Chain and sprocket replacement

Discussion in 'Cars, Bikes 'n AFVs' started by theblindking, Jan 28, 2012.

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  1. All,

    What is the logic behind changing sprockets with a new bike chain? The only thing I can think of is something to do with "bedding in" and a new chain may somehow cause damage to the teeth of old sprockets but it sounds unlikely.

    Basically is it really neccesary or another manufacturer con?


  2. Know bugger all about two wheel stuff but on classic cars when fitting a new timing chain I do fit new sprockets as chain and sprockets have worn together and older blokes with beards told me to. If they are cheap why not? They are going to last ages.
    P.s. on timing chains a new tensioner goes on as well for me.
  3. That's a new one on me, back in the 70s and 80s I'd change the sprockets if the old ones were looking worn, although most chain suppliers would offer chain and sprockets as a package at a cheaper all in price.

    Nowadays with modern chain tecnology I wouldn't like to say. Most of my bikes have been shaft driven. It is a source of wonder to me that bikes still use chains; imagine the scene at Ferrari or Porsche;

    'Boss I've designed a new 200mph sports car!'
    'Excellent Chef, show me the pans... why the **** has it got a chain final drive? Go away and come back with a shaft driven beastie!'
  4. Sprockets are cheap, chains are expensive.
    A worn sprocket will wear a chain faster. Good sprockets will extend the chain life a bit.
  5. You only really need to change if the new chain is skipping on the sprocket or rear cassette. The chain stretches over time. Well, actually it doesn't. The rollers in the links wear (through mud and grit) which makes the chain longer and this wears the teeth of the sprocket or cassette. A new chain might not be compatible with the worn sprocket, thus skipping.
  6. Cheers All.
  7. Ive arrived late to the party but:

    You can get away with not doing it - for a while - say every second chain but its a false economy as a worn sprocket may reduce the life of the new chain and relatively speaking chains are the expensive part(and eventually the sprocket will wear out completely).

    I have seen some horrific looking sprockets on tight-arse rat-bikers' bikes. Eventually the teeth of the sprocket wear to sharp points then start to bend over and finally the chain just doesnt catch at all. Only once have I known someone get to quite that point.

    Best tip - buy a shaft or belt drive bike and leave the 19th century behind you. Even Harleys use belt drive! For some bikes you can retro-fit a belt drive. It would probably be the best move you could make.
  8. Belts are the way forward. I've got an old Motor Cyclists book somewhere that says so. It points out that chains are metal and will wear very quickly. Somewhere I've also got a small tool for removing/ replacing leather links.
    I've had a quick look, can't find it at the mo', it was printed pre nineteen canteen. Must be in a shed.
  9. Check the feel of the new chain in the sprocket teeth, if it's a bit slack or the teeth are starting to become hooked, then it's new sprockets I'm afraid. If the links of the chain are snug in the teeth, then leave it until next time.

    Unless of course you're thinking of 120mph+ frequently and the thought of a jumped chain at that speed terrifies you (it used to do me), in which case play safe.
  10. A lot of this thinking relates in a different way to certain types of bike.

    If you have an off-road machine like a trials bike or a green-laner then you will get away with replacing those components in what ever order suits you with no problems.

    Once you start involving motocross bikes,road bikes and especially sports bikes then you are really going against good advice if you do not replace the components as a set. As stated before, the chain is the expensive part of the kit and the sprockets often cost as little as 15% of the chain.

    The chain will wear and develop " tight spots " that really means it articulates badly at a certain point, with road biased bikes this constant juddering is taken up by the rubber mountings in the cush drive and will also translate into a specific wear pattern in the sprockets...getting more pronounced as the chain stretches.If you fit a new chain onto old sprockets, you are not getting an effective fit between components....the chain is not sitting perfectly between the teeth and can move around on the sprocket. This simply means that your new chain is going to wear, far faster than a normally maintained one would and you are having to replace them more do not save money in the long run.

    Just for interest.

    I used a single set of chain and sprockets on a trans-Australia trip ( on a Suzuki DR650 ) and only needed to replace them on the last week of the trip...after 35,000km they were still good because of constantly maintaining the chain and keeping the correct tension.

    I have also retired my shaft driven BMW ( BMW R100GSPD )and gone back to using a chain driven BMW ( BMW G650GS ) because a well looked after chain can last a long time, you can see what is wearing and how, it can be repaired ( spare Links ) .....and is a shitload easier to get hold of and fit than a complete shaft drive in the middle of nowhere ( as I found out )
  11. Just for infor the machine is an Aprilia RS 250 with no pervcievable wear on the sprockets but the chain has staretched to the extent that it's shitting me up.

