I am out of ideas guys and I hate myself for not parting with her before I started investements. What was done

1. New camchain, new camchain guides, new self-locking camchain tensioner - absolutely no chance of any camchain play.

The picutres of the tensioner here:
https://cbrforum.com/forum/how-tos-8...-153270/page2/

2. New alternator chain, the guides inspected - ok

3. New oil pump chain - the guide inspected - ok

5. the carbs cleaned, two sets of carbs tested, runs a smooth as I can only adjust them - a lot of time invested.

6. the Stick Coils installed today.....

7. valves adjusted, balance shaft play adjusted...

8. New starting clutch installed.

9. Engine looked into here and there, pristine, shiny, with no signs of abuse or excessive wear...


This is how it works cold and this is the sound I get from the engine even when hot and the revs are a bit too low, basically, when riding in first gear slowly and pressing the brake while the bike merely coasts you can hear engine rattles like this and.. this is driving me crazy....

10. I used a stethoscope and the sound is everywhere, mostly I can hear it under the plastic cover that you see in the film - but there is nothing there underneath as far as I know - only the crankshaft end and the plane bearing.

Cold no choke used - intentionally, because once warm it idles faster and it is harder to hear the sound..


and a bit hotter, notice that it often misfires - wiring loom inspected, all connectors checked an resoldered - the condition of the wires inspected, 3 ignition modules tested, the coil pickup seems fine.

 

Video #1: sounds like a chain that isn't meshing properly with a gear. But you say all drive chains have been replaced. And the cam chain tensioner too. A fixed tensioner with no play.

There has to be a little give in the tensioner to allow for variation is chain length. And a too tight chain can cause mis-meshing problems. And if a new chain is used on a worn gear . . .

Try giving the cam chain just a little slack and see if that helps any.

Video two: When the engine is warm and rpms are up the noise is less. Both would tend to stretch the chain just a bit, perhaps allowing for more accurate chain / gear meshing. Or maybe it just raises the rattle frequency high enough that it doesn't sound as severe. Both of those are just shots in the dark. I really don't know.

Thought two: perhaps a glitch in the transmission allowing gears that aren't supposed to touch do so.

Did you find any metal in your oil when it was drained? Or in the oil pan?

 

I tried even with the new honda tensionser, and it changes nothing, so I suppose a proper slack is there.

As I said, in the hot video it just idles faster so I wanted you to hear the sound when engine revs a little bit higher, in the first video it is below 1000 rpm, and in the second slightly above. , if you drop the rpm down with the idle screw while the engine is hot, you get the sound from the first video..

The chain gears are ok everywhere....

Rather not, it would change on certain gears but it doesnt't, I can warm her up, shoot into any gear, apply the rear brake and once it revs down it will produce this chain sound...

All I found was a perfectly clean engine... I wish I had found anything...


Thank you...

 

Ok so you've eliminated chains, balance shaft, and many other factors.

Have you balanced the carbs - proper balancing with gauges?

Other thoughts - if it happens on the over run - gudgeon pins?

What fuel are you using? It almost sounded like a pinging - but not quite and at the wrong revs.

Ockam's razor - eliminate all other possibilities to be left with the cause.

Cheers, SB

 

two sets of carbs where balanced with the carb tune pro,

Fuel - good 95octane fuel the same as my other bikes use... nothing wrong with it.

Ockams stuff - yeah... I feel so stupid investing in her, you can do nothing about her being an old lump, I will be trying to cut the price and sell her...

 

An 'aha' moment occured a short time ago. Some time back, well actually fifty-six or so years ago, I was working on a 1954 Buick in Dad's shop after school. I removed, disassembled, cleaned and rebuilt its carburetor. Then dropped a nut into the intake manifold while putting it back on the manifold. Being young, inexperienced and, shall we say dumb, I decided to complete the job thinking that the nut would just lay down there. It didn't. It snuck by an intake valve into a cylinder where . . .

It sounded exactly like your CBR.

Have you had the head off?

Dad and I took the heads off that Buick twice and never found the nut. But both times it was hiding in there somewhere and made it's presence known when the engine was fired. About seven that evening Dad gave the customer a twenty and told him where a good restaurant was, said we'd have it fixed when he came back and sent him on his way. As soon as the customer was out of hearing range Dad fired the engine and revved the holy &%$* out of it. Suddenly the rattle stopped and all was right with the world. That lousy nut found an open exhaust valve and exited the engine.

Just wondering if a previous owner didn't drop something down an open plug hole, or maybe had the carbs off and dropped something.

You've eliminated about everything else. Might be worth a look.

I still wonder though. Where was that nut hiding? We really searched those cylinders.

Oh yeah. As I remember all Dad said was, "Don't drop nuts down the intake manifold next time. Okay?"

 

Might be worth to take a magnet pen and poke down from the spark plug holes just for the hell of it. Or if you can get your hands on an endoscopic camera, they're not that expensive these days specially if you got a computer at reach and can use one of those usb ones that don't have a dedicated display.

Just thinking... how high do the pistons come, is there even a theoretical chance that a nut might even fit in there... then again it could be a washer or some other piece of smaller crap.

 

no guys, that's not it....

 

OK, random thought time. The motor sounds like it is slightly retarded when idling - when you rev it it sounds fine, but idling to my ear, it is firing just before it should.

If it had a distributor, I'd be rotating it slightly (advancing). I'd be looking very closely at the ignition system and timing.

Cheers, SB

 

SB: don't you mean slightly advanced? Firing farther before TDC? Advanced timing would cause ping or knock. Whatever, I agree. Since every thing else has been eliminated ignition timing certainly bears looking into.