Diagnosing "clonk" in drive train.

[LittleGreyCat]

My Spa Wayfarer developed a rather unnerving "clonk" during my last ride.

Only when my right pedal passed through TDC.

Further, it was most noticeable when climbing slowly in low gear when it was a really loud "donk" which could be felt through both pedals.

Mid ride I checked the hex head bolt that held the chain rings and pedal on for tightness but that seemed fine.
I suspected that because my most recent fettling was to swap a 28 inner ring for a 24.

Confusingly, once I stopped climbing short steep hills the noise went away and all was smoothness again.

I haven't had much time to diagnose, but I can't find anything obviously loose and when spinning the pedals with the bike on its wall hook there is no obvious TDC "clonk".

The symptoms seem to match some play in the chain between the front rings and the rear cassette and an uneven pedalling style, where my leg lets the chain slacken just before TDC on the right and then tightens it as the crank goes over TDC. I am right leg dominant so the same condition may not apply to my left leg. However why all of a sudden?

Oh, I did also service (clean and lubricate) the wheels on the rear derailleur but I'm struggling to see why this would cause such an effect.

I did wonder about a sticky pawl in the freewheel. That is, assuming that there are multiple pawls, that after a brief pause in the pressure on the freewheel allowing the wheel to go faster than the cassette, the first pawl did not engage and the freewheel slipped until the next pawl engaged with a bump. Although I have no idea if that is the way this freewheel works. Just thinking back to the issues I had freeing off an old sticky freewheel a couple of years back.

Does any of this ring any bells with anyone?

[DevonDamo]

My money would be on your cassette being slightly loose on the freewheel - i.e. the retaining ring needs tightening. If that's what it is, and you have the right cassette removal tool, then it would be a very quick fix. (The 'clunk' is caused by the cogs on the cassette shifting in relation to each other as they're only riveted together so their stability depends on them being held in a vice-like grip between the inner flange of the hub and the retaining ring.)

[slowster]

There are probably multiple possible causes, but the first two that spring to mind reading your description are:

1. One or more loose chainring bolts securing the new inner ring.

2. Right hand crank touching the front derailleur, e.g. as a result of frame flex at the bottom bracket under the stress of using a low gear/high torque (so it will disappear when riding on the flat). I would have thought this was much less likely, especially on a modern steel frame like the Wayfarer designed to be able to cope with heavily laden touring, as opposed to an older lightweight frame with less stiff, narrower tubes. Nevertheless I seem to recall that you have a relatively large frame size, which might exhibit a little more bottom bracket flex than a typical medium frame.

Something else I would also check is that the bottom bracket cartridge cups are not loose on either side.

[Jdsk]

I'd take the chain and pedals off and see what you can feel when turning the cranks with your fingertips.

Then heave the cranks in all possible directions.

(Crossed with that comment about BBs.)

Jonathan

[Marcus Aurelius]

Put a dab of lube on the dropouts / axles, and check the tightness. You’d be surprised how many times noises like that aren’t coming from where you think they are.

[colin54]

Have a read of this previous thread on the subject :-
viewtopic.php?t=64077
Good luck.

[Brucey]

if it wasn't clonking before, you should be suspicious of the most recent changes. I therefore concur with the suggestion to check the chainring bolts (which hold the chainring to the crank) first of all.

I'd also note that if the chain is still the old one and it is worn, I wouldn't expect it to run smoothly on a new chainring.

cheers

[PT1029]

My bet is a slightly loose in its thread BB cup.
To check, by hand, push cranks from side to side FIRMLY. I say firmly, as sometimes cups only move on the treads under higher loads. If you feel any movement as per a slightly loose BB bearing, look at the interface between the RH (and then LH) BB cup and the frame. You may well see a bit of movement between the BB cup and the frame. Here movement would be a slight rocking with in the threads.
I quite often see this on newish bikes (Trek, Ridgeback* and a few others) after a while of use.
If it is this, remove cranks, LOOSEN LH cup a bit so you can tighten RH cup fully into frame, then tighten LH cup.
While you are at it, if Spa use as much grease on BB threads as Specialized/Ridgeback, before tightening the BB cups, I'd take them out and grease the threads liberally before reassembling. I'm assuming a cartridge bearing here, so no loose balls to fall out.
*Oddly with Ridgeback, if the BB cups come a bit loose, often I can't get the cranks off (or have great difficulty) because they have been bolted on so tight at the factory. They should move the gorilla from crank bolt duty to BB cup duty. Any sensible bike shop will be checking the crank bolts when they assemble a bike anyway.

Sometimes a slightly loose pedal thread can give the same knocking feel. If so, you might like to check thread grease/copper slip content while you are at it

[peetee]

If this is happening in first gear I’m inclined to think it’s torque related as you have lowered the gear ratio. Probably the rear hub freewheel bearings or as suggested earlier a cassette location issue or a gear wear mismatch between cog and chain.

