Notchy feeling turning cranks

philak

With my bike on a stand i have noticed there is resistance to turning the cranks by hand. I feel a distinct notchiness as i turn them. The real wheel freewheels very well on the stand and if i remove the chain from the front rings the cranks turn smoothly with little resistance so it seems its either chain or rear cassette.
i've re-oiled the chain and checked for tight links but since the feeling is constant and regular im guessing its not one or two bad links anyway. I would say the notch feeling co-incides with either the rollers or sprockets engaging /disengaging with the chain but i can't see any obvious interference or misalignment. On the road changing is crisp and clean but i'm obviously putting energy into turning the cranks that is wasted. I don't get this problem on my MTB which feels smooth to turn the cranks by hand.
Although ive fitted different wheels to the originals the chain and sprockets are the originals and have done about 800 miles im guessing so i can't think its wear either.
In case it's relevant the bike is a Giant SCR ltd with Tiagra throughout.

Any thoughts anyone?

onbike 1939

I take it the chain-line will be fine as you haven't had the chainset and BB out. I would check from the rear of the bike that the Tension pulley is directly under the Guide pulley on the Rear Deralieur. If this is not in line then you would experience the notchy feeling you describe. This, in my opinion tends to be the usual reason for this symptom, in that the Rear Der is vulnerable to knocks.

philak

Thanks, i will have another look at it tomorrow and let you know the outcome.

alfablue

The guide pulley could be too close to the cassette, then it will go "notchy" as the chain, pulley and cassette sprocket are all running together - its a long shot as you would only probably get it on the largest sprocket. To fix it, adjust the B screw

philak

Just had a quick look. The guide pulley isn't too close to the cassette but it does appear, as onbike said, that the tension pulley is slightly out of line with the guide pulley as though the cage has been twisted slightly. It's only very slight but enough to see with the naked eye.
I'll have a go at straightening it tomorrow. Thanks for the replies guys.

Bronzie

philak wrote:

I'll have a go at straightening it tomorrow. Thanks for the replies guys.

Be very careful how you go about this - if you have an aluminium or carbon frame, the rear mech will be screwed into a hanger which is screwed into the frame - this is designed to break if the rear mech suffers a sideways knock (rather than damaging the frame). If you are not very careful, you will simply snap the hanger and you will then have to find a replacement which can be a problem on older frames.

Suggest you look at replacing the rear mech first if this has become damaged/distorted - if it's not this, ask your local bike shop to check the rear mech hanger for alignment.

If however, you have a steel frame, you will probably not have a rear mech hanger and can probably straighten it by hand - again take great care not to snap it off though!

philak

Well i've looked at it until my eyes glazed over . Had a go at tweaking the cage gently into line but i'm not even sure anymore whether it was out in the first place.( I do still have the same notchy feeling though so i guess it will be down to my LBS at the weekend.

Am i right in saying that the Tiagra kit won't have bearings in the pulleys that could need attention?

Thx

onbike 1939

philak wrote:

Well i've looked at it until my eyes glazed over . Had a go at tweaking the cage gently into line but i'm not even sure anymore whether it was out in the first place.( I do still have the same notchy feeling though so i guess it will be down to my LBS at the weekend.

Am i right in saying that the Tiagra kit won't have bearings in the pulleys that could need attention?

Thx

I can't see the bearings in the pulleys being the cause. More likely that the chain is being pushed off-line somehow. Try turning the pedals while moving the tension pulley slightly inwards and outwards and see if the notchy feeling disapears.