Do I need to replace it all???

tik33

HI there, newbie here - and sorry, it's a bit of a long post

I'm riding an old 2nd hand specialised (in London - so don't want to get a posh new bike) and it seems to be pretty good except that the chain keeps coming off. Which I found out can hurt when your bike falls over and you scrape your knee across the pavement.

So, took it into bike shop and they said that chain needs replacing - no probs - I can handle that.
However, not as simple as that, they said that I need to also replace the chainset, the cassette at the back and the derailleur - that would be more than the bike cost!

so, should I just bite the bullet and buy all those things - or try and get away with less.

do bike shops try and sell you stuff you don't need? could I just put a new chain on and see what happens???

so, assuming that they're right - I now need to buy the stuff (or is this a question for the gear forum?)

I've got a 7 * 3 speed gear shifter - not sure what make though (bike not with me at present) - should I get the most gear that I can find - or should I upgrade? I've had a look at wiggle - and budget items seem to be approx £70 for all of it. However, is it as simple as choosing any old 7 speed chain (eg Shimano HG40), 7 speed cassette (eg shimano HG30), chainset (shimano nexave T303) and deraiilleur (alvivio M410)?

Will these parts go together - will I suddenly find that I need to buy a bottom bracket or crank for a pedal or something? Do I need to look at the other bits on my bike - brand of shifter, etc? (I suppose this is the advantage of going to a LBS - but then you seem to pay quite a bit extra?)

Thanks all for your help.

ride_whenever

I'd make it into a singlespeed.

you'll need a chain, circa £10 (absolute rip off tops) sprocket £20 chainring £10 (cheap steel one ie deore will work fine) and to get the rear wheel respaced/redished £20 (labour) possibly a tensioner (use your old mech!)

This probably wont work out a lot cheaper, but that's due to the re-dishing of the rear wheel, once this is done you'll find it goes a lot further between drivetrain replacements as the chain isn't run diagonally.

tik33

Thanks for your reply and although tempting, I'm a lazy *** and I'm not sure that my poor old legs could cope with a single speed...

wgwarburton

Hi,
The chain wears and the effect is that the pitch (distance between links) increases. this is often called "stretch", though technically, that's not what actually happens.

This then causes secondary wear on the sprockets & chainrings. The teeth become distorted as the pressure on the load bearing faces takes its toll.

Typically, the problem shows up when the most-used sprockets and the least-used ones get sufficiently different that the chain won't run well on both. A new chain will run on unworn ones but not on the ones that have had heavy use.

In theory, you can change only the badly worn parts- the chain, the worn rear cogs and chainrings, however it may be difficult to get matching replacements. A new chain and freewheel is pretty much a requirement and a skeptical look at your chainrings should let you see if you need to replace one or all of them. If you have a road bike and rarely use the big ring it could well be fine. Similarly a road-ridden ATB may have a virtually untouched inner ring.
If you have an entry-level chainset with the chainrings rivetted on, then you'll probably have to replace the whole lot anyway.
The rollers on the rear mech might be noisy after the chain is changed- if this bothers you, or if they are actually bad enough to cause a problem then you should be able to get replacements.
In your shoes I would avoid going down the upgrade path (narrow chain, new mechs & shifters and more sprockets). IMHO more hassle than gain.

Cheers,
W.

tik33

W,

you've hid the nail on the head. Right, exactly what I was looking for - questions though:

1. rear mech - is that the derailleur? reading between the lines - are you suggesting that I should try without replacement and see how I get on?
2. If I want cheap n cheerful - where is best place to shop - wiggle, evans cycles, or independent lbs?

Thanks in advance

wgwarburton

1 Yes and yes.

2 Dunno, but if you go to your LBS and something doesn't fit you've a better chance of getting help.

If they are doing the work it's better value for them (and you) to minimise labour by replacing anything that night need it. The balance is different if you're doing the work and they should understand that.

Cheers,
W.

always_tyred

I'm a little surprised that the derailleur is supposed to need replacing. I'd guess that it would shift better with a new one (as would my bike), but it may very well be fine with the old one (as is my bike). Did they say why it might need replacing? The jockey wheels can be replaced quite easily, if they are worn. In the absence of a good reason, I think in the first instance you should try without replacing the rear mech.

Again, you have to try quite hard to wear out the chainrings. Definitely worth a shot without changing them. Even if they are worn, chances are that the middle will have been used a lot more than the others (it seems that some people go for years without using the confusing shifter on the left).

7 speed stuff isn't hard to get hold of. You would be able to get away with 8 speed chainrings anyway I think. Cheap and cheerful, if they have the bits, is Halfords.

Give another bike shop a try.

Oh, and £50 isn't that much - it might be more than the bike is worth, but if you go out and get another £75ish second hand bike, how must will you have to spend to make it suitable for daily commuting?

Also, drive trains wear out. I've had cars worth less than the price of 4 new tyres, but its still worth the new tyres because there is good chance that any other car will need them at some point in the near future anyway.

drewp2008

the pivots on the mech wear and it gets a bit of a wobble on, making shifting crap.

If they say it needs doing, it does. Maybe even chainrings too i might have thought.

Dont base repairs on the value of the bike either. Get it done properly and youll enjoy it much more

Vivid

If your chain comes off, it could well be that the derailleur is wrongly set up. The Stop Screws may need to be adjusted to stop the derailleur pushing the chain off.

always_tyred

drewp2008 wrote:

the pivots on the mech wear and it gets a bit of a wobble on, making shifting crap.

If they say it needs doing, it does. Maybe even chainrings too i might have thought.

Dont base repairs on the value of the bike either. Get it done properly and youll enjoy it much more

I would have thought that "crap" shifting was okay, providing that the chain was not dropping all the time.

In addition, just because a bit shop says so it most certainly does NOT follow that something needs doing, or cannot be done. If you ever get a stuck seatpost or a crank arm jammed on the spline, or a bb fused in the shell, you will soon learn that "you need a new one" is neither an acceptable first answer, nor the only one.

Sometimes they are right, but its always good to question.

tik33

thanks for all your thoughts

I'm a terrible cynic and always think that if someone can sell you something else - they will!

Halfords is a good idea - although probably good to actually take bike in and go to different lbs to make sure that all the bits 'work' together (my local halfords would mean driving...) and get second opinion...

tik33

just as an update - went into Evans cycles and they were very nice. I'd been on their website and had a list of things and prices of bits that they do - they don't keep the budget stuff in stock - but the guy said actually that in his opinion I might be able to get away with just replacing the chainset and the chain - leaving the cassette and the mech - or at least seeing how it goes...

Of course, he did say I might need to replace the bottom bracket....!

will now order the chainset from internet.

wgwarburton

tik33:

> will now order the chainset from internet.

From Evans, I hope? Otherwise they might not be around to offer advice next time...

Cheers,
W.