Chain ring assistance

[Threadingham]

Hi - new to forum and new to home mechanics so bear with me. I have an early stumpjumper m2 which I love. This bikes not the issue, the offending bike is a trek 6700 from I think around 2001. I bought it for £30 as parts but I can't bring myself to kill it (such a nice frame). So the chain/crank slips under pressure. I think it's the chain rings as they look terrible and the middle is buckled and will start with these. It has a bontrager comp crankset (4 bolt) square BB. I like the set so would like to keep if possible. Can I just replace rings, they are 44/32/22? If so any advice on this or recommendations on where to get rings, second hand looks like a lottery. Stu

 

[Markybeau]

Post a photo, let's have a look at the chain, rings and rear cassette.

It could be either one / or a combination of those three.

 

[Betsy]

So the chain/crank slips under pressure.

It sounds like your chainrings are knackered but what you're describing here^ can be caused by any number of things.. could just as likely be your cassette, you could replace your chainrings cheaply but that might be just the first step

edit- damn, marky beat me to it!

 

[bikeworkshop]

A lot of bikes sold cheap have badly worn chain and cassette.

Pull the chain away from the front sprocket (at the front, on the big ring)
If it comes 2/3 up the teeth, the chain is a goner.
Cassette wear is hard to identify, but if the chain is well worn, it will take the cassette out fast.

Middle rings have a lot of cuts and shaping when new to make the indexing work. People often think this is damage.

Compare the teeth parallel with the crank Arms (unloaded section) to perpendicular (heaviest load). If they look much different, the ring is toast.

Middle rings wear out the fastest.

Used ones are usually exactly that - don't bother.
New would be £15.
Some 104mm 4 arm cranks have a lip that interferes with a standard ring, but it can be ground off.
If you want to use the bike you probably need chain, cassette, middle ring - but you could try replacing the ring, then the chain, then the cassette to see if you get function.

 

[Betsy]

Check if there is play in the sprockets of your cassette, are any of those gears loose / can they be rotated slightly (clock/anticlock) ?

If yes, this probably isn't going to be that cheap'a fix.

 

[Threadingham]

HI all. Thanks for responses, wasn't expecting that..... so pics attached. One problem might be in eagerness with my £40 new toolkit started stripping back. Chain been taken off but looked knackered. Rear wheel/cassette looks pretty new and feels ok. Large ring awful but it slipped in middle. Also took shot of BB which I removed and cleaned up. No matter what I have to change those rings. Cheers stu

 

[wiredfool]

Rings and cassette look pretty worn. Inner chainring might be alright, as sometimes they’re the only steel ones in the set.

 

[Markybeau]

Cassette - sprockets 5-8 look heavily worn to me. If you start with the largest cog - that's generally how they all should look, but as you move down they have progressively sharper teeth. They should be 'blades' rather than 'points'.

Middle and outer ring on chainset need replacing. Granny ring looks OK.

 

[Threadingham]

Thanks again. Can see what you are saying a out the cassette, think the bikes been hammered. Can't believe anyone could even ride it. So I want to do a nice job with this bike but need to not spend more than £100. Is it doable for rings, chain and cassette? Any suppliers recommened. I will attempt to do it all. Cheers stu

 

[bikeworkshop]

Also the bb isn't threaded in fully
You need chain, cassette, mid and large ring.
Perhaps you can borrow the bb tool.
Total around £60 - support your lbs