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Throttle-modulated rattle


SteveThackery

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SteveThackery

Friends and Countrypersons!

 

My NC doesn't sound like a normal Honda engine.  Instead of having a mechanically silent (or virtually silent) idle, there is some slight but noticeable mechanical noise, which I think would count as a rattle.

 

Interestingly, I've noticed that this rattle is modulated by the throttle opening - blipping the throttle makes it louder.  And yes, it's throttle-modulated rather than revs-modulated.

 

My first thought was that it is primary drive rattle due to the uneven firing interval - not at all unusual in bike engines.  However, I notice that it's exactly the same when driving along.  In these circumstances any play in the primary drive should be taken up, which makes me think it isn't coming from there.

 

I've read (on this forum, I think) that it could be the fuel injector noise.  I guess it's possible, but it would make it the loudest injector I've ever heard.

 

The only other time I've heard a rattle that is so accurately modulated by the throttle opening was due to piston slap in an air-cooled two stroke.  But ours in water-cooled and I wouldn't think the engine would have an unusually large piston-bore clearance.

 

I'm at a loss as to why the engine rattles at idle, and by what mechanism the throttle opening can make the rattle louder and quieter.

 

Any ideas?

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Guest bonekicker

Steve--Stop listening for engine noises--unless you have a utterly perfect engine running next to yours to compare--why should you think a noise is coming from??? or??? put some music on whilst riding-- very loud and you cant hear the engine noise--wind noise--road noise--farting noise any noise :console:

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Rocker66
50 minutes ago, bonekicker said:

Steve--Stop listening for engine noises--unless you have a utterly perfect engine running next to yours to compare--why should you think a noise is coming from??? or??? put some music on whilst riding-- very loud and you cant hear the engine noise--wind noise--road noise--farting noise any noise :console:

What a good idea ignore a noise and wait until it turns into something serious which is always a possibility although obviously not always. Always better to get a strange noise checked out and find it is nothing than to ignore it and it goes on to be something serious.

  • Like 1
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Guest Mac750

Valves out of adjustment, maybe a tad loose which is better than being tight. 

Grab a screw driver with a wooden handle and put the handle to your ear .

Not to listen to the engine with, I just like people poking things in ears. Someone once said "the only thing to stick in one's ear is one's elbow".  

👂😦👂👈

Edited by Mac750
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Rocker66
1 minute ago, Mac750 said:

Valves out of adjustment, maybe a tad loose which is better than being tight. 

Grab a screw driver with a wooden handle and put the handle to your ear .

Not to listen to the engine with, I just like people poking things in ears. Someone once said "the only thing to stick in one's ear is one's elbow".  👂😦👂👈

But sticking your elbow in somebody else's ear is an automatic red card😀😀

  • Like 3
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Guest bonekicker

No not saying--don't get engine checked over if something wrong--But when riders change bikes and get a NC the engine does sound rather different--and listening and trying to fadum out a unknown noise --without being able to compare--with a so called perfect engine noise--is a complete waste of time--it takes over the riders lives--and just--spoils the ridding pleasure--so why should we spend half our lives in the garage waiting to be told--that noise is quite normal--because that is precially what it is---a noisy strange engine--but that's one of the reasons we like about it--when it breaks--you will know straight away--there will be no noise--and when you twist the throttle--the engine will not respond---then take it to the garage--or ring Honda assist breakdown to take it :BangHead: 

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Rocker66
Just now, bonekicker said:

No not saying--don't get engine checked over if something wrong--But when riders change bikes and get a NC the engine does sound rather different--and listening and trying to fadum out a unknown noise --without being able to compare--with a so called perfect engine noise--is a complete waste of time--it takes over the riders lives--and just--spoils the ridding pleasure--so why should we spend half our lives in the garage waiting to be told--that noise is quite normal--because that is precially what it is---a noisy strange engine--but that's one of the reasons we like about it--when it breaks--you will know straight away--there will be no noise--and when you twist the throttle--the engine will not respond---then take it to the garage--or ring Honda assist breakdown to take it :BangHead: 

When it breaks it is too late. Better to get it checked if your not sure. At least it gives you peace of mind. I didn't say you had to get it checked at a garage anyway getting another NC owner to listen and see if it sounds the same as his/hers should be fine. If it doesn't then get a professional to check it. Prevention is better that cure and usually cheaper

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Tex

Steve, it may have been something I have written about injectors you're remembering? They most certainly can 'clack' quite badly and, interestingly, can vary between engines. 

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Tonyj

Doomed , turn the radio up and definitely Ignore it . If you don't acknowledge it , well it must be alright :0)

or do what rocker66 suggested. Btw it sounds really quite over the net .

