Buzz Killl?

[Ben70_imp]

I'll keep you posted.

Ben

[dave]

Hello Ben, thanks for the great write-up. Your conclusion is that you have reduced the vibration significantly (I added "significantly", based on your comments). I am not doubting your results, but I would like to understand better exactly how such a minor change resulted in such a significant reduction in vibration. I studied dynamics of machinery, back during my college days, and I am not claiming to be an expert in this field (far from it), but if you could please provide an explanation (please don't hesitate to get technical because I think a lot of the guys who visit this site are really intelligent), I would really be interested to read it - and possibly learn something. Thank you.

[Ben70_imp]

Hi Dave! The physical difference in the intake cam is simply shorter duration