SS Chain tension.

andyrr
andyrr Posts: 1,822
edited February 2012 in Workshop
This might be something that is common but more noticable with a SS setup than gears :
when I check the chain tension on my Trek SS, to allow a reasonable allow of slack at the tightest, measuring at mid-point, the slackest point of the revolution is then quite a bit more. Haven't measured it but if, say, I adjussted it to have the slackest to be about right then at it's tightest the chain is almost complketely tight. Something in the transmisison is therefore not running 100% true - I'm guessing it is the BB/crank, it's running the originals here (12 months regular-use in) so replacement might be on the cards but I just think it's a bit crappy that I can't have a nice consistent chain tension.

Comments

  • Monty Dog
    Monty Dog Posts: 20,614
    Probably the chainring is not true and may be compounded by the crank / mounting bolts. Try slackening off the chainring bolts a touch and turn the cranks to see if it evens-out and then re-tighten? Try remounting the chainring at a few positions too? Quality machined chainrings are way more accurate that pressed ones. I aim for a bout 1cm of vertical 'play' in the chain at the mid point - any tighter and it tends to be noisier / less smooth.
    Make mine an Italian, with Campagnolo on the side..
  • andyrr
    andyrr Posts: 1,822
    Cheers, good suggestions there.
    Prior to this biek I'd never ruin SS so chain tension wasn't an issue really.
    Not all that long after I started using it the chain actually came off when riding and the end result was it jumped into the hub-side and chewed a couple of spokes. That would be with insufficient tension. I'm wondering if I sometimes run a little too much as tension as I'm now on my 3rd freewheel (all Shimano ones) as the bearings go rough as hell after a time and too tight a chain would excerbate this. More even tension would give the drivetrain an easier time of it.
  • Monty Dog
    Monty Dog Posts: 20,614
    Bar- tight = buggered chain & knackered hubs IME. Slacken it off a touch. Unless you are running top-end NJS chainset, hubs and chain there needs to be a bit of 'backlash' in the drivetrain.
    Make mine an Italian, with Campagnolo on the side..
  • mz__jo
    mz__jo Posts: 398
    It's not impossible that the problem might be caused by uneven chain wear (a tight spot). Chains for ss don't need to cost a fortune, try sticking a cheapy on and see if it has any effect on your problem. If it's that don't waste your time trying to play with rings (although a tight spot on the chain can be the cause of subsequent uneven ring wear). If the line is right it should be possible to have a useable transmission even with a bit of uneven wear.
  • andyrr
    andyrr Posts: 1,822
    Fitted new chain (gold KMC 3/32) and there was still noticable tight/slack discrepancy which I didn't seem to see much improvement from by loosening the chainring bolts. I think I need to slacken it off a little as I tend to run it very slightly too tight as opposed to too loose as I'm a bit paranoid about the chain jumping off the sprocket after having that happen a couple of times. I know, having run motorbikes for years, that too tight is bad as is too loose and getting a happy medium takes a biut of fiddling.
  • andyrr
    andyrr Posts: 1,822
    Still messing around with this :
    Chain is the newish KMC gold 1/8"
    I'd swapped to an older freehweel as the existing one was goosed but after about 4 days of being left in the garage unused I wheeled the bike out on Monday night awaiting use on Tuesday and - lordy, rough as a badger's, backpedaling felt dreadful, - really rough and stiff so, at 11:30pm I swapped to another, newly purchased, Shimano freewheel. Runs smooth and chain tension as per normal ie ok,ok, ok, tight, ok, loose but no more dramatic than normal.
    Riding to work I had repeated 'cracking' noises from the transmission - not 100% sure if it is the crank area (BB/chainring bolts) or rear (freewheel). Varied between almost once per rev to nothing for miles. On the way home I hardly felt any of these at all : it's like when the stress on the transmission is hard and constant (it's more uphill heading home) the issue isn't present. I was getting this about a year or so ago, Halfords nearest to my work (I know, I know ... but I'd bust a chain and some spokes on the way to work that day and the guys there were good enough to drop other jobs and sort me out) had reckoned it was a knackered headset noise being transmitted to other parts of the bike - sorry but it was not that, once I'd had new rear dropouts supplied by the dealer and chain tension a bit better the noise had gone. Or it had until now !

    Last night at home I got all 5 chainring bolts undone.
    Left these loose and twirled the pedals.
    Tightened them up having greased the bolts.
    Got the chain tension to a happy medium.
    Ride to work - crack, crack - aargh driving me mad !
    BB has no detectable play. Chain runs pretty smooth.
    Chainring (original on the Bontrager crankset) is showing signs of wear on the teeth so I might try to find an alternative - not sure the BCD - std track ?
    Whilst that awaits I might try rotating the chainring position to see if the chain tension can be evened-out.
  • andyrr
    andyrr Posts: 1,822
    This a worthwhile purchase ?
    http://www.wiggle.co.uk/token-tk140-track-chainrings/
    Token TK140 Track Chainring ? Seems quite cheap and Token a decent enough make ?
    I see a Wiggle review for it indicating the same issue as I currently have - getting good chain tension all round.
  • John.T
    John.T Posts: 3,698
    Intermittent cracking noises often caused by water in the hub bearings. You should be able to run a SS drive train almost to destruction without any trouble. And you will almost never get even tension.
  • Monty Dog
    Monty Dog Posts: 20,614
    How is the chainline? The cracking could be the chain sideplates catching on the edge of the chainring / sprocket
    Make mine an Italian, with Campagnolo on the side..
  • andyrr
    andyrr Posts: 1,822
    Well, I think the cracking noise may well have been the hub bearings - I greased the hub really well last night (obviously cheap hubs front and rear as there is a tiny window of smoothness where otherwise they turned roughly/had play but this AM's commute was ok.I had done this a few hunderd miles previously but it needed done again - will try to make it a monthly job from now on.
    I couldn't be bothered tbh to also spend time rotating the chainring to see if I can make an improvement to the consistency of the tension all the way round - that's next and also I think a new ring to be ordered soon since the existing one's teeth is getting worn and hopefully an improved quality one will be rounder.
    That Token one was the a 4-bolt : I need 5 : 130BCD I guess (will measure to be sure) ? Cheapest I found was a Brev one for £17.99o at Evans.