent either

- its my commuting bike so i didnt realy (and carnt afford) to splash out on Dura Ace and top end stuff as the roads are full of holes and everything gets badly worn in the wet and winter grime of commuting

the chainset is a zenith RPM, the chain a miche 1 1/8 and the rear sprocket was one from SJS cycles as it was the largest i could get for the hill climbs i did.

thanks

pb21

90% sure its just the chainring.

Smokin Joe

pb21 wrote:

90% sure its just the chainring.

Well I'm 92% sure it's the chain. :evil:

Monty Dog

The fact that you've got a base-model chainset - probably with stamped rings and not machined ones is probably the reason. The chain goes tight because of variances in effective radius of the chainring teeth - compounded by inaccuracy of the chainring spider / bolts too. Try and find the highest point of the ring and adjust tension for that point.

Haynes

93% sure it the chainring.

There is usually some play in the chainring to get it more concentric. Loosen the bolts enough so it will slide around but not too loose and tap the chain ring where its tight. Im sure there was something on sheldon brown about the correct procedure. You can live with a bit of variation in chain tension but would obviously be a problem if its too tight on part of the revolution then so loose on the other that the chain would fly off. I find it just takes a bit of fiddling about to get it just so.

graham_g

Just to add that I agree with the above. I've had exactly the same problems before now and other than using TOP quality chainrings and sprockets, there is a little room for adjustment that gets things perfectly adequate for commuting duty! Sheldon's method got things more workable for me.

See the 'chain tension' paragraph at the bottom of this page:
http://sheldonbrown.com/fixed-conversion.html

"Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Spin the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.

This takes a little bit of your hands learning how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt.

Once you have the chainrings centered and secured, adjust the position of the rear axle to make the chain as nearly tight as possible without binding. Notice how freely the drive train turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible."

4candles

Stick some blu-tac on the chainstay and monitor the gap between it and the teeth on the chain ring.. this is what i did when i noticed it on my track bike, i also did this with the arms on the chainset and found that the arms either side of the crank were 1.5mm 'out' and the clearence to the frame was constant.. and that was on a Campag. Record track chainset ! :roll:

scherrit

Square chainrings from TA..... a fave of mine, too! The Sheldon trick of loosening the chainring bolts is a good one for minor out-of-round rings. Better quality rings and to a lesser extent, cogs make your life MUCH easier when setting up fixie chains....

You might possibly see if the spider is carrying the ring slightly off centre (less likely, tho') and move the ring around one chainring bolt position and see if it's better or worse?
Good luck!
S.

SDP

i would go with combo of c.ring & sprocket..one of them sounds bio pace!

get a good 3/32 ring & a decent 3/32 sprocket & run a 1/8 bmx chain on it ...

evens out a lot of intolerances ..

pete.whelan

If it is always tight at the same point when you turn the cranks, then 99% likely to be the chainring. If it goes tght at any other point, then look at the rear cog.

meagain

What the majority says! Ring most likely culprit: either not round or warped. Combination of sprocket and ring possible. Chain at fault only if very worn IMO.

big R

thanks for the help - i will have to have a proper look at it this weekend.