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2006 VN750
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Discussion Starter · #1 ·
What the hell is this intermittent rattling noise? Does this when idling. Sounds more internal than anything. Nothing external is loose or rattling.

(I tried to embed the video here, but this site doesn't permit "shorts" from YouTube.)

Thanks!
 

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Sounds like an intermittent jack hammer thats very far away. How many miles are on the bike? From my own experience and research I've seen that the ACCT's usually need to be replaced between 15k and 25k +/-. I was at 26k when mine started making very very slight noises, so I just changed them out for the MCCT's. But this is a sound I've never heard before on a Vulcan or any other ICE for that matter.
 

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2006 VN750
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Discussion Starter · #5 ·
Sounds like an intermittent jack hammer thats very far away. How many miles are on the bike? From my own experience and research I've seen that the ACCT's usually need to be replaced between 15k and 25k +/-. I was at 26k when mine started making very very slight noises, so I just changed them out for the MCCT's. But this is a sound I've never heard before on a Vulcan or any other ICE for that matter.
There's not quite 10k on it. When I bought it about a year ago, it had 8500 miles and I've added about a thousand miles to that. Without looking at the odometer, I think it's at 9400-ish.

And this sound is brand new. Just started doing it the last few times I've cranked it and let it idle. Never heard it before. I placed my gloved hands all over the engine and couldn't feel any additional vibration occuring at the same time as that sound.

I've noticed nothing different when riding. I'm clueless....
 

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2003 VN750
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Does sound like a rocker arm, like maybe a lifter bleeds off a bit, briefly, or a valve is getting sticky. Seafoam in the oil can free sticky lifters and valves.

It's not a spark plug wire arcing, is it? Sounds more metallic I think.
 

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2006 VN750
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Discussion Starter · #8 ·
Does sound like a rocker arm, like maybe a lifter bleeds off a bit, briefly, or a valve is getting sticky. Seafoam in the oil can free sticky lifters and valves.

It's not a spark plug wire arcing, is it? Sounds more metallic I think.
I'm inclined to think that if it were a spark plug wire arcing, it would be affecting the running of the engine. I saw no fluctuation or noticeable irregularities in the rpm gauge.

I don't know if I'm connecting invisible dots, but it seems like this has only begun once the weather became colder.

I've also noticed that if I ride around for a few minutes, and then park it again and let it resume idling, it seems to disappear.

Definitely something I've never encountered before.
 

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2003 VN750
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I'm inclined to think that if it were a spark plug wire arcing, it would be affecting the running of the engine. I saw no fluctuation or noticeable irregularities in the rpm gauge.

I don't know if I'm connecting invisible dots, but it seems like this has only begun once the weather became colder.

I've also noticed that if I ride around for a few minutes, and then park it again and let it resume idling, it seems to disappear.

Definitely something I've never encountered before.
Since it has two spark plugs per cylinder, you wouldn't see much change if one is arcing, mine didn't change when it was arcing.

Probably a gummy valve stem slowing the valve movement, when it gets slow to close, the tapping happens. After warmup there's more clearance so it's able to close properly.
 

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I’ve posted this plenty of times. Here is a text book failing ACCT to compare but they sound different to me.
They sound different to me as well. However the OP's engine sounds like it is running at a bit faster RPM than the 2nd example. The last one is the sound I recognize as it clearly is RPM related. The 1st engine sounds really fast and I also think it sounds a little electrical in nature. ( Like a set of contacts opening and closing real fast, but I do not understand how it could be electrical but not effect how the bike doesn't miss while it is running.


The odd rhythm has me a bit confused as none of the ACCT's I have replaced (4 total - 1 at a time) ever made a real rapid series of taps (or clicks) then stopped completely and then did it again. Rather, like the second video the chains rattled in time to the rest of the timing events, speeding up or slowing down, in the same rhythm of the engine's RPMs. After the motors were warmed up the ACCT noise was not as bad but it was still there. However when the engine was warmed up the ACCTs would only knock about half as long. Occasionally the knocking would actually stop intermittently, even while just idling if the engine was completely warmed up. When riding every day it often would not make any noise if starting and stopping frequently.
 

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How cold?
I never try monitoring engine sounds until it’s warmed up.
You can usually find plug wire arcing by starting it up in a dark place. The right side plug wire has been known to arc on the front cylinder head. Re-routing the wire is all that’s needed.
 

