Non (ish) spinning chainwheel

[Pendodave]

I have an old mid 90s ish specialised rock hopper mountain bike that I use for local chores and the odd tour when wider tyres or lower gears are required.

I was cleaning it the other day, and noticed that when the chain is not attached, the chain wheel does not spin very freely. I can probably get 1 full turn out of it if I give the pedals a good shove. My much newer road bike spins pretty well when treated similarly.

The chain wheel doesn't squeak or grind or feel rough, either when spinning it by hand or when a chain is attached and I'm pedaling.

Now, I assume that this is not normal. The question is, what is to be done? How many precious Watts am I losing?? I know nothing of bottom brackets. I have changed the chain wheel with a slightly odd tool, but nothing more. The bottom bracket is pictured below. Is it something I could replace, or is simple maintenance required? So many questions ...

[531colin]

It’s a sealed unit square taper bottom bracket.
Just replace it; you need to know the axle length, remove the old unit and measure, unless it’s still legible when you get it out.
It’s a JIS taper for Shimano cranks

[Brucey]

it is not possible to be absolutely certain from one such photo but that looks like a shimano cartridge BB to me. Whichever type it is, the fact that it doesn't turn freely means that the BB is crying out for grease, adjustment or both.

[slowster]

It may be worth watching all three videos below, because they give an indication of how easy or how difficult it might be. If the bottom bracket cartridge has been there for 30 odd years without ever being removed, there is probably a good chance it will be difficult to undo.

What tools you need will depend in part on whether it is seized in the BB shell, i.e. how much leverage you need to be able to apply. I think this is one of those tasks where if the unit was installed with grease or anti-seze only a few years ago, you are more likely to get away with using a cheap generic version of the Shimano pattern tool, whereas in your case I would make a point of getting the genuine Shimano tool or the version made by Park Tool or Pedros. If you have a breaker bar, whether the drive is 3/8" or 1/2" will determine which tool to buy. With a siezed cartridge the Shimano tool can be fastened in place with a purpose made tool like the Pedro Holder (https://pedroseurope.eu/products/bb-socket-holder-ii) or a DIY equivalent assembled with a bolt and large washers. If used with a breaker bar the Park Tool and Pedro tools have to be pressed against the cartridge to stop them camming out and damaging the splines, which is awkward if the cartridge is seized and you need to exert a lot of force at the same time on the breaker bar.

[Pendodave]

Thanks all.
Will be chewing on these. Probably before paying my local bicycle repair man a visit!

[gregoryoftours]

Only spinning once around with a fair shove will be wasting quite a bit of effort and it's definitely not right.

Can you take a photo that shows the back of the chainset on the drive side? Just to make sure that the bottom bracket spindle is long enough and that the chainset isn't bottoming out either in the bottom bracket drive side cup or against the chainstay of the frame.

Having eliminated those possibilities there could be a couple of other causes. The bearings could be shot inside the bottom bracket, and/or the non drive side cup could be over torqued and pressing too hard against the cartridge bearing on that side causing it to bind up.

In any case you'll need a Shimano compatible internal cartridge bottom bracket removal tool. Ideally a fairly low profile one that will be stubby enough to be able to use the crank bolt to hold the tool in place and stop it camming out in use.

After removing the cranks but bb still in the frame first confirm that the spindle is stiff or can't be turned by hand. If ok it should turn easily and smoothly.

Before using the bb tool it's probably worth leaving a bit of spray lube on the threads to soak in for a bit first.

Second I'd try backing the non drive side cup off a full turn, (thread is normal direction and you may have to loosen the crank bolt a bit if you're using it to hold the tool in place) then make sure the fixed cup on the drive side is tight in the frame - reverse thread so anticlockwise (edited) looking at it from that side of the bike. Then again check if the spindle turns smoothly, stiffly or stuck. If it now turns smoothly it's a sign that the non drive cup was too tight, in which case nip it back up but not so tight that it starts to bind back up again.

If it feels rough or stiff to turn with the drive side cup tightened up but the non drive side backed off then it's likely that your square taper bottom bracket is knackered and you need another one. Remove and try to read the specs - you'll need to order one of the same bb shell width and spindle length assuming the current one is correct- either 68 or 73mm and 113-115, for example would be fairly typical for an MTB triple of that vintage, yours looks like it may be an Alivio or similar Shimano model.

[Pendodave]

A quick update.
Thanks for all input. The linked videos above were particularly entertaining.
In the end, rather than buy a tool and wrench handle which I'm unlikely to use often, I took it down to a man and paid to watch him do it for future reference.
It took a lot of effort to remove, and there was some thread damage and some corrosion in the shell. Threads had to be re-tapped. I'm relieved in a way, because I dont think I could have managed it so don't begrudge the hourly rate.
I now have a lovely free spinning crank. At a cost of probably half the value of the bike...
The thing is, even though it's a pub/shopping/errand/lock up in public machine, it still needs to work properly.

[keyboardmonkey]

Thanks for the update - glad you got sorted. I always like to read this sort of thing, especially when others have gone to the trouble of posting detailed advice.

[cycle tramp]

Deleted

[Pendodave]

Thanks for the update - glad you got sorted. I always like to read this sort of thing, especially when others have gone to the trouble of posting detailed advice.

Haha. Indeed.
I sometimes offer up advice on other topics and it's always nice to get a response.
In this instance, it's (almost) entirely self interest though - I get the occasional need to tap the generously offered expertise here, so it probably makes it more likely I get a response when I need it.
I also think that it's more helpful for future reference if someone is searching with a similar problem and sees the eventual outcome.