loud 'crack' in the drive train when cranking hard

NIGEL_ASH

Any suggestions please...

When cranking hard I'm getting a loud distinctive 'crack' in the drive train. I've been through plenty of mud etc lately but always diligently clean the bike after each outing. Thinking it may be the chain, I've replaced this with a SRAM and powerlink but the problem still exists.
I checked the cranks/bottom bracket for play when the chain was off and it spins perfectly and has no play.
I've also remove the pedals (SPD 520's) and clean/regreased the spindle threads before refitting. The pedals seem fine, no play etc
So, i'm thinking maybe bottom bracket still but am surprised as the bike is only 4 months old

Is there anything else it could be?

nicklouse

what gear does it happen in?

where are the cranks when it happens?

what is the drive train?

Banned!

are the bolts holding the chainrings on tight enough?

NIGEL_ASH

it tends to happen in higher gears, i.e largest chainring and smaller cogs at the rear.

The drivetrain is Shimano as fitted to a Mongoose Otero Elite,

Crankset Shimano FC-M3118 42/32/22T
Bottom Bracket Shimano ES25 Octalink BB

It happens when applying power on the down stroke of the cranks, particularly when the right crank. When off the bike, if I put the right crank at about 2 o'clock and press hard down on it while supporting the bike, the noise can be heard and felt through the crank. Its not the pedal as it does this with the pedal removed.
Have inspected the frame for any cracks and can't see any

NIGEL_ASH

Jesus_Christ wrote:

are the bolts holding the chainrings on tight enough?

Thanks, i'll check that tomorrow

JimmerG

I wonder if its the pawls in the freehub cracking into place, sometimes they get a bit gunked up and struggle to settle properly. It does make one loud and disturbing crack every now and again when you push on the pedals. Its not catastrophic, and should sort it'self out - its certainly not as bad as it sounds...

You could try giving a good soak, or a blast with some degreaser, then a blast with some thin lubricant.

Big G Specialized

Good morning, after browsing through Bikeradar as a guest decided to sign up after reading about your 'concern' :?

I experienced a very similar problem and thought it was the main crank bearings that had lost their 'ovelness' or indeed that the crank was broken - took the bike to my local cycle store to be informed that it is indeed the freehub that was worn...it's something to do with the grease packed inside i losing its viscosity - there is a temporary fix to this problem and i couldn't believe it when I was informed as to the solution - urinate on the back cassette (if out on a ride) thereby freeing up the grease. It apparently freezes up especially in cold weather.

Of course that is only temporary - the right thing to do, is replace said freehub at about £12-00 plus fitting or if mechanically adept do it your self. As your bike is only a few months old it should be covered under warranty I should think - mine (Specialized Hardrock Sport) is 4 years old so one would expect to replace things at that age

Hope this helps - peace and free-ridin to all[/b]

nonnac85

I had a similar thing happen to me a while ago - after exploring various options it turned out to be the mech hangar had a crack in and was snapping in and out of position!!

mr boos

could be bottom bracket has taken in water and rusted(power washing?) or a rear wheel bearing, that can sound like its coming from the drivetrain,it could be twisting the rear wheel a tad under load

NIGEL_ASH

Problem sorted.

I took the cranks and chainset off, inspected the bottom bracket but was so horrified at the weight of the cheap steel chainset I decided to upgrade with a Deore chainset and therefore a new bottom bracket (removed 73 x 121mm and fitted a ES51 73 x 113mm)
Also had to buy the crank removal tool and BB removal socket, not cheap but I have them now for future use so no bad thing.

Fitted the new kit, problem still there. So removed cassette and freehub and cleaned, greased and replaced.

So, a new chain, new BB, new chainset and a couple of special tools later and finally the problem is sorted.
I'm glad I didn't hand the bike to an LBS though, learning plenty by fettling and doing the work myself

allthegearnoidea

its a great feeling when you manage to fix nigles like this on your todd as such, like you said, best way to learn about your bike!