    Thanks for all the good advice - I have to agree with Baboon though; chains are easy to repair on the fly.
  12. Erm........arriving fashionably late. If I may throw in my 2 cents worth:

    From an 'engineering' perspective (I'm not a engineer), just had a few bikes in my time. I used to change out chain and sprockets as a set, something to do with a worn sprocket is not nearly as well defined as a worn chain. Do not run new chain on worn out sprockets because it can cause the chain to wear rapidly. The pitch of the new chain is much shorter than the effective pitch of the worn sprocket, so the total chain load is concentrated on the final sprocket tooth before disengagement - understand that my fine feathered friends?

    Then, when the chain disengages from the sprocket the roller is jerked out of the hooked portion of the sprocket tooth and the results in a shock load on the chain as the load is transferred from one tooth to the next...........breath out.

    ****, listen to me sound like I know what I'm talking about.
  13. To add to the argument, it is well known that softer materials eat away at harder ones?? Phosphour bronze wheels would remain intact and the harder mild steel covers would be eaten away at the anchor points.

    From my windsurfing days, people got all uppity at putting taught nylon straps on a board, a few hundred miles on the road and the board would go airbourne, the soft board had chewed through the strap, not vice versa.
  14. BC, you may be right but I couldnt quite tell what you were trying to describe as relates tothe question at hand!

    BB, you sound like you know what you are talking about because, apparently, you do!

    Baboon, is, of course, correct that it does depend what you are doing with your bike which final drive system suits best. Chains, though requiring the most maintenance are the easiest to work on. They are also technically simpler than a shaft drive and, as stated, easier to "bodge fix" if you are in that situation. I am not certain but I would also imagine that on average a chain drive would be lighter than a shaft drive although, with clever design, maybe not by much (the shaft drive unit can be incorporated as a structural element of the swing arm, clearly a chain cannot!).

    A modern belt drive is lighter than a chain, lasts longer in normal road use, doesnt stretch and needs no servicing. Belt drive is also quieter and smoother than chain. They can be expensive to replace but they will work out cheaper due to long replacement intervals. The weakness of belt drive is that it is unsuitable for off-road use as the belt can be easily damaged by grit etc lodging between the belt and pulley. If a belt does go, it is likely to be sudden and total failure due to damage not wear!

    But the simple answer is still - "Best practice" is to replace chain and sprockets as a set
  15. Good advice, mush.

    Just to add my two-penneth to the thread. The chain can be replaced without the sprockets but its hardly worth it in my experience (over 30 years, Jap, Brit, Yank and Italian machines). As an interim measure, if you're strapped for cash and the sprockets aren't excessively worn, changing the chain without the sprockets is ok so long as you keep a close eye on the sprockets from then on. Some chains can be bought 'off-the-roll' and work well for this job. However, I've found over the years that doing this can lead to losing a tooth - easy enough to see on the rear but not so on the front. This can make your chain slip off and lock your back wheel. Not too bad a low speed (which has happened to me) but I dread to think what it would be like if you were motoring along. Also, it never quite works out as a 2:1 ratio. For example, putting the new chain on the old sprockets increases the wear on the sprocket as they are (these days) often made from a soft alloy. So, you will need to change out the sprockets before the new chain is fully worn. I would never put an old chain on new sprockets. I always change both chain and sprockets at the same time. Buying the whole lot as a kit works better in my opinion and is more cost effective over the long term.

    A quick tip...

    As chains wear they become slack not just front to back but also side to side which increases the wear on the sprockets, so it's important to keep your chain properly adjusted and lubricated (where appropriate). As Mush says the sprockets will appear hooked through excessive wear (particularly if you're a bit heavy handed with the throttle, wheelies, fast starts, etc.) but I would say that, if your sprockets are hooked at all, they're past it because the new chain just won't sit right - again, as Mush says above. A seized link can also cause the chain to jump off so make sure you roll the chain through a couple of complete revolutions (on and off the stand) after fitting or adjusting and don't over-tighten.

    And on chain vs belt vs shaft...

    Belts are good because they require less routine maintenance but replacing them is a nause as the swing arm needs to come off and they are expensive. Shafts work well as long as they're kept well lubricated but if one fails, it's going to cost you. Great on a tourer but they never quite deliver the grunt that chains and belts do. I replaced the belt on my Harley with a chain because it's more versatile in my book and I ride every day so it works out more economical. It gives me more wheel options too, is easier for a road-side repair, and replacement is easier to fund when cash is short. The draw back being it takes more routine maintenance but I check my chain every few days and I've been doing it this way for so long that it only takes a few minutes to adjust.