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Author Topic: 1978 CB750K Whining?  (Read 1936 times)

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Offline zeus87

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1978 CB750K Whining?
« on: August 26, 2008, 11:40:55 PM »
36,000 miles, all tuned, runs awesome.  530 chain conversion, new clutch.  Anway, ive noticed the bike whines a little when accelerating it seems like its 2nd 3rd maybe 4th.  It is coming from the chain side of the bike.  I really noticed it when i let a friend take it for a ride, and listened to her pull away.  Any ideas?
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Offline pdxPope

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Re: 1978 CB750K Whining?
« Reply #1 on: August 27, 2008, 12:07:02 AM »

Bad wheel bearing?
Just what do you mean "530 chain conversion"??

Does the noise rise & fall with engine RPM or with the speed of the bike. Does it do it in gear or when coasting or both?

Put it up on the centerstand & run it through the gears. This should give you a controlled environment to do a little diagnosis. Just be carefull it doesn't fall off the stand at 4500 in 4th gear! :o  :D


-JP


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Offline hcritz

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Re: 1978 CB750K Whining?
« Reply #2 on: August 27, 2008, 08:05:24 AM »
Hey Zeus...
I have a 77 and it does the same thing...Had 9,000 miles on it when I got it...hasn't gotten any worse at 20,000. Mine is loudest in third under accel...
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eldar

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Re: 1978 CB750K Whining?
« Reply #3 on: August 27, 2008, 08:56:54 AM »
I seem to have something like that too. Kinda of a low howl. But only at lower rpm. If I am really getting on it, does not happen, at least not that I can hear.
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Offline 754

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Re: 1978 CB750K Whining?
« Reply #4 on: August 27, 2008, 09:39:49 PM »
They are the FINEST... :o

Suck it up & deal with it... ;)
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eldar

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Re: 1978 CB750K Whining?
« Reply #5 on: August 28, 2008, 06:07:16 AM »
754, that is what is happening. The air is being sucked in the way it should have been on the old heap 750s!
Better performance then the 72-76, yeah I can deal.
Or should I say equal to the 69? Since mags that tested the 69 also did the 77/78 models.
Oh but that couldnt happen cause you dont want it to. And yet the 78 engine is the engine of choice for serious engines.
« Last Edit: August 28, 2008, 06:08:55 AM by eldar, Master of the K8 Thunder! »
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Hendey

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Re: 1978 CB750K Whining?
« Reply #6 on: August 28, 2008, 06:21:37 AM »
My 1978 CB750F with 12,000 miles sounds like a cement mixer.

Have never been able to narrow it down. Hasn't gotten any worse over the years.
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Offline zeus87

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Re: 1978 CB750K Whining?
« Reply #7 on: August 28, 2008, 11:34:50 PM »
sorry about the delay, was out of town.  It is under acceleration only, by 530 chain conversion i mean it was a 630 (factory) and it was replaced with a 530 chain/sprockets. 
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Offline Hush

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Re: 1978 CB750K Whining?
« Reply #8 on: August 29, 2008, 01:01:30 AM »
I'm with the guy who owns a cement mixer, I mean like with all the undiagnosed rattles bangs and pops my bike makes do I really need you to find something else for me to worry about? ;D
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Offline pdxPope

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Re: 1978 CB750K Whining?
« Reply #9 on: August 29, 2008, 01:11:49 AM »

Well, from the sounds of it, the noise may be a typical thing. (Although I find it hard to believe that Honda let them roll out of the factory like that.)

I would still try some controlled experiments to help narrow the area down.


-JP


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eldar

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Re: 1978 CB750K Whining?
« Reply #10 on: August 29, 2008, 06:12:37 AM »
Well being only under accel, the only thing really affected is air intake. I mean, speed is speed and so I do not think it is speed related. I think it is the added air being sucked into the engine.
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Offline BobbyR

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Re: 1978 CB750K Whining?
« Reply #11 on: August 29, 2008, 06:20:38 AM »
I have the same thing on my 78K. I think it is normal. It is kind of a turbine sound that comes out at mild acceleration. I think it may be the gearbox or timing chain.
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Offline pampadori

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Re: 1978 CB750K Whining?
« Reply #12 on: August 29, 2008, 07:56:04 AM »
noise is from the dog gears meshing. its normal.  sometimes a different oil will change the sound.  but not something to worry about.
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eldar

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Re: 1978 CB750K Whining?
« Reply #13 on: August 29, 2008, 09:30:12 AM »
That is EXACTLY the sound I get. I think it sounds pretty cool.
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Offline taxiscooter

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Re: 1978 CB750K Whining?
« Reply #14 on: August 31, 2008, 03:27:45 PM »
Sounds like we have a similar problem. My 750k7 whines in 4th and 5th. See my post under 4th and 5th gear whine on aug 30th.
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Offline rbmgf7

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Re: 1978 CB750K Whining?
« Reply #15 on: August 31, 2008, 03:38:56 PM »
mine has an oscillation to it when in low rpm, doesn't matter what gear it's in. can hear it mostly in decceleration. i'm thinking it's the wheel bearings because now it's starting to clunk at low speeds.
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