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They sound different to me as well. However the OP's engine sounds like it is running at a bit faster RPM than the 2nd example. The last one is the sound I recognize as it clearly is RPM related. The 1st engine sounds really fast and I also think it sounds a little electrical in nature. ( Like a set of contacts opening and closing real fast, but I do not understand how it could be electrical but not effect how the bike doesn't miss while it is running.


The odd rhythm has me a bit confused as none of the ACCT's I have replaced (4 total - 1 at a time) ever made a real rapid series of taps (or clicks) then stopped completely and then did it again. Rather, like the second video the chains rattled in time to the rest of the timing events, speeding up or slowing down, in the same rhythm of the engine's RPMs. After the motors were warmed up the ACCT noise was not as bad but it was still there. However when the engine was warmed up the ACCTs would only knock about half as long. Occasionally the knocking would actually stop intermittently, even while just idling if the engine was completely warmed up. When riding every day it often would not make any noise if starting and stopping frequently.
The bike in the second video is mine, and you’re spot on, that was recorded when the bike was sitting all day outside work and I just started it up. It would make the noise and it would fade in a few minutes but in a couple weeks time it started taking a lot longer to quiet down and that’s when I switched them out.
 

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2006 VN750
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Discussion Starter · #13 ·
@Spockster @Green1 @Knifemaker @mmart @Vulcan_Frank_750 :

Thanks y'all for the info and suggestions. Because the weather is still too cold for riding (well, for me), I'll check a few things that I can when she's idling, and I'll try to make note of everything I observe.

From what I'm gathering from everyone, it's nothing to be seriously alarmed about. Yet.

I wish I'd win the lottery, because then I'd just buy a dozen or so motorcycles and hire my own private mechanic to maintain them. I don't mind turning a wrench when I need to, but I'd prefer not to need to! :southpark:
 

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Ominous - unfortunately nothing to add to the (technical) discussion here - but I saw the same thing with the Youtube "shorts" not being able to be embedded in this forum.
One way to get around it, find the URL for your short (using my video as an example)
h ttps://www.youtube.com/shorts/jlzjulAjmLk
Replace the text "shorts/" in the URL with "watch?v=".
This will render it as a regular YouTube video, and this resulting URL you can then copy/paste into our forum's text box.

Phew. Bit of a chore. But that'll get it to show up.

YouTube looks to be leaning really hard into the the whole "shorts" thing, probably to compete with TikTok for kids' attention.
 

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2006 VN750
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Discussion Starter · #15 ·
Ominous - unfortunately nothing to add to the (technical) discussion here - but I saw the same thing with the Youtube "shorts" not being able to be embedded in this forum.
One way to get around it, find the URL for your short (using my video as an example)
h ttps://www.youtube.com/shorts/jlzjulAjmLk
Replace the text "shorts/" in the URL with "watch?v=".
This will render it as a regular YouTube video, and this resulting URL you can then copy/paste into our forum's text box.

Phew. Bit of a chore. But that'll get it to show up.

YouTube looks to be leaning really hard into the the whole "shorts" thing, probably to compete with TikTok for kids' attention.
Great tip! And TikTok should be destroyed with fire. Just my 2 cents 😂
 

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Just to add my 2 cents, If you haven't already, I would change the oil/filter and check you have good oil pressure. It may be something with the hydraulic lash adjusters which require good oil pressure to operate. There is also an oil screen at the bottom of the case that can be checked for blockage in addition to the filter. Finally there is a little screen in the heads themselves that feeds the HLA's that may need to be cleaned. If it is cold out may try a different viscosity oil and of course, make sure it is good and warmed up.
 

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2006 VN750
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Discussion Starter · #17 ·
Just to add my 2 cents, If you haven't already, I would change the oil/filter and check you have good oil pressure. It may be something with the hydraulic lash adjusters which require good oil pressure to operate. There is also an oil screen at the bottom of the case that can be checked for blockage in addition to the filter. Finally there is a little screen in the heads themselves that feeds the HLA's that may need to be cleaned. If it is cold out may try a different viscosity oil and of course, make sure it is good and warmed up.
Will do, thanks!
 

