Bicycle chain (lower end) vibrates up and down during normal cycling

[NY]

My wife had her pedelec (electrically-assisted bicycle) serviced the other day. They needed to replace the chain. Since then the chain has been noisy during normal cycling in a higher gear, and the lower edge of the chain (between the pedal cog and the lower of the two derailleur tension cogs) slaps (vibrates) up and down several times a second - it looks as if the play is about +/- 1 inch.

This bike has a single speed on the pedal crank (unlike many bikes which have three different cogs) and 7 speeds on the rear cassette.

In the highest gear (ie the smallest cog selected on the rear wheel cassette) what should the relative positions of the two tensioner cogs be? The lower cog is a long way back (a line between the centres of the cogs is about 75 degrees - ie nearly horizontal). On my bike, which is a similar design though newer model, in the highest gear the angle of that line is about 45 degrees - ie closer to vertical), and there's no slapping of the chain.

I'm wondering whether the chain is a few links too long, so the tensioner is not pulling the take-up side of the chain strongly enough. It feels as if there is a reasonable amount of tension from the tensioners, and it feels roughly the same on her bike and mine.

I wanted to check before I phone and potentially make a fool of myself asking about something that may be normal.

[NY]

The vibration of the chain is only apparent during normal cycling, when there's a reasonably amount of force on the chain to overcome air resistance, friction and gradient. It's not apparent if you lift the rear wheel and turn the pedals with no load on the wheel.

[Harry Bloomfield, Esq.]

on 31/08/2021, NY supposed :

It might be an especially tight, or loose link, compared to the rest of the links. It should bed itself in, in time.

[Tim+]

If you?re not confident to do it yourself, take it back to the shop who changed the chain. Sounds like it is too long and needs a link or two taken out. It should be FOC if they?ve introduced a problem by changing the chain.

Tim

[Tim+]

It?s also possible that they?ve mis-threaded the chain through the jockey wheels. Either way, they should sort it.

Tim

[Pancho]

Tight links are normally most obvious at low tension, pedalling backwards for instance.

The rear cassette (7-speed cogs) is probably worn and needs replacing. It's a classic problem on normal push bikes.

[Tim+]

If the motor is in the bottom bracket, that?s a fair comment. If it?s a hub motor, I wouldn?t expect much cassette wear (although still possible).

Tim

[NY]

I phoned the shop and they said that it's normal for the two jockey wheels to be almost at 9 and 3 o'clock when the chain is on the smallest cog of the cassette; the jockey wheels move towards 12 and 6 o'clock as successively larger cogs (lower gear) are selected. So there's nothing to worry about there - they say a fair amount of chain slap is normal. I'd worried that as the cogs get closer to 9/3 o'clock, there may be less tensioning force to keep the lower part of the chain taut.

But the second problem was the chain noise. My wife said it was worst in a low gear. As I rotated the pedals slowly with a large cog / low gear selected, I could see each link of the chain was rubbing on the housing of the motor unit: there is a very narrow gap between the housing on one side and the flange which prevents the chain coming off the chain-ring on the other. When a large cog is selected (this is closest to the centre-line of the wheel) the angle of the chain makes it rub on the housing; when a small cog is selected (this is furthest away from the centre-line of the wheel) the angle of the chain alters and it comes closer to rubbing on the flange which prevents the chain coming off the chain-ring though it doesn't actually rub.

Looking at Youtube videos for replacing a chain-ring, there is a spacer which alters the position of the chain-ring on its shaft. I wonder if the service involved removing it and it didn't get put back, so the chain-ring is too close to the housing. I'd wondered whether the chain-ring was adjusted with a grub screw to lock it to the shaft after it had been slid to the correct position on the splined shaft, but the only adjustment is that spacer ring.

It's only a problem for the Bosch motor on my wife's bike. My own bike has a Yamaha motor and that is designed differently: there a loads of room (a couple of centimetres) between the chain-ring and the motor housing: a better design which doesn't run the risk of the chain rubbing on anything at one extreme or the other (very smallest or very largest cog).

I did find that there was a build-up of solidified grease on the housing in the two places where the chain rubs, and scraping that off with a fingernail makes it a bit less likely to catch. The old chain (they gave me it) is heavily coated in solidified grease which may lubricate the rubbing a bit more than an nice clean chain. So it may get better over time - as I think someone mentioned up-thread.

