Sound advice please!

quadracer351

Coast to Coast
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!
https://youtu.be/uFeS2PduNdo

https://youtu.be/OJ0OupiX87Q

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Sounds like a valve hitting a piston, so check valve clearances first and eliminate that from the list of possible issues.
 
datadavid said:
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
 
Kamn said:
^^^ 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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quadracer351 said:
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*
 
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.
 
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.
 
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
66024ba83f50d254639cb115d5d4cee5.jpg


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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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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.
 
teazer said:
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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Tapping with the plug out
https://youtu.be/H82vGCoEXCc

No tapping plug in
https://youtu.be/Qs6PGYDiXT0

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Are the valves seated in their retainers at the top of the spring? I'd take the tappets completely out on those two valves and look for something loose. It still sounds like the tappets are clicking on top of the valve.
 
I can still hear it in the second video where you say "no tapping with plug in"
It definitely sounds like its coming from valve train........take it apart.
Who put this motor together?
 
Can you get a wrench on the crank bolt (with plugs removed) and rotate slowly until click happens then roll back a little and forward on the part of the cycle its happening at.....you will be able to pinpoint better.
Also, maybe have a friend do the rotating of the motor while you have a stethoscope on it
Id also drop the oil out and inspect for any metaly bits
 
Kamn said:
I can still hear it in the second video where you say "no tapping with plug in"
It definitely sounds like its coming from valve train........take it apart.
Who put this motor together?
Works Engineering in Brooklyn. Photo of what was found during rebuild and what was done
1fca544f796a146e6c771b5a87ae2db1.jpg
e3c2fbcf45f6a5a7136781dce145a8c5.jpg


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