1978 cb550 rattle under load. Any help?

Howdy good folks. I hate to be one of those people who just come here to ask for help without being able to reciprocate, but I'm coming to my whits, and knowledge's end. I'm having a baffling issue with my bike. Under load, often from a stop or while already in motion, from 2800 - 3200 rpm or so I get a rapping/rattling that goes away as the speed increases and load decreases from what seems like the upper area of the motor.
.. Edit...
I neglected to mention that it happens only at operating temperature. So far.

It's a completely stock bike set up (as far as I know).
--Carbs have been cleaned, bench and briefly vacuum synced before an intake leak caused issues then fixed. It idles fine enough around 1100 rpm after it warms up now. They were inspected for proper slow jets and float level. I haven't found an intake vacuum leak as of yet.
--Cam chain has been adjusted, still noisy. Fresh oil change with 20/50 motorcycle oil for fear of oil starvation at the top end, still noisy. Valves have been adjusted twice.
--Spark plugs are Champion equivalent of D7EA. NGK on the way.
--I put in a blend of 94ish octane gas, still noisy.
--The drive chain has been adjusted to spec, still noisy.
My unknowns at this point are the carb needles, size, taper and clip settings, engine internals as in pistons or upgraded cam. It has a Martek electronic ignition which I finally got to checking.
--The initial timing seemed to be set waaaaaay advanced, about 10 - 15 degrees. I have a video of just after a small adjustment then after timing was set to what I hope is spec at idle. The advance mechanism is also working when I checked it. Still noisy. :'( :'(
I was told that the PO had "raced" this bike at some point and gave me 1/8 mile times and such babble.
I've scoured the internets for honda cb engine noises similar to what I'm getting but it's all cam chain this and clutch rattle that, nothing like what I've got. Before tearing this thing open and dropping a bunch of money, I'd like to know if any of you can give me a direction or better diagnostic methods for identifying and repairing. I was able to record said noise and hopefully it's good enough quality.
I'm afraid of it being the primary chain hitting the case, I haven't yet dropped the pan for inspection. I also suspect the cam cover and rockers, maybe a bad spring.

I hope and pray that any of you can help. Thank you a million times and may you have many beautiful and masculine children.

http://youtu.be/aeypOaEaYC0 Rattling noise 1

http://youtu.be/7Ha_hT-Wo5s Rattling noise 2

http://youtu.be/3t4kqG--RNE Timing after slight adjustment

http://youtu.be/eA-QCm8-CD4 Timing at final setting

Your videos are set to private....
Could possibly be your cam chain or primary chain. Cam chain might be stretched beyond being able to be adjusted.
Primary chain could be rubbing on the cases. If it has been raced, and the chain hasn't been replaced, could be a likelihood the chain has had a rough time of it and been stretched.

Privacy settings fixed. Thanks for the input. I'm going for pin point diagnosis if I can. I would need to drop the pan and remove exhaust to get to it. I'd like to keep the tear down to a minimum until absolutely needed. But it seems to be upper end to me could be lower because of my limited access when riding and recording.

you can check the slack in the primary chain and cam chain both without too much work at all

sounds like cam chain

Loose valve or cam chain.

I appreciate the responses guys.
In all my searches for this, cam chain noise been prevalent at idle without needing to rev or load it up at any speed. On the last can chain adjustment there was about 1/4", or just under, of the threaded bolt exposed. I've seen no specs on how far it's able to go.
I suppose it could still be a cam chain issue if it's reached the end of it's adjustability.
I was hoping it was the timing because it was so off and it seemed to have alleviated it. Wishful thinking I guess.
I suppose this week I'll have to look into it deeper and get a more thorough list of what to look for, adjust, or change.
Any other ideas?

How are you adjusting the cam chain? Have you been doing as described in the service manual?

Yessir. Everything according to the shop manual, Chilton manual, and I even ponied up for the Clymer manual to reduce the chance of discrepancy. I'll be doing it again soon just in case. Maybe turning the bolt a bit to make sure it's got tension. The only thing is when I loosen the nut and the bolt moves inward with tension, when I tighten it up while pressing slightly on the bolt with the flathead, the nut just pulls it outward then locks down in the same previous area as if nothing was done. Shouldn't the tension keep it pulled inward to help it lock down? Or is it backwards from what I'm thinking how it works? More research for me.
Have these been know to develop valve float or bad springs in stock engines?
This is either something very common that I'm overthinking or something just out of my knowledge range.

I hear the cam chain rattle, but those motors have notoriously noisy cam chains. But I also hear what sounds like an exhaust leak when you get on the gas....but I could be hearing intake noise from pods, if you have them installed.

