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Author Topic: Sound advice please!  (Read 1923 times)

Offline quadracer351

  • Posts: 517
Sound advice please!
« on: Jun 14, 2017, 18:45:12 »
I know you guys hate trying to deduce engine problems from a video but I'm desperate before I keep having this thing run and possibly damage something. It's a 1974 cb750 first time starting on a  top end rebuild, bored it to 811 replaced cams, valves, springs, rockers and bench synched. I know it can be something as simple as a valve, a cam chain or effing just needing to be tuned. I just have a fear it's something that needs the motor removed again. Any advice to find the problem would be great!




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Offline teazer

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Re: Sound advice please!
« Reply #1 on: Jun 14, 2017, 19:42:26 »
Sounds like a valve hitting a piston, so check valve clearances first and eliminate that from the list of possible issues.

Offline datadavid

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Re: Sound advice please!
« Reply #2 on: Jun 15, 2017, 02:04:01 »
You dont want that sound from a newly rebuilt engine. Its scrap.

Offline quadracer351

  • Posts: 517
Re: Sound advice please!
« Reply #3 on: Jun 15, 2017, 03:56:51 »
You dont want that sound from a newly rebuilt engine. Its scrap.
Explain please

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Offline datadavid

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Re: Sound advice please!
« Reply #4 on: Jun 15, 2017, 04:18:33 »
Explain please

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Meaning dont run it until you found the cause!

Offline hillsy

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Re: Sound advice please!
« Reply #5 on: Jun 15, 2017, 09:41:32 »
Sounds like really loose tappets.

Offline Kamn

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Re: Sound advice please!
« Reply #6 on: Jun 15, 2017, 09:47:40 »
Meaning dont run it until you found the cause!

^^^ Exactly what he is saying
Don't run the motor anymore and I would take the valve cover off first and see if its coming from there, If you find nothing then remove motor and start opening it up to find the source
'82 Kawi GPZ550
'79 CX500 Cafe/Brat (in progress build)(took a break from it to.......)
'81 CX500 Custom (almost done)
'73 CB750 K3 (needs restoration)

Offline quadracer351

  • Posts: 517
Re: Sound advice please!
« Reply #7 on: Jun 15, 2017, 14:52:06 »
^^^ Exactly what he is saying
Don't run the motor anymore and I would take the valve cover off first and see if its coming from there, If you find nothing then remove motor and start opening it up to find the source
I have a bore camera on its way, it doesn't make the sound when its being kicked or turned over with no spark only when running. Think it's okay to run with the tapper covers off while I try to find it. Also don't know how much tension is on the cam chain, that can be a possibility too?

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Offline datadavid

  • Posts: 1044
Re: Sound advice please!
« Reply #8 on: Jun 15, 2017, 15:32:59 »
I have a bore camera on its way, it doesn't make the sound when its being kicked or turned over with no spark only when running. Think it's okay to run with the tapper covers off while I try to find it. Also don't know how much tension is on the cam chain, that can be a possibility too?

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Its probably not the cam chain, more likely a tappet come loose.
Two years ago i had a rotten camchain tensioner come loose on my girls bike on startup after i freshened up the valves and guides.
New valves and cam chain after that sound *shudder*

Online irk miller

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Re: Sound advice please!
« Reply #9 on: Jun 15, 2017, 15:58:18 »
You don't need to run it to find out if a tappet has come loose.  Pull the rotor cover, remove all 8 tappet covers and essentially go through the tappet adjustment procedure.  Check every single one for proper lash. 

Offline teazer

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Re: Sound advice please!
« Reply #10 on: Jun 15, 2017, 17:21:36 »
We all seem to agree that checking valve (tappet) clearance is the thing to do next.  When checking them, be really sure it is done at the right point in the cycle.  It's too easy to set them when the valves are open  (right time, wrong rotation) and end up with huge clearances.

Check one cylinder at a time at TDC on the firing stroke - not at TDC with both valves open or at half stroke or any other point.

Offline quadracer351

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Re: Sound advice please!
« Reply #11 on: Jun 16, 2017, 20:39:28 »
Could not find the two sets off feeler gauges i own have to pick up another set in the morning. I took the point cover off but it looks like the matching mark on the screw is misaligned

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Offline quadracer351

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Re: Sound advice please!
« Reply #12 on: Jun 19, 2017, 00:19:49 »
The valves all seem to be properly gapped and the cam chain tensioner tighten as described in the manual and I purchase a bore cam and everything inside the cylinder looks fine. I haven't started the bike up and had it running but turning it over by hand you can still hearing the ticking. It's very hard to tell if it's going from the cam or further down at this point.

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« Last Edit: Jun 19, 2017, 01:35:08 by quadracer351 »

Offline teazer

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Re: Sound advice please!
« Reply #13 on: Jun 19, 2017, 01:42:06 »
At what point is the noise happening?  - Just before Top dead center, just after?

With the valve covers off, turn it over by hand and see if you can tell which one it's coming from.


Offline quadracer351

  • Posts: 517
Re: Sound advice please!
« Reply #14 on: Jun 19, 2017, 14:02:03 »
At what point is the noise happening?  - Just before Top dead center, just after?

With the valve covers off, turn it over by hand and see if you can tell which one it's coming from.
Just spent twenty minutes trying to pin point when it happens. It sounds like it's coming from cylinder 4. Randomly I decided to cover the spark plug hole with my finger and turn it over a few times the sound wasn't there, put a plug in cylinder 4 and same thing, no tapping.

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