[LittleGreyCat]

if it wasn't clonking before, you should be suspicious of the most recent changes. I therefore concur with the suggestion to check the chainring bolts (which hold the chainring to the crank) first of all.

I'd also note that if the chain is still the old one and it is worn, I wouldn't expect it to run smoothly on a new chainring.

cheers

New chain was fitted along with the new chainring.

Thanks to all for the suggestions; it will give me various avenues to pursue.

[Brucey]

there are all manner of things that might be loose and move, but if the clonk is (not quite as you describe) really a slip as well and it occurs when you are mid power stroke, under load, it just might be a new chain slipping on older sprockets....?

cheers

[LittleGreyCat]

there are all manner of things that might be loose and move, but if the clonk is (not quite as you describe) really a slip as well and it occurs when you are mid power stroke, under load, it just might be a new chain slipping on older sprockets....?

cheers

Despite reading all the sage advice here I still struggle with the concept of the sprockets wearing out in a year and somewhere over 1,000 miles on the road.[ Hmmm....20 miles a week for a year is around 1,000 miles. Possibly a bit more, then? Ah. Odometer says 1874 miles.]

It isn't that long since I put another new chain on, following the advice about changing chains on a fairly regular basis.

I am (old MTB) used to running a chain until, well, forever.
Still on the original chain rings and cassette on my 90's MTB, although I'm sure I've changed the chain at least once.
I know I replaced the rear derailleur a few years back.
Possibly the difference between a 7 speed and 9 speed?

If it is new chain/worn sprockets can I assume that the chain will bed in after a while?
I will still check the other suggestions.

[mig]

front mech knocked out of line with the chainring fettling and now something hits it at TDC with the chain innermost (not when outermost and cruising around.)

[Brucey]

if you want not to buy new sprockets and chainrings as often (and you shouldn't, they are by far the most expensive parts of the transmission) then you should change the chain regularly before it gets too worn. If you use cheap chains and don't maintain them particularly well, they can last about 1000 miles before they elongate too much (through wear) and this starts to wear the sprockets and chainrings at an ever increasing rate.

If you carry on using the chain and sprockets together past this point then they will usually carry on working acceptably well, long after the point at which the sprockets are too worn to accept a new chain. Chances are that your old 7s MTB transmission has been like this for a long time, and it'll need new parts all round when the time comes.

Whenever you have more sprockets at the back, it is arguably of greater benefit to change the chain more often. The reasons for this are severalfold

1) the sprockets wear faster (for any given state of chain wear) when they are made narrower
2) the price differential between chains is often a lot less than the price differential between cassettes and chainrings; e.g. a half decent 9s or 11s chain isn't necessarily twice the price of a 7s chain but the sprockets are more likely to be.
3) the shifting goes to pot more quickly with a skinnier chain; the derailleur can only push the chain around if it is laterally stiff enough, and skinnier chains become laterally flexible (through wear) much faster than wider ones.

If the clunk varies depending on which sprocket you use at the back, it may suggest that it is a chain slippage problem. Eventually it may settle down, but until it does, each clunk might just break a chain roller or sprocket tooth. What happens under load is that the chain doesn't feed onto the sprocket properly as it leaves the derailleur, and sits on top of the sprocket instead. As this part of the chain comes to the top of the sprocket, it drops into the teeth suddenly and you feel a big clunk. Usually the chainring is big and the sprocket small, so the clunk happens during the power stroke; however if the chainring and sprocket are of comparable size, the clunk will occur appreciably after the middle point of the power stroke.

FWIW a really worn sprocket is obvious, but the difference between one that will skip (under load) and one that won't might be measured in microns, so if there is the slightest wear it is almost impossible to say it will or won't work without trying it.

cheers

[slowster]

Apologies for stating the bleedin' obvious, but when a problem like this occurs where:
- it's not possible to immediately diagnose the cause
- there are multiple possible causes
- the problem might be manifesting itself somewhere on the bike some distance from/seemingly unrelated to the actual cause (e.g. a noise at the crank caused by a fault with the hub/freehub/cassette),
then it's usually advisable to try initially to isolate the problem by a process of elimination while riding, especially since to begin with such problems are often only apparent whilst riding and cannot be replicated with the bike in a workstand.

Therefore if the problem appears when riding uphill, make various changes one at a time (separately) while riding uphill to see if they make a difference, e.g.
- change gear between the front rings
- change gear between the rear sprockets
- compare different extreme front/rear gear combinations (e.g. is the problem with big ring/rear second largest sprocket better or worse than with small ring and second smallest sprocket)
- with a noise or knock at one part of the pedal stroke try pedalling with just the left foot, and then switch to the right foot (if you don't/can't actually take one foot off the pedal, try not to put any force through it and just use the other leg to push the crank through 360 degrees)
- try riding out of the saddle

This approach will often at least narrow down the likely possible causes and give you a better idea when you get off the bike of where and what on the bike to investigate more closely.