Suntour Chainset

[Nebulous]

I have an Edinburgh bike cyclocross bike, which is in need of some care and attention. It has a square taper bottom bracket. I changed the chain today and the BB revolves very freely, but there is a fair bit of movement in the chain on the front ring- almost catching the mech on both sides in some gears. It is a Suntour SR XCT triple.

I'm wondering:-

a) what is going on here? Could the chainrings be bent, or perhaps more worryingly, could it not be square on the taper?

b) what should I do about it? I've never worked on a square taper bracket before. Should I buy a new chainset and replace it? I use it pretty much every day for a very short commute and don't want to have it off the road if I can help it.

 

[screenman]

Going by what you have wrote have you thought about an lbs?

 

[Nebulous]

Going by what you have wrote have you thought about an lbs?

It does look like that from my post doesn't it? I use Edinburgh bike for bikes and lots of bits, but do all my work myself. I've a decent toolset, a bike stand and maintained an Allez on my own through 12,000 miles and 3 or 4 new hollowtech brackets. I'm back to work tomorrow, thought my bike needed nothing more than a new chain and left that until the last minute, so I've taken a real wobble here. I'd probably rather replace both the chainset and the BB than take it elsewhere, but I was hoping someone would say just hit it with a hammer and it'll be fine!

 

[screenman]

To be honest the bit where you could not tell if it was bent or not led me to give that advice.

I am sorry for having read the post wrong.

 

[Leaway2]

If it has come loose on the taper, you can just tighten the screw. You do need a very thin socket though. More likely it is bent. To get it off the taper is easy, but you do need the special tool. When I bent mine after hitting a kerb as I came off, I replaced the ring (from Spa cycles). It is a Tiagra double. I guess you have nothing you loose by banging it flat.

 

[screenman]

If it has come loose on the taper, you can just tighten the screw. You do need a very thin socket though. More likely it is bent. To get it off the taper is easy, but you do need the special tool. When I bent mine after hitting a kerb as I came off, I replaced the ring (from Spa cycles). It is a Tiagra double. I guess you have nothing you loose by banging it flat.

It may not be bent.

 

[Leaway2]

What about putting a block behind the NDS and tapping the DS with a mallet to see if it will sit down on the taper.

 

[Sharky]

If you remove the chain and rotate the chainwheel can you see lateral movement on the ring? Thos will eliminate the chain as a cause of the problem.

Check if the chainring bolts are all tight and not missing.

Good luck

 

[mjr]

Check it's not bent by looking across it with the chain on another ring.

Have you done the centre bolt up to 40Nm torque? It might not be seated square.

 

[Ajax Bay]

there is a fair bit of movement in the chain on the front ring

Could you clarify what you mean, please? Are you saying that as you turn the cranks, the (top of the) chain ring moves from side to side? Does this happen on the small ring too?
Provided you have a crankpuller (which are not expensive) you can easily take the crank off the square taper, give it a clean up and reseat it (I say with a thin film of grease, others say dry). That should eliminate the seating as the cause, or when you take it off you can see what's happened. Chain rings are pretty robust and are unlikely to have been bent without a substantial bash - of which you'd be aware.

 

[Nebulous]

Okay folks - update on this, sorry for not returning to it sooner.

What I meant was that the ring was moving with reference to the chain guide on the front mech as I turned the pedals. There was about 3 mm of movement, alway at a specific point. I can't recall anything which would have caused damage, but I did come off quite spectacularly on ice about a year ago and I had a bad chain jam when changing gear about 3 weeks before changing the chain.

Anyway last week after changing the chain the front changing was fine, but I had problems with one of the rear gears skipping. I'd obviously left the chain too long before changing it. I don't use many of the rear gears, but switch regularly from middle to large ring at the front. Having a look at the rear block I decided there was a bit of play in the rear mech, so I ordered a rear mech and a new cassette online.

They both arrived on Friday, so I set out to change them yesterday. I still wasn't happy with the front chainset, so I pulled the taper (surprisingly easy, I had a tool already) I nipped out and bought a new chainset and replaced it as well.

Everything is running well on the stand, my journey to work today will be the real test.

I now have a new rear mech, new cassette and new chainset for about the price of a cassette on my best bike, which largely gathers dust.

 

[DaveReading]

I have an Edinburgh Bicycle tourer with a Suntour crank and triple chainwheel.

Coincidentally (or not) I've been having problems recently adjusting the FD, which I put down to a slightly out-of-true middle ring. Not as much runout as yours, maybe a mm or two, perhaps scope for a judicious whack with my plastic mallet ?