High pitched whistle or whirl from engine

[Snakeoil]

Hi,

I'm a newb with a newly acquired '67 CL77. Bike runs really strong. The only think I noticed that I need to investigate is a very high pitched whistle or whirl noise from the left side of the engine. When I'm riding the noise seems to vary with throttle position, which makes me think it is a whistle from the intake/carbs/filters. But it sounds more mechanical to me. At standstill, with the bike on the stand, it sounds like it is coming from the left cam cover area. It is very hard to determine or describe. At some points it almost sounds like valve lash clatter.

Any suggestions, ideas before I tear into this. Carb are easy and will probably dig into them tomorrow. Bike is extremely cold blooded. Somebody gutted the stock muffler so probably running a bit lean, although plugs look fine. Want to go thru the full tune up exercise just to make sure all is correct.
Thanks,
Rob

[bonjour]

Does the sound get louder, or does the sound 'rev up' with the engine ?

My CB50 makes a sound like that when the cam chain is to tight, maybe you find a clue there..

[Snakeoil]

No, it's not tied hard to RPM. So everyone knows, I've got plent of engine experience and work for a living with Gas Turbines. So troubleshooting and problem solving has been part of my life for a long time. This is related to RPM, but not 100% as say a bad gear or bearing might be in that as speed goes up or down the sound tends to track it. It's seems more tied to load in that throttle changes can find both noisey spots and quiet spots while traveling down the road and modulating the throttle a little up or down.

With the bike on the stand, I can hear it, just not as loud. I spend the day meticulously cleaning the carbs. Carbs are in excellent condition and properly tuned now. They were pretty close now that I've had them apart. So my point is it is not a carb or intake whistle. All o-rings were replaced and everything is sealed up properly.

Noise is definitely from the left side, top end. Not much noise at idle, but when you rev it, sound very metallic and like valve clatter. No noise at all on the right side. I'm thinking I've got very loose valves on the left side.

It could very well be that this is a normal noise for these engines. I'm not around anyone who has 305 engine experience. So I cannot ask if this noise is normal. All I know is with the bike at speed, that noise is almost piercing in nature.

Thanks,

Rob

[Snakeoil]

Dug into the valves this morning to eliminate or confirm the noise is valve clatter. What I found was Exhausts damn close to spec, but Intakes were way too tight. Intakes were actually too tight to back off the lash adjuster by hand with the jamb nut loose. At least when the bike was cold, it was preventing the intakes from seating.

Set both Intakes and Exhausts to 0.004". Fired up the bike and there was a significant different.

First, I noticed a startling rise in compression. Bike fired on first kick and actually kicked back enough to hurt a bit. Fired and ran on the second kick and settled down to a nice loping idle after I revved it. No longer is this a cold blooded beast. Obviously, low compression was making it need to fully warm up. Could be there was enough thermal growth to let the Intakes seat, because it would idle when warm. But it would never want to leave the line in first. Tooks lots of revving and slipping the clutch to get it to go. That problem is gone, too. Bike has a lot more snot right off the line.

High pitched noise is still there. I think it is a left side cam bearing. Cannot imagine the chain making more noise on one side or the other. Valve clatter is definitely ruled out. Going to pull the cam cover off the left side of the spare engine to see what I can see. Then might pull it off the running engine. Screws there, as well as all the head fasterers have never been touched before. Flats are all perfect.

Engine has 14K on the odometer, and I suspect it is correct because the bike appears unmolested other than some cosmetic sprucing up by the guy I got it from.

regards,

Rob

[Snakeoil]

Last night I took the bike out again, specifically to try and figure out what is in play here. This week I went to look at another CL that was for sale and was a running bike. Valve clatter on the left side is the same as mine. But no chirping noise like mine has. So the run last night was to try and narrow down the variables effecting the sound

First, reving the bike or holding the rpm up with the bike on the stand does not produce the noise. Bike has to be moving down the road. The other factor is the throttle must be between closed and opening. By that I mean the spot at which the bike is not decelerating or accelerating. It's when the engine is under partial load.

I cannot imagine the load on the cam bearings or valve train to change with throttle position. The noise is there regardless of bike speed, gear selected or engine RPM. I can get it do it at 60mph or 30 mph. It's a matter of modulating the throttle.

Chirp seems to be the best word to describe it. It is very similar in pitch to the valve clatter you hear on the left side of the head. But when present, is significantly louder. Everything is telling me it is intake/carb/air filter related. But I'm wondering if there is another feature of the engine that could change with throttle position. Crankcase pressures should vary with RPM and be determined by the size of the breather system. But I'm not sure if between between acceleration and deceleration will make for the correct conditions for the breather to whistle.

The chirp is loud enough to sound like an actual squeal, like a dry bearing. But a dry bearing should squeal all the time and get worse with RPM. It should at least be there all the time in varying degrees.

Any experienced 305 engine builders here every experience anything like this? I'm really stumped. I don't want to tear into the top end for nothing. I'm going to try and run without air filters this weekend to see if it makes a difference. I know the filters are new aftermarket filters. Rubber intake snorkles appear to be original as they are hard as a rock. I might have a leak at one of the hose neck connections. I had them off once when I disassembled and cleaned the carbs. But never ran the bike without them. I cannot remember if the sound was there before I did the carbs. You know how it is with a new bike. All the sounds run together at first. I noticed this when I took a long ride to a shop to get it inspected.

One last piece of input. If I close my knees and hold them tight to the tank, the sound is greatly diminished. Open them up and it returns. I tried using my left hand to shield different areas to affect the sound but had no luck. Only holding my knees tight to the tank had a noticeable effect.

Any insight would be appreciated, guys. It's driving me crazy.
regards,
Rob

[Hotshoe]

Possible exhaust leak? There's a crush packing inside the head that seals the exh pipe flange to the land in the exhuast port that could be leaking. Check the head around the exh ports and the exh pipe flanges for sooty telltales and the 10mm nuts that secure the exh pipe flanges. The last notation about knees and gas tank might point you toward a harmonic vibration noise.

[Snakeoil]

Thanks Hotshoe. I had the exhausts off the bike and don't think that's it. I do have another set of pipes I can try if I cannot figure this out.

If it was a harmonic, I would expect it to be speed or RPM sensitive, but it isn't. And I'm not gripping the tank with my knees, just moving them so they are more between my ears and the engine. I tend to think my knees are deflecting or perhaps muffling the noise.

But your comment about exhaust gaskets and knee position makes me wonder if there is not a pinhole in the exhaust pipes somewhere that chirps at just the right flow conditions, which would be related to throttle position. Remember how VW Beetle exhausts all chirped from the holes in the twin silencer pipes that came out of the muffler? Hmmmm, need to think about this and take a close look at everything.

I will double check my exhaust port to make sure it's not a leak.
regards,
Rob