leefreeman97
New Member
- Location
- Bexhill=on-sea
When I pedal the middle of my bmx makes a donk noise. I've taken the crank out greased it put it back in correctly but it still makes the donk noise, could someone help me please?
something in the middle of my bmx is making a donk noise?
- Thread starter leefreeman97
- Start date
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Sounds like a bottom bracket issue to me. When you say you took the crank out, which part exactly do you mean? Just the cranks alone, or the bottom bracket bearings too? A picture of your setup would probably help identify things here. 
Oh, and welcome to the forum!
Oh, and welcome to the forum!
OP
OP
leefreeman97
New Member
- Location
- Bexhill=on-sea
I took the crank and bearings and thanks
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leefreeman97
New Member
- Location
- Bexhill=on-sea
Ok, so you have an American style one piece crank/bottom bracket! When you took the crank off, was there any obvious wear or pitting on the bearing surfaces, or even the bearings themselves? This would obviously indicate the need for a new bottom bracket.
If not, when you grab the top of the crank, near the pedal, and try to move it side to side (in relation to the bike), is there any play? This would indicate an incorrectly adjusted bottom bracket. Similarly if there is any resistance on the cranks when back-pedalling, the bottom bracket is adjusted too tight. If all of this is fine, and you've stripped and serviced the bottom bracket, and rebuilt with new grease, you can probably start looking else where.
How often does the noise occur? Once per revolution of the cranks would indicate either bottom bracket (which we've in theory ruled out if you've got this far and the noise persists) or pedals. So go ahead and check the pedals. Is there play in the bearings? Are they rough or dry?
If the pedals aren't the issue, move on to the rear wheel. A donk from the rear wheel will more often occur once per revolution of your wheel, rather than once per pedal stroke. Take the rear wheel off and try spinning the axle in your hand. Again, if it feels rough or dry of grease then you may need new bearings. If the axle is hard too turn by hand, or has play in it, it will either be worn or just badly adjusted. You'll most likely need a cone spanner to properly adjust the hub, so either buy/borrow one or send it off to a bike shop.
If it only happens when you're pedalling, it is more unlikely to be the front wheel, but you can check it as above. Wheel bearing noise will generally continue when you stop pedalling, so this is a good way to rule out the bottom bracket and pedal area.
Remember to also check for things you think are silly! Loose saddle, item of clothing flapping on the frame etc have all been known to create noises that we just can't trace.
It will most likely be one of the bearings on my list above, so give them a look over and see what you find!
If not, when you grab the top of the crank, near the pedal, and try to move it side to side (in relation to the bike), is there any play? This would indicate an incorrectly adjusted bottom bracket. Similarly if there is any resistance on the cranks when back-pedalling, the bottom bracket is adjusted too tight. If all of this is fine, and you've stripped and serviced the bottom bracket, and rebuilt with new grease, you can probably start looking else where.
How often does the noise occur? Once per revolution of the cranks would indicate either bottom bracket (which we've in theory ruled out if you've got this far and the noise persists) or pedals. So go ahead and check the pedals. Is there play in the bearings? Are they rough or dry?
If the pedals aren't the issue, move on to the rear wheel. A donk from the rear wheel will more often occur once per revolution of your wheel, rather than once per pedal stroke. Take the rear wheel off and try spinning the axle in your hand. Again, if it feels rough or dry of grease then you may need new bearings. If the axle is hard too turn by hand, or has play in it, it will either be worn or just badly adjusted. You'll most likely need a cone spanner to properly adjust the hub, so either buy/borrow one or send it off to a bike shop.
If it only happens when you're pedalling, it is more unlikely to be the front wheel, but you can check it as above. Wheel bearing noise will generally continue when you stop pedalling, so this is a good way to rule out the bottom bracket and pedal area.
Remember to also check for things you think are silly! Loose saddle, item of clothing flapping on the frame etc have all been known to create noises that we just can't trace.
It will most likely be one of the bearings on my list above, so give them a look over and see what you find!
OP
OP
leefreeman97
New Member
- Location
- Bexhill=on-sea
I have checked my bottom bracket and its fine, there's no play when I pull the crank side to side and I've checked my bearings and they are nice and greasy also, the noise happens once every revolution.
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leefreeman97
New Member
- Location
- Bexhill=on-sea
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leefreeman97
New Member
- Location
- Bexhill=on-sea
does the inside of my back wheel bearings look ok?
Smurfy
Naturist Smurf
- Location
- Smurfette's Kitchen
I don't know. Is that browny coloured stuff rust or grease?
Not helpful, but donk related
Blackout Crew - Put A Donk On It - Out Now: http://youtu.be/ckMvj1piK58
Blackout Crew - Put A Donk On It - Out Now: http://youtu.be/ckMvj1piK58
Learnincurve
Senior Member
- Location
- Chesterfield
This may sound absolutely obvious but a online acquaintance of mine just spent 2 days taking his bike apart and rebuilding it only to find the strange noise was a stone inside his frame, all he needed to do was take the seat post out and turn it upside down.
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OP
leefreeman97
New Member
- Location
- Bexhill=on-sea
The brown stuff inside is grease and I have tried taking the seat post out and turning the bike upside down but nothing came out.
Hard to tell from the photos. All bearing surfaces should be completely smooth. No rust, pitting, dirt or other general bumpy bits. Same for the ball bearings. If any of this is present, it needs to be changed.
Smurfy
Naturist Smurf
- Location
- Smurfette's Kitchen
Need to wipe the grease away. The bearing surface should be very smooth, as should the balls and cones.
I'd advise leaving the grease in his hubs. Replace it with fresh stuff, by all means, but don't just wipe away, it's kind of important.
Edit: Unless you were meaning wipe the grease away to check the bearing surface, then replace, in which case valid suggestion, and my mistake!
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