  • Like 1
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Andy m
2 hours ago, SteveThackery said:

My NC doesn't sound like a normal Honda engine........... - not at all unusual in bike engines. 

 

The NC isn't a usual bike engine, its quite car like. If it runs well, gets decent MPG ( should be 70+ even if thrashed) and doesn't use any oil I'd go with the earplugs solution. Modern materials give the designers more options so every engine seems to have different noises. 

 

Mucking about with what isn't broken carries a risk of breaking it, so I always go with what I can measure rather than vauge hints. Its why I log my fuel use.

 

Andy

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SteveThackery

Thanks for all the comments, guys.

 

I should say that I'm not really worried about the noise, but more intrigued by it because not many rattles get worse when you open the throttle.  For instance, valve clearances make the same noise regardless of what you do with the throttle.

 

Do any of you folks think yours sounds a bit rattly?

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fred_jb

I found the NC engine quite noisy, especially on a neutral throttle, and likened it to the noise a coffee grinder makes - so not at all pleasant.  I noted the same thing on various YouTube videos featuring the NC, so I know it wasn't just my bike.  The only time I felt it sounded good was when giving it lots of throttle and accelerating hard, which I therefore did at every opportunity, which probably explains my poor mpg figures.  :D

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Andy m

I always thought you could hear the valve bits at idle. Not sure you would call it noisy.

 

Andy

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fred_jb
12 minutes ago, Andy m said:

I always thought you could hear the valve bits at idle. Not sure you would call it noisy.

 

Andy

I didn't always wear earplugs because I had managed to sort out the screen so that I had minimal wind noise.  As a result I was possibly more sensitive to engine noise, which when the engine was off-load seemed worse, like someone shaking ball bearings in a can, or one of those spray cans with a ball bearing inside that you have to shake to mix the paint, which might be a little more descriptive than the coffee grinder analogy.

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Guest Mac750

Quick thought when it rattles on tick over pull the clutch lever in whilst the bike is not in gear. With the lever in does it go away. If so that's normal "they all do that sir ".  Hard to diagnose a noise on a screen but we can try 😀

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embee

They are quite rattly/clattery, I genuinely think "they're all like that, Sir". I run mine on 50/50 mix of 10W30 and 10W40 oil (Castrol Power1) and I reckon it's a little quieter than on the straight 10W30. It's definitely quieter when cold, whenever I start it cold I think it sounds very nice, but then when hot it clatters a bit.

 

Piston noise is certainly highly sensitive to throttle (load) at very light loads and idle. I spent a lot of time doing piston development on various engines, rattle at idle or just off idle was quite tricky to get right, the pin offset is the critical issue usually. The gudgeon pin is offset towards the thrust side of the piston by 1-1.5mm typically, depending on bore size and combustion characteristics. This is used to remove the piston tilt before the firing pressure does it, if you can get it biased to one side before the firing it doesn't then "clack" as much as it moves across the bore. Pistons usually change attitude (tilt and which side of the bore they touch) up to half a dozen times during a cycle as inertia, gas pressure, and friction loads vary.

I rather suspect this is what we are hearing in the NC engines.

From Google images ......

833800.jpg

 

Interestingly the DCT has a split gear with spring loading (items 3.4.5) on the primary gear on the crank to cut down the rattle you can get especially with the uneven firing, but the manual bikes don't have this. Presumably the inertia of the DCT clutches is much greater than the manual clutch assembly so influences it. The DCT clutch assembly is a meaty big lump by the way. I had mine out when replacing the shifter drum pin. It's not intended to break!

From https://www.bike-parts-honda.com/pieces-honda-detail-71541-71541-NC750XDE-2015-E_7_1-NC+750+X+ABS+DCT.html

E_7_1.jpg

Edited by embee
  • Like 2
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Guest Mac750

MZ 250 on tick over on the main stand, ringtingshackalacalacalaclac,

Wasn't your bike parked on that side of the car park earlier ? 🤔

 

Yes but it likes to dance. 😁

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Mike5100
20 hours ago, bonekicker said:

Steve--Stop listening for engine noises--unless you have a utterly perfect engine running next to yours to compare--why should you think a noise is coming from??? or??? put some music on whilst riding-- very loud and you cant hear the engine noise--wind noise--road noise--farting noise any noise :console:

I was at first going to have a go at bonekicker for 'patronising' you Steve but then decided not to 😀😀. Because there is something in what he says - I'm terrified of all the noises that my bikes make if I ride them without my usual earplugs

 But it goes deeper than the sound. If it doesn't sound right then it may also be not vibrating right either. To give an example   My Rocket3 annoyed me intensely at tootling speeds because it seemed to have a hesitation and surging at low revs which I put down to Euro 3 compliance because I had had the triumph dealer check most things including. Throttle body balance which I had paid £100 for. A couple of months ago I paid a mobile triumph engineer £20 to do the TBs again. And now it's magic and I'm smiling when tootling. 

