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Knocking after checking valves?

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Laamapalmu
Two Stroke Sniffer



Joined: 23 Dec 2015
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PostPosted: 09:41 - 25 May 2016    Post subject: Knocking after checking valves? Reply with quote
Hello

I have an Derbi 125cc Baja and it made a knocking noise.
I re-adjusted the valve clearance and tightened the valve screw nut to 14NM which is used in most CB/CG125 engines.
I started riding and slowly the knocking came back after it was working well. Any ideas what might be the problem and how could it be fixed?

So the engine is basically an CB125 but an chinese clone. Cam chain and tensioner are ok. Neutral
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Islander
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PostPosted: 09:58 - 25 May 2016    Post subject: Reply with quote
Excessive valve clearances usually cause a tapping rather than a knocking noise. Try pulling the clutch lever in while it's running in neutral - does the noise stop if you do?
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Laamapalmu
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PostPosted: 10:45 - 25 May 2016    Post subject: Reply with quote
Islander wrote:
Excessive valve clearances usually cause a tapping rather than a knocking noise. Try pulling the clutch lever in while it's running in neutral - does the noise stop if you do?

No, pulling clutch doesn't help and the sound is the same in every gear and get's louder when giving throttle.
But it wasn't knocking till like 3 minutes, and it started again. It's not tapping like, it's more like loud knocking, it's awful to ears.
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Islander
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PostPosted: 10:57 - 25 May 2016    Post subject: Reply with quote
Did you let the oil run low at any time? Have you identified which part of the engine the noise is coming from?
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Rogerborg
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PostPosted: 11:01 - 25 May 2016    Post subject: Re: Knocking after checking valves? Reply with quote
Actual knocking is bottom end, or conceivably piston slap.

Any chance we could see/hear a video?


Laamapalmu wrote:
I re-adjusted the valve clearance

Were they out? I'd go fairly hefty on the locknuts, they're on a lubed thread and subject to a lot of movement.

Laamapalmu wrote:
Cam chain and tensioner are ok. Neutral

Verified how?
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Laamapalmu
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Joined: 23 Dec 2015
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PostPosted: 11:28 - 25 May 2016    Post subject: Re: Knocking after checking valves? Reply with quote
Rogerborg wrote:
Actual knocking is bottom end, or conceivably piston slap.

Any chance we could see/hear a video?


Laamapalmu wrote:
I re-adjusted the valve clearance

Were they out? I'd go fairly hefty on the locknuts, they're on a lubed thread and subject to a lot of movement.

Laamapalmu wrote:
Cam chain and tensioner are ok. Neutral

Verified how?

Oil level hasn't been low, they have been out. Not a real verification but the chain is really thight, can't move it around with hand and it lifts the camshaft up when there isn't a camshaft cover on top. And the chain doesn't bend or anything.

Locknuts need more tension as they are lubed right? But 14Nm is already quite much, I'm not sure how big the bolt is... maybe around 6mm? And the nut is 10mm.

I don't have a video but it's like ticking. It's coming from top of the engine. Don't suspect piston slap as it's making the sound even when the engine is hot.
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Islander
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PostPosted: 11:33 - 25 May 2016    Post subject: Reply with quote
Ticking? Check your exhaust headers for leaks. Thumbs Up
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Meatybeaty
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PostPosted: 11:39 - 25 May 2016    Post subject: Reply with quote
Is this any good to you Thumbs Up
https://www.dropbox.com/s/62xz8u5cknavhwx/derbi%20125-250cc.pdf?dl=0
https://www.dropbox.com/s/03qxt8k5o45jzml/Derbi%20manual.pdf?dl=0
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Laamapalmu
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Joined: 23 Dec 2015
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PostPosted: 11:52 - 25 May 2016    Post subject: Reply with quote
Meatybeaty wrote:
Is this any good to you Thumbs Up
https://www.dropbox.com/s/62xz8u5cknavhwx/derbi%20125-250cc.pdf?dl=0
https://www.dropbox.com/s/03qxt8k5o45jzml/Derbi%20manual.pdf?dl=0

No sorry but I would be interested to know which Derbi site or from where did you get the manual? From finnish site I can get a manual but it's not a workshop manual.

Ticking from leaking headers, how is that possible? I shall check this.
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Meatybeaty
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PostPosted: 12:00 - 25 May 2016    Post subject: Reply with quote
Laamapalmu wrote:
Meatybeaty wrote:
Is this any good to you Thumbs Up
https://www.dropbox.com/s/62xz8u5cknavhwx/derbi%20125-250cc.pdf?dl=0
https://www.dropbox.com/s/03qxt8k5o45jzml/Derbi%20manual.pdf?dl=0

No sorry but I would be interested to know which Derbi site or from where did you get the manual? From finnish site I can get a manual but it's not a workshop manual.


