Crank jamming

[Big Nick]

Weird issue with the crank today on my commuter hack

Got a clicking followed by the crank locking as I pedalled. It did it 3 or 4 times and on each occaison it freed itself off when I pedalled backward before freeing completely

I thought perhaps a small stone had flicked up and got jammed in the crank?

Any ideas?

 

[Shut Up Legs]

How old is the bottom bracket? Perhaps the bearings have run out of grease, and were seizing?

 

[Big Nick]

Hi victor, its an old bike, 20 years old in fact but lightly used in that time

There hasn't been any excessive grinding from the bottom bracket/crank prior to this occurring

If it happens again I will get the crank out of the BB and check the bearings, are the bearings likely to be a sealed unit or will they be loose and removable to check individually on a mtb of that age?

 

[Rickshaw Phil]

Sounds like chain suck - where the chain hangs up on the teeth and wraps round the whole chainring 'til it can't turn any more. Mine did this to me on a recent ride when I attempted to change down to low range - caught me unawares and I fell in a ditch.

If it is this it's often a sign of a worn chainring. The clicking may also be related to the gear indexing being out of adjustment. That's my guess without seeing the bike.

 

[Cyclist33]

"chainsuck... if it is this it's often a sign of a worn chainring. "

Twas what I would have said.

For info, my mtb has suffered from this almost since the first day I got it brand new. It doesn't help when trying to commit to a bit of trail!

Stu

 

[Big Nick]

The chainring doesn't look worn and I wasn't changing gear at the time, the bike has a triple chain set and I was on the big ring in a middle gear

The bike's been ridden in some torrential rain lately so I'll clean the chain, rings, cassette and relube whilst checking for grit and alike

I adjusted the gear indexing around a week ago but its now slicker than ever and rode fine up until today?

 

[Cyclist33]

The chainring doesn't look worn and I wasn't changing gear at the time, the bike has a triple chain set and I was on the big ring in a middle gear

The bike's been ridden in some torrential rain lately so I'll clean the chain, rings, cassette and relube whilst checking for grit and alike

I adjusted the gear indexing around a week ago but its now slicker than ever and rode fine up until today?

See above, mine has been doing this since day one. I dunno what it is caused by, but presumably either the chain's link(s) or (one or more of) the chainset's teeth... It *is* possible to get substandard parts as new build... so if your bike ain't new...

 

[Smurfy]

my mtb has suffered from this almost since the first day I got it brand new.

Same as my very first MTB. Just a few miles of riding in, still all shiny and new, and I got the mother of all chain jams between chainring and chainstay. Made a terrible mess of the paint, and slightly bent the chainring. Not happy!

 

[young Ed]

Same as my very first MTB. Just a few miles of riding in, still all shiny and new, and I got the mother of all chain jams between chainring and chainstay. Made a terrible mess of the paint, and slightly bent the chainring. Not happy!

excuse to up grade chain rings!

and the BB is likely to use loose bearings at that age, assuming it is the original BB that is. it is only the more modern and slightly more expnsive bikes that use sealed systems such as shimano un54/5 and external bearings such as shimanos hollowtech systems and compagnolo and some other makes also have external bearing BB's and the very high end ceramic BB's
Cheers Ed

 

[Smurfy]

excuse to up grade chain rings!

After buying the bike I didn't have any cash left! Nowadays I've got a bit more money to spare, and I've recently blown some money on an EAI Superstar.

 

[mrandmrspoves]

Take the chain off the chain rings and try revolving the crank and see if there is any side to side play on it. Although this could be chain suck as described above, it could also be the crank jamming due to damaged bearings when two damages surfaces come together. Pedaling backwards would dislodge the locked bearings - so this would be where I would place my bet (if I were a gambling man - which I'm not, because I would lose all my money!)

 

[raleighnut]

It could be the steel carrier that spaces the bearings apart, these can wear to a knife edge which causes the locking. This can also happen to headrace bearings as well. Only way to tell is strip it down.

 

[Big Nick]

The BB was grinding very badly once I got the crank arms off so I'm fairly confident this may be the cause of the lock up, with all the rain the chain was also not that well lubed so I've cleaned and relubed that as well

Commuting duties on Monday for the old steed so I'll see how it goes

Many thanks to all for the advice