Hard to tell in a video.

if the cam chain is running slack(something worn out or chain stretched stuck tensioner etc) you should be able to feel and see it by gentle rocking the crank back and forth a few degrees with a wrench then look in at the rocker arms watch for delays in motion
with a properly tensioned chain there will be zero lag

ceebeehead said:

Yessir. Everything according to the shop manual, Chilton manual, and I even ponied up for the Clymer manual to reduce the chance of discrepancy. I'll be doing it again soon just in case. Maybe turning the bolt a bit to make sure it's got tension. The only thing is when I loosen the nut and the bolt moves inward with tension, when I tighten it up while pressing slightly on the bolt with the flathead, the nut just pulls it outward then locks down in the same previous area as if nothing was done. Shouldn't the tension keep it pulled inward to help it lock down? Or is it backwards from what I'm thinking how it works? More research for me.
Have these been know to develop valve float or bad springs in stock engines?
This is either something very common that I'm overthinking or something just out of my knowledge range.

Click to expand...

Not sure I understand what you're saying here. The tensioner automatically sets itself, once you undo the nut. If you turn the screw clockwise, it takes tension off the chain, let it go, and it goes back into tension. Don't try to turn it counter clockwise.
So all you gotta do is back the nut off, turn the screw and let it return itself, then lock the nut, whilst holding the screw from turning.
All this has to be done with cylinder 1&4 at 15 degree ATDC.
If you already know a this and have done so, disregard.

If you still think its cam chain related, your cam chain might be stretched, and your guides might need looking at.

I had a 78 550k with a mystery rattle, that later turned out to be a loose clutch basket. That particular noise only showed up NOT under load, and at and around idle, went away above 2000 rpm.

If it helps you at all, mine didnt sound at all like your rattle. I'm leaning to exhaust leak, or cam chain stretch. <<< sheer guesses tho.

Awesome stuff. It prompted me to do another inspection tonight of the chain tensioner. Per the manual, set the timing to about 15 degrees and loosen the lock nut. BUT!!...
As I look for more info I see that the bolt should turn in on its own after the lock nut is loosened? It shouldn't move in or out unless bad things? I took a little video of what I'm hoping isn't an issue, but my luck sucks.

http://youtu.be/tPC9jJbOcLU

Worst case scenario, the cam or somesuch in the tensioner is crapped and I want to die.
Opinions?

Looks normal to me, its the same on mine atleast.

I checked it out again today before getting dark. I checked the tensioner operation and it seems good. I turned the bolt clockwise and it returns, counter clockwise it has less movement as it's already taut against the chain. I turned the crank nut and watched the valves move up and down without any delay, so the chain isn't slack. I turned the tensioner bolt a bit and tightened it up then went for a ride, still noisy.
Aside from the noise, this engine runs strong and pulls great. Then again I have no basis for comparison except for the automobile engines I've done.
I pulled the plugs and they look good and a slight mocha tan, the ceramic has a light red color, but that might be the additives I added.
I rechecked timing and it's spot on at idle and advances properly up to 3000 rpm, so that hasn't moved since I've fiddled.
I'm leaning towards mechanical at this point. I'm still trying to use the fact that it only happens when it gets warmed up as a diagnostic clue. Properly fuel atomization causing a proper burn thus more power and impact on the pistons, rod, crank and bearings?
I tried to give it a go on the center stand in second gear then loading it up, but I didn't have much luck. Maybe 3rd or higher gear? I would make diagnosis a billion times easier if this damn thing would make that noise while stationary.
If I have the free time this weekend I'll try to remove the valve cover if possible, maybe even drop the pan to check the primary chain for any slack.

Things I need to think about, the temperature issue, and what if the rattle is low in the engine and just sounds higher, like transmission or something that runs on oil pressure.

Next part in my continuing saga of failure.
On the thought that I was actually using gas that was too high of an octane causing overheating I put some 87. No change.

The spark plugs!!! In fact when I took a better look appear to be overheating. I'll try attaching a pic. They're a bit flaky yellow on the electrode and it makes sense due to when this issue occurs.
So timing is on, fuel is proper quality, stock intake and exhaust setup, I haven't found an intake vacuum leak. I'm doing a compression test tomorrow. I think I'll be checking for proper upper end oiling also. AAAARRRRRGGGGHHH!

That plug looks really lean. Maybe too much advance causing preignition. That would cause a rattle. Using the high octane fuel usually helps the issue.

that plug is fine not lean at all

the noise is cam chain plane as day

Cam chain tensioner of my '78 CB550K http://youtu.be/XMv7waOW98Y

Disclaimer: I didn't put my motor at 15° 1-4 TDC. Don't think it'll matter too much, though. I think your tensioner is crapped and you want to die. But seriously, I hear you can replace that with the motor in. But, just so you know, I took my motor out with a buddy in about an hour and a half. Not hard at all. Only thing is that the tensioner could run you upwards of $200 or more. And they're hard to find. But check out https://www.davidsilverspares.com/CB550K-1978-USA/


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1978 Honda CB550K