[Tim+]

Sounds to me like you need to take it take back to the shop. The chain should NOT rub anywhere or be noisy.

Tim

[Vir Campestris]

It occurs to me it should be rather easy to check

(a) are they the same width (b) are they the same length (number of links, not actual length)

Either of those being wrong might affect the symptoms.

Andy

[Paul]

Chains and teeth can wear at the same time.

If you change one of them, the new one might not mate all that well with the other.

On bicycles, there is a little tool you can buy to measure "chain stretch" (chain wear). I presume the purpose is to trigger buying another chain. But perhaps changing the entire drive train is more satisfying from a "symptoms" point of view (noise or actions).

I've done that once on my current bicycle. Because the bicycle was cheap, changing the drive train costs 25% of the purchase price of the bicycle.

Bicycle parts don't seem to wear like they used to.

*******

Sheldon Brown, I believe passed away a few years back, but others carry on the web site. There is all sorts of information here on bicycles, their care and feeding. Perhaps some aspect of wear or uneven wear on a part of the drive train, excites vibration in the new chain.

<===

Paul

[NY]

I think I've identified the cause of the chain vibration and the noise. When the bike is in the lowest gears (largest cogs, closest to the centre line of the wheel) the chain is rubbing on the housing of the motor. When it is in higher gears (smaller cogs, closer to the frame mounting of the wheel) the chain is at a different angle and does not catch on the housing.

Full marks to the shop which serviced the bike: after fitting the new chain, they left it in that state :-( I'm not sure how much the lateral position of the chain-ring (cog on pedal shaft) can be adjusted to compensate for this - looking at Youtube the only variable is the presence/absence of a spacing ring; there's no grub screw to allow the chainring to be slid along the splined shaft to the correct position and then locked into place. But that's the shop's problem. Means I'll have to put the bike carrier back on the bike again and take the bike over to the shop again (45-minute journey each way).

They already failed me by not fitting the backup battery in the bike computer on my brand new bike as part of the assembly and setup process. It's a normal CMOS battery, so it *should* be easy, but it means dismantling the headlight and the computer housing bracket to get to the battery compartment: unlike Bosch, the Yamaha computer is not removable (for anti-theft and for replacing the battery) on a quick-release mounting, and I didn't have the right socket-spanner-on-a-shaft tool to undo the nuts. And when they replaced the inner tubes on my bike with ones with puncture-reduction gel inside (at my request), they fitted ones with those stupid Presta valves instead of the Schrader (car tyre) valves that were on the old tubes. Presta valves really are the spawn of the devil: they need a little adaptor to be carried around, and they need the fiddly release nut to be undone before the pressure can be checked or the tyre can be pumped up, and then you need to remember to tighten the nut afterwards, so checking and pumping is a much slower process. Still, we have to carry one of those adaptors anyway because my wife's bike has narrower wheels which can *only* accept Presta valves, whereas mine has wider wheels which can take either.

The shop has an excellent sales department but their after-sales in the workshop leaves something to be desired.

[Andrew]

+1 Either replace both at the same time or neither. In my experience, sprockets wear faster than chains simply because there are fewer wear points on the sprocket compared to the number of rollers on the chain, so why did they change the chain ?. "Oh look, he comes a female with and electric bike; we can price-gouge her for a nice profit, they believe anything"

[Pancho]

Checking? Finger an thumb give it a squeeze. FWIW, Schrader is better, if they changed to Presta, or vice-versa, without asking I would be pissed and get them to redo it. They have no reason to suppose you have a Presta pump.

I don't know about electric bikes, but normal bikes are a DIY maintenance dream. Everything is like lego, very little expertise is required. At worst you need specific tools.

Not like the days when I remember dad cleaning out my sturmey-archer gears.

[NY]

No. I only noticed when I got the bike home and though "those valve stems look a bit narrow for Schrader".

Yes, pressing on the tyre is a good quick way of checking roughly, though I'm always surprised as how a tyre can *feel* hard yet be under-inflated, or can *feel* soft and yet be up to pressure.

I too think of Schrader as "real" valves and Presta as "toy" ones ;-) If I have to get the tubes replaced at any time in the future, I'll make sure I get ones with Schrader valves - assuming that gel-filled ones are available with that valve.