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To jump in here, at risk of repeating what's been said, I vote for a failing ACCT.
I bought my 2005 with ~8000 on it and it started failing around 11k.
The consensus is around 17-25k, but I think when a bike is low mileage, they go early.
Below is my video. This was a cold start. At 3 minutes, it suddenly stopped but would return when I revved up.
It started making the noise on cold starts during a multi-day trip but it would go away when the bike warmed up.
Each day, it took longer to go away.

Try the Grumbo Trick to see if the noise goes away. That will tell you right away if it's the ACCT or not.

 

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2003 VN750
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To jump in here, at risk of repeating what's been said, I vote for a failing ACCT.
I bought my 2005 with ~8000 on it and it started failing around 11k.
The consensus is around 17-25k, but I think when a bike is low mileage, they go early.
Below is my video. This was a cold start. At 3 minutes, it suddenly stopped but would return when I revved up.
It started making the noise on cold starts during a multi-day trip but it would go away when the bike warmed up.
Each day, it took longer to go away.

Try the Grumbo Trick to see if the noise goes away. That will tell you right away if it's the ACCT or not.

Wow, that tapping did just shut completely off at 3 minutes. Has a similar rhythm and speed as Omi's.

I think whatever it is, it not bad enough to worry about yet, but I would monitor it.

My acct taps lightly on cold start, but is gone after warmup, It's been like that for at least three years. It's not as bad as Jason's, but steady and louder than Omi's.

So thinking about Jason's noise, it came back after he blipped the throttle, I wonder if the acct plunger shaft gets sticky,. A chain or belt will tighten/loosen as the power changes. So his finally quiets down, then when he revs it the plunger gets pushed back by the chain. Certainly a weakness in the spring, but a sticky plunger explains it being able to recover and stop tapping again. The spring couldn't regain tension.

So many people have reported no help by installing new springs. They aren't going bad?

Oil gets through the acct, and so follows varnish. I didn't pay attention to the tapping after I ran Seafoam in the oil. I'll try to listen on the next start-up.
 

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2006 VN750
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Discussion Starter · #20 ·
To jump in here, at risk of repeating what's been said, I vote for a failing ACCT.
I bought my 2005 with ~8000 on it and it started failing around 11k.
The consensus is around 17-25k, but I think when a bike is low mileage, they go early.
Below is my video. This was a cold start. At 3 minutes, it suddenly stopped but would return when I revved up.
It started making the noise on cold starts during a multi-day trip but it would go away when the bike warmed up.
Each day, it took longer to go away.

Try the Grumbo Trick to see if the noise goes away. That will tell you right away if it's the ACCT or not.

Wow, that tapping did just shut completely off at 3 minutes. Has a similar rhythm and speed as Omi's.

I think whatever it is, it not bad enough to worry about yet, but I would monitor it.

My acct taps lightly on cold start, but is gone after warmup, It's been like that for at least three years. It's not as bad as Jason's, but steady and louder than Omi's.

So thinking about Jason's noise, it came back after he blipped the throttle, I wonder if the acct plunger shaft gets sticky,. A chain or belt will tighten/loosen as the power changes. So his finally quiets down, then when he revs it the plunger gets pushed back by the chain. Certainly a weakness in the spring, but a sticky plunger explains it being able to recover and stop tapping again. The spring couldn't regain tension.

So many people have reported no help by installing new springs. They aren't going bad?

Oil gets through the acct, and so follows varnish. I didn't pay attention to the tapping after I ran Seafoam in the oil. I'll try to listen on the next start-up.
Excellent advice from you both, thank you! I've read and bookmarked the Grambo trick page for easy reference later.

So, let me add some details that might be relevant or might not:

  • Once I reinstalled the cleaned and rebuilt carbs, I performed an oil change. However, I was unaware of the internal filter and only changed the external filter. Now aware of that internal filter, I will be performing another oil change once the weather cooperates. (No garage yet, but she's covered with a large heavy blanket, then two new tarps, and finally a bike cover.)
  • I've been cranking the bike up at least once per week. The sound is recent. Probably only began within the last three or four idling sessions.
  • At the end of each ride/idling session, I've been making it a habit to close the petcock and allowing the bike to idle until it burns through the fuel in the carbs. That sound definitely weakens and usually disappears after she's plenty warm.
  • If this sound is indeed the ACCT, then I'm actually relieved. At just under 10k miles, I'd rather not have major engine problems.

Once again, thanks for the info and advice, fellas!
 
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