wobbly bottom bracket & slipping chain

[pompeygazza]

Greetings,

1st post so be gentle. My chain has started to slip when I put pressure on the pedals, also whilst investigating this I have noticed that my crank is a bit wobbly. I have tried to tighten the crank (cotterless) using a socket but it appears to be fully tightened and is still wobbly.

The chain seems to have a gap between it and the gear, is this normal?

Hope you can help.

pompeygazza

 

[fossyant]

Your bottom bracket may need replacing - certainly sounds like it (it's the bearing in the frame) and skipping gears is a sign of worn chain and the gears on the wheel (freewheel or freehub cassette).

What's your technical knowledge like ?

 

[pompeygazza]

technical knowledge not bad, don't have a puller though

i'll ask a former colleague if he's got one.

does the chain sit snug i.e. no gap underneath, on the crank gear? i ask because it looks like only 4 or 5 teeth are taking all of the torque!

cheers

 

[fossyant]

If your crank gears (chainrings) look like shark's teeth, then yep - you'll need new ones as well. The reason the chain isn't sitting correctly is that it's worn out - explains the skipping.

If you can borrow tools, then so much the better.

You'll need a crank puller, and bottom bracket tools - now do you know what type of BB it is - i.e. does it have a lock nut on the left side, or does it have a splined inner edge that's inside the 'shell'

Worth having a look at sheldonbrown.com, or parktools.com for some ideas about what you have.

What's the bike, how old, and how ridden is it ?

 

[pompeygazza]

splined inner edge that's inside the 'shell'

bikes about 5 years old, ridden 15 miles a weekday for the last 2 years.

cheers

 

[montage]

what fossy said

(thought I would keep this thread bumped, as on the front page, next to know how, this thread appears as "wobbly bottom")

 

[levad]

I have just had the exact similar problem!

Had the bike 9 months and done just over 3,000 miles. Changing gear wasn't working properly so I tried re-indexing, no good. Got myself a new chain and that helped a lot. While I was replacing the chain I found that the cranks wobbled side to side, that would explain the 'clunking' sound I got every so often and possibly the chain skip in top gear.

Anyway, I have just finished replacing the bottom bracket (a Shimano 4500 cup unit) and replaced both gear cables for Gore RideOn cables.

I was a bit daunted so read Sheldons information, looked at Shimanos WEB site for component instructions and read the info on Park Tools site. All very good and I now have a quiet machine that seems to change gears much better.

Mondays commute will tell me whether everything is really OK.

The correct tools, patience and taking a bit of time appears to have done the trick.

 

[alecstilleyedye]

my wife's bike had a wobbly bb, turned out that just the l/h side cup needed tightening. although it looked like a cartridge bb (had the splined cup fitting), it was actually a cup and cone affair.

 

[Sittingduck]

Can you post a close-up picture of this:
"no gap underneath, on the crank gear? i ask because it looks like only 4 or 5 teeth are taking all of the torque"?


SD

 

[Radius]

Do the gaps look something like this? If so, then what fossyant said is correct.

 

[pompeygazza]

many thanks for all of your replies. i have attached pictures of how the chain sits. doesn't look right to me.

thanks again.

pompeygazza

 

[Radius]

Yep, the chain is very very stretched and you can see the teeth are worn. Unfortunately you'll probably have to replace the chainring andmost likely the casette as well as the chain looking at that...

 

[Landslide]

Riveted chainrings - you'll need to replace the entire chainset.
So, new:

• Chainset
• Chain
• Cassette
• Bottom bracket

Looks like a lot, but you have got 5 years of use out of the last lot...

 

[pompeygazza]

many thanks for all your replies

sounds like an excuse for a new bike to me ;0)