You need a torque wrench which can accept various bits - either spanner-type for nuts or Allen key (ie male/female). Even the back wheel needs to be torqued to the correct setting, and needs more than a simple Allen key that's a couple of inches long to get enough torque to *undo* it. I had to repair the puncture in my back wheel with the tube still around the wheel, which was easy enough though it meant I could only put a little bit of the tube at a time in a bowl of water to look for the leak.

With the right tools, yes it's easy and there are Youtube videos that people have done. When I was researching the position of the chainring for the problem of the chain fouling the casing, two specialised tools were needed: a crank puller (a threaded shaft) and a Bosch-specific disc with lugs on the side to undo the chainring. I'll probably get a torque wrench and a set of Allen key bits for it so I can at least remove the rear wheel if I ever need to repair a puncture without doing it in situ.

[Paul]

The chain is relatively cheap.

Even if changing it alone, isn't all that helpful.

With the tool that measures chain stretch, it's easier to have a criterion for replacement.

With the teeth on a sprocket, that's more of a judgment call. There are various kinds of damage to teeth. The Shimano ones with all the fancy machining, could have more "failure modes" than regular teeth. For me, I guess it's a matter of changing the chain, and if the situation is still bad, then contemplate new teeth for everything (except the derailleur).

All I can tell you is, the bicycle previous to this one, wasn't nearly as much of a "loser" as this one.

To give an example, my very first bicycle cost 1/7th what the current one cost (and the current one is not fancy particularly). I was able to use the bicycle seat (a perfect fit) for *40 years*. The bicycle seat, being as nice as it was, transferred from bike to bike. Until I couldn't tape the cracked plastic on it any more.

The bicycle seat on the current bike, it only lasted about three months. The replacement I got, isn't all that comfortable, but there's only one "style" for seats now, so ya "gotta suck it". There is little risk of the original seat in that case, being reused on any other bicycles.

The seat post on the current bike, was spring-loaded. The mechanism wore out in about a year and a half. I could hear a strange noise, and I thought it was the main crank bearing. But after a while, I figured out it was the seat post. And I replaced it with a plain seat post. And guess what - no maintenance since. Proving that plain pieces of pipe, are very reliable. There is no difference in the level of comfort (I try not to drive through potholes).

Paul

[NY]

The chain was clarted up with very sticky congealed oil from successive oilings (*) of the chain after pressure-washing the bike or after it hasn't been used for a while. I'm not sure why they changed the chain rather than just cleaning it, which is what I would have done: I've got the brush attachment on an aerosol can for cleaning the chain. They said the chain was replaced because it was congealed with grease, rather than because it was worn. I too wonder whether they went for the easiest option - though it may also work out as the cheaper one if it involved less labour time. I know there is a phenomenon called chain suck where a worn chainring can cause a chain to stick to the teeth slightly instead of disengaging cleanly. That's what I though was causing the chain vibration, until I turned the pedals very slowly and noticed each tooth in turn shifting a millimeter sideways as it passed the housing around the motor and crank bearing.

I might clean the old chain (so it is flexible enough to be able to handle so I can count the links) and compare it with the new one. The shop said it is normal with the smallest cog in the cassette for the jockey wheels to be almost 9 and 3 o'clock. I'd assumed that even with the smallest you needed a more upright position for the jockey wheels to be able to exert the tension - maybe ranging from 7/1 to 11/5 o'clock positions between smallest and largest cogs - +/- 45 degrees either side of vertical. I was wrong - apparently!

You tend to expect that if you take a bike (or a car) to be serviced, you will get it back in a better rather than worse state that when it went in ;-)

(*) I *did* use the proper bike oil for chain and bearings - not any old oil that wasn't intended for bikes.

[Pancho]

I would be dubious about "need" a torque wrench. Depends on your experience and common-sense. Allen keys you do need, longer ones are good.

[Tim+]

Not really. Easier to pump up as you?re not fighting a strong non-return valve and more leak resistant. Be that as it may, it?s not a good idea to use Presta valve inner tubes in rims drilled for Schrader valves.

Take it back and tell them to fit the correct tubes. They might not be able to get schrader valve tubes pre-filled with gel but that?s no excuse for fitting the wrong ones.

You really need to speak to the manager and tell them to sort out the mess that they?ve made.

Tim

[Tim+]

Not in my experience. I?ve changed many a chain without changing sprockets and never had a problem. Yes, sprockets do wear and a new chain on a worn sprocket will cause problems but I?ve always found that sprocket life is way longer than chain life. Changing sprockets *every* time you change the chain is unnecessary IMO.

Tim