CBR250RR knocking sound at low revs

[0li123]

I have a 1992 CBR250RR,

Just recently I have noticed a faint knocking sound coming from the engine at low revs, between 2000-5000 I have only noticed it in gears 1,2 and 3 but I think this is just because these are the only gears that I use within this range. It doesn't seem to have any effect on the performance of the bike but surely cant be a good thing. If anyone has any ideas what might be wrong please let me know, id greatly appreciate it.

Cheers

[Akzle]

I have a 1992 CBR250RR,

Just recently I have noticed a faint knocking sound coming from the engine at low revs, between 2000-5000

i'd say it's definitely a knocking noise in the engine.



ps. check chain tension.
could be piston slap, could be big end bearing going, could be no problem.

[0li123]

i'd say it's definitely a knocking noise in the engine.



ps. check chain tension.
could be piston slap, could be big end bearing going, could be no problem.

it doesn't make the sound when stationary and idling, only when I am taking of or at very low speeds, so does that rule out piston slap?

[Akzle]

it doesn't make the sound when stationary and idling, only when I am taking of or at very low speeds, so does that rule out piston slap?

via the awesome powers of the internet, i can tell you for sure, that you have a honda.

and unless you're lying, i can tell you for sure, that there's a knocking noise happenin with the engine.

it doesn't rule out piston slap. or anything else.
did you check the chain?

[0li123]

via the awesome powers of the internet, i can tell you for sure, that you have a honda.

and unless you're lying, i can tell you for sure, that there's a knocking noise happenin with the engine.

it doesn't rule out piston slap. or anything else.
did you check the chain?

Yes I have a Honda and yes I have a knocking noise happening with the engine. I have checked the chain and I think it could do with a tighten and a lube.. I Have had a couple of big rides equalling about 2000 km since I last tightened it so would probably be a good place to start

[FJRider]

Yes I have a Honda and yes I have a knocking noise happening with the engine. I have checked the chain and I think it could do with a tighten and a lube.. I Have had a couple of big rides equalling about 2000 km since I last tightened it so would probably be a good place to start

Forget the chain. Sort the knock out first. A well lubed chain won't fix that on the side of the road.

You will hear the knocking sound as power is applied. (won't hear it at idle as no power is being applied)

As for what it is ... revving an engine to 19,000 rpm wont help it's longevity ... for long. Things wear out ... tolerances get excessive ... bearings fail ... gudgeon pin wears ...

Bluntly ... everything inside the engine casings get loose. Later on ... something lets go.

Take a guess what actually lets go. Everybody else will ... but keep riding it ... and we'll see who's right.

[FJRider]

Oh and MY guess is main bearings ...

[Akzle]

well OP, now you met our resident-retard FJ.

as some kind of lesser mortal, i don't expect you to be able to identify what the noise is or where it's coming from.
noise of the chain jumping the sprocket will be transmitted through the entire gearbox/case/engine.

how many kms has the bike done?

[Asher]

Try answering "who's there" everytime it does it, eventually it will get so annoyed by you it will throw a big end bearing in protest.


The obvious way to check if its the chain or not is if it does it with the clutch in. Or take a fairing off and hold your hand over the top and bottom of the cylinder and try and feel where the knock is coming from.

[Paul in NZ]

I have a 1992 CBR250RR,

Just recently I have noticed a faint knocking sound coming from the engine at low revs, between 2000-5000 I have only noticed it in gears 1,2 and 3 but I think this is just because these are the only gears that I use within this range. It doesn't seem to have any effect on the performance of the bike but surely cant be a good thing. If anyone has any ideas what might be wrong please let me know, id greatly appreciate it.

Cheers

Does the knocking sound happen when you are applying throttle to the engine and go away when you are on the over run?

If its just a sound it can be pre ignition or pinking but if its a vibration it may be something as simple as a loose engine mount etc.

[ducatilover]

Ride it to Te Puke and I'll have a look at it for you

I would:
Check, adjust, lube chain.
Check for play on the output shaft
Check the clutch hub and bearing.
Check the steering head bearings
Check for end float on the crank (if it has any, you'd certainly know about it)
Listen for valve noise
Carbs out of sync can make some interesting noises too
Drop the oil and pick up screen and check for sneaky little bearings floating around...

If you're getting piston slap you'll have a fair amount of blow by on a cold leakdown test



Fortunately we can rule out cam chains as it hasn't got one and a stripped tooth on one of the gears doesn't seem to happen

[Fast Eddie]

is there a midget in the underseat storeage compartment? I had one on my 89 cbr250r and he made a hell of a knocking noise until I let him out..

[Akzle]

geez guys. you took long enough. i thought i's gonna have to carry this one by myself...

[ducatilover]

geez guys. you took long enough. i thought i's gonna have to carry this one by myself...

You could have solved it with all that solid advice you were giving

I know that it's a Honda now and the knocking is his heart beating for his boyfriend

[0li123]

Ride it to Te Puke and I'll have a look at it for you

I would:
Check, adjust, lube chain.
Check for play on the output shaft
Check the clutch hub and bearing.
Check the steering head bearings
Check for end float on the crank (if it has any, you'd certainly know about it)
Listen for valve noise
Carbs out of sync can make some interesting noises too
Drop the oil and pick up screen and check for sneaky little bearings floating around...

If you're getting piston slap you'll have a fair amount of blow by on a cold leakdown test



Fortunately we can rule out cam chains as it hasn't got one and a stripped tooth on one of the gears doesn't seem to happen

Buger, thats where I was this weekend and where I first heard the knock, oh well.. it seems a little temperamental as I rode to work today and didn't hear a thing. I will try and check as many of these as I can but im not to sure how far I will get, but thanks for the input. the bike has done 44000km by the way