Here
https://www.pdfmotomanual.com/ Thumbs Up
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Laamapalmu
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Joined: 23 Dec 2015
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PostPosted: 12:15 - 25 May 2016    Post subject: Reply with quote
I think it could be a constant piston slap due to too tight valve clearance. But I have to check it, and also check the exhaust. Thanks for helping, and the manuals are really useful! Mr. Green Thumbs Up
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Rogerborg
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Joined: 26 Oct 2010
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PostPosted: 13:32 - 25 May 2016    Post subject: Reply with quote
Laamapalmu wrote:
Ticking from leaking headers, how is that possible? I shall check this.

A small blow can indeed sound just like mechanical ticking, and can begin when the engine warms up and things expand - I've just had it on the Enfield.
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Ariel Badger
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PostPosted: 18:53 - 25 May 2016    Post subject: Reply with quote
Laamapalmu wrote:
I think it could be a constant piston slap due to too tight valve clearance.


Just how does that work?
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Ariel Badger
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PostPosted: 18:53 - 25 May 2016    Post subject: Reply with quote
Laamapalmu wrote:
I think it could be a constant piston slap due to too tight valve clearance.


Just how does that work?
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Laamapalmu
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PostPosted: 19:41 - 25 May 2016    Post subject: Reply with quote
Ariel Badger wrote:
Laamapalmu wrote:
I think it could be a constant piston slap due to too tight valve clearance.


Just how does that work?

I think its because the valve doesn't close completely, buuuuut that probably isn't the case because. The valve would come through the piston.
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Islander
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PostPosted: 20:39 - 25 May 2016    Post subject: Reply with quote
Laamapalmu wrote:


Just how does that work?

I think its because the valve doesn't close completely, buuuuut that probably isn't the case because. The valve would come through the piston.[/quote]

Piston slap is caused by the skirt of the piston hitting the cylinder wall and has nothing to do with valves. It's more common on two strokes.

What makes you think the valve isn't closing? If it's adjusted correctly then there's no reason it shouldn't close.

My advice to you is to stop looking for complicated causes to simple problems and start with the simple causes instead. Also make sure you describe problems accurately - there's a world of difference between a knocking noise and a ticking. As I said before, a slight leak at the header could easily cause the ticking noise you've described.
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Laamapalmu
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PostPosted: 09:07 - 26 May 2016    Post subject: Reply with quote
Islander wrote:

Piston slap is caused by the skirt of the piston hitting the cylinder wall and has nothing to do with valves. It's more common on two strokes.

What makes you think the valve isn't closing? If it's adjusted correctly then there's no reason it shouldn't close.

My advice to you is to stop looking for complicated causes to simple problems and start with the simple causes instead. Also make sure you describe problems accurately - there's a world of difference between a knocking noise and a ticking. As I said before, a slight leak at the header could easily cause the ticking noise you've described.

Oh alright. I'll have to buy a new gasket for the exhaust and check it. But the sound comes shortly after the engine has been started, so 5-15 seconds no ticking and after that it starts quietly. I suppouse this is the exhaust leakage and hope it's only that. Neutral
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pompousporcup...
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PostPosted: 09:23 - 26 May 2016    Post subject: Reply with quote
before you start with the exhaust, go back and double check your work.

If its ticking like mad and its present when the revs rise my guess is that you didn't get the clearances correct.

Either the clearance was accidentally set too high, ie too big of a gap and the ticking noise is the rocker bouncing up and down... OR you didnt tighten it enough and the nut has come loose with that gap now getting bigger.
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Islander
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PostPosted: 13:33 - 26 May 2016    Post subject: Reply with quote
Laamapalmu wrote:
Oh alright. I'll have to buy a new gasket for the exhaust and check it. But the sound comes shortly after the engine has been started, so 5-15 seconds no ticking and after that it starts quietly. I suppouse this is the exhaust leakage and hope it's only that. Neutral


You don't need to buy a gasket until you've checked it and ascertained whether or not there's actually a leak.
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Laamapalmu
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PostPosted: 19:33 - 01 Jun 2016    Post subject: Reply with quote
Islander wrote:
Laamapalmu wrote:
Oh alright. I'll have to buy a new gasket for the exhaust and check it. But the sound comes shortly after the engine has been started, so 5-15 seconds no ticking and after that it starts quietly. I suppouse this is the exhaust leakage and hope it's only that. Neutral


You don't need to buy a gasket until you've checked it and ascertained whether or not there's actually a leak.

I got an copper gasket for the exhaust. Still knocking, seems to come from the intake valve, no knocking when listening next to exhaust manifold, I have to check the clearane again.

Another nice problem is when I'm running rich but the exhaust valve is white and I have an side gapped spark plug.
https://i.imgur.com/iGDS9Mz.jpg
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A100man
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PostPosted: 22:51 - 01 Jun 2016    Post subject: Reply with quote
Perhaps an English lesson is needed for our Scandinavian cousin..

'Ticking' - is a low-volume medium-high pitch sound like you hear in a watch or clock.
'Knocking' -is a louder lower pitch sound like you hear with a door knocker or when you're big-end or main bearings are 'fucked'.

Perhaps your top-end is indeed knocking but that would tend to suggest a serious problem with the valve gear that cannot be adjusted out.
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