The moral  being that if an engine issue bothers you then try and get it sorted - it is worth it to some of us

(by the way the Africa twin is also clattery and noisy at idle)

mike

Edited by Mike5100
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Tex

My Integra sounded like two skeletons shagging in a metal box. But it flew! So I never worried about it.. :)

  • Like 6
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Guest bonekicker

Steve in no way was I patronising you or anyone--- has any working person got the spare time to keep going into the workshop and keep asking --do you think that's a weird noise?? time and time again--we buy a bike either new or second hand--we have a warranty--so if anything goes wrong they will fix it--they wont fix--what you think is a weird noise---and like I did say--without another ideal perfect engine running at the side of you --to gain what is a normal noise and what is not a normal noise--you nor I--nor the workshop can tell.---I cant think of another way to explain it. :thumbsup:

 

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Rocker66
11 minutes ago, bonekicker said:

Steve in no way was I patronising you or anyone--- has any working person got the spare time to keep going into the workshop and keep asking --do you think that's a weird noise?? time and time again--we buy a bike either new or second hand--we have a warranty--so if anything goes wrong they will fix it--they wont fix--what you think is a weird noise---and like I did say--without another ideal perfect engine running at the side of you --to gain what is a normal noise and what is not a normal noise--you nor I--nor the workshop can tell.---I cant think of another way to explain it. :thumbsup:

 

Great if you never ride far from home but who wants a bike to breakdown in the middle of nowhere which could happen. Nobody is aying you need to go to the garage constantly as you are hardly likely to get different worrying noises on a regular basis. As I said you only need a person with a similar model to listen to see if it sounds the same as theirs. That cost nothing. Any decent dealer will listen and tell you if their is something wrong or not without charging. You shouldn't need to make an appointment for this and could do so when you are in for a service or just passing  at your convenience. As to warranty if you buy privately you don't have one.

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bazza
On 01/05/2017 at 15:53, SteveThackery said:

Friends and Countrypersons!

 

My NC doesn't sound like a normal Honda engine.  Instead of having a mechanically silent (or virtually silent) idle, there is some slight but noticeable mechanical noise, which I think would count as a rattle.

 

Interestingly, I've noticed that this rattle is modulated by the throttle opening - blipping the throttle makes it louder.  And yes, it's throttle-modulated rather than revs-modulated.

 

My first thought was that it is primary drive rattle due to the uneven firing interval - not at all unusual in bike engines.  However, I notice that it's exactly the same when driving along.  In these circumstances any play in the primary drive should be taken up, which makes me think it isn't coming from there.

 

I've read (on this forum, I think) that it could be the fuel injector noise.  I guess it's possible, but it would make it the loudest injector I've ever heard.

 

The only other time I've heard a rattle that is so accurately modulated by the throttle opening was due to piston slap in an air-cooled two stroke.  But ours in water-cooled and I wouldn't think the engine would have an unusually large piston-bore clearance.

 

I'm at a loss as to why the engine rattles at idle, and by what mechanism the throttle opening can make the rattle louder and quieter.

 

Any ideas?

maybe try that stuff recommended to quiet it down -MX1 i think its called?. Didn't they use sawdust in axles 100 years ago for the same reason?

  • Like 2
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bazza
23 hours ago, Rocker66 said:

What a good idea ignore a noise and wait until it turns into something serious which is always a possibility although obviously not always. Always better to get a strange noise checked out and find it is nothing than to ignore it and it goes on to be something serious.

Yes but whats a bad noise to one owner isnt a noise at all to another Rocker. I think that listening to the same model of bike owned by another is the way to go - plus you can learn a lot about other things. If the bike is properly serviced it could be just a one off - we can get awfully worried about little things!

bet you spent hours discussing cam lift etc when the BSA was your steed of choice!

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Rocker66
4 minutes ago, bazza said:

Yes but whats a bad noise to one owner isnt a noise at all to another Rocker. I think that listening to the same model of bike owned by another is the way to go - plus you can learn a lot about other things. If the bike is properly serviced it could be just a one off - we can get awfully worried about little things!

bet you spent hours discussing cam lift etc when the BSA was your steed of choice!

If you check out my posts on this thread you will find that is exactly one of things I suggest.

what I don't think is a good idea is ignoring it

  • Like 1
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