Poxy gears something is wrong

[Danthefestaman]

Im guessing that Carreras are not highly rated on here which I can understand. I rebuilt one years ago because it was the only reasonable local bike I could get. I made it my own replacing everything apart from the headset as off memory was a Carrera part.

My problem is I replaced the gear set with Shimano everything, Alivo front and rear derailleur, Alivo crank, Shimano shifters, Shimano HG cassette (HG-51-8CW), Shimano PC830 chain, Shimano bottom bracket and I cant get the gears to set right. The rear is fine but the front struggles to shift to the outer ring and when it does its very close to rubbing. Its especially difficult if your pedalling hard (going up hill). Ive already changed the bottom bracket to a new original Carrera item because I read the tapers on the bottom brackets held the crank arms to far apart. A little difference but still not 100%. Any body else had any trouble with the Shimano Alivo stuff? I know its the cheapest of the cheap but it should work ok. I've followed the park tools guide got the rear right but front not quite there. The only thing letting the bike down now which is a shame. I want to get it right so the wife can ride it and I will get a retro bike when I can source one.

 

[Paul R]

Hi there have you got the front mech close enough to the largest chainring it. the gap should be about 2mm between the outer large chainring and outer mech plate

 

[Danthefestaman]

Re:

Yep ive tried every possible way had it so close it was catching the middle ring. To get it to clear you would have to have the front forced right over and hold it there. I have the old Shimano bottom bracket so when I go to work I will pick up a file and try to add a couple of mm to the taper and see if it moves the crank in.

 

[legrandefromage]

dont file the taper down!!

Have you used the adjustment screws on the mech?

 

[lensmansteve]

dont file the taper down!!

Have you used the adjustment screws on the mech?

My first thought too. If the limit screws are out of adjustment, or the cable has any slack then you'll always struggle to get the big ring working. Don't blame the Alivio, budget Shimano works fine if it's set up well. As for filing the tapers, forget you ever thought of that. Bottom brackets are available in many lengths. Check that your middle ring lines up somewhere near the middle of the rear cluster and you won't be far adrift.

 

[Danthefestaman]

Re:

Good point about checking that the middle ring aligns with the middle of the rear. When on the inner cog on the rear and outer on the front the chain seem like it wants to drop down one gear. Seems to pull at an awful angle. Really odd I replaced like for like in the sense of 8 speed for 8 and so on. I think the original kit was SR suntour but the crank was worn out. Knowing the bike, mainly obviously frame was not worth a lot or desirable I chose to use budget Shimano to make it decent but at a cost and ive never been able to sort the front mech.

Also following the park tool video the b-screw adjustment on the rear mech seems to do bugger all. Sure I would have checked the chain length and size of gears e.t.c seems like there is no real slack in the chain someone better at bikes might tweak it but got to be close. On the plus side still rides !

 

[legrandefromage]

If you have changed the crank arms, it sounds like they sit too far out

 

[Danthefestaman]

Re:

I think that to. I'm going up to work today so will pick up a vice and a decent file and experiment. The bottom bracket only costs a tenner so no hassle. Either the top edges of the taper want a little tidying up or needs a slight re-profile.

 

[hamster]

DON'T FIDDLE WITH THE TAPERS. They are precision ground to (IIRC) 2 degrees. ANy misalignment and the crank will work loose, destroying the crank tapered socket in the process. It simply sounds like you have the wrong length bottom bracket. Check it in the Shimano tech docs or on Sheldon Brown. Probably it should be 113mm tip to tip.

 

[lensmansteve]

Re: Re:

I think that to. I'm going up to work today so will pick up a vice and a decent file and experiment. The bottom bracket only costs a tenner so no hassle. Either the top edges of the taper want a little tidying up or needs a slight re-profile.

You've had some very experienced bike engineers saying that filing the bb spindle can only end in tears.. Ignoring the near-impossibility of keeping the cranks spinning on plane, have you considered the amount of filing required to make a noticeable difference to the spindle length? Anyway, as Fleetwood Mac sang, you can go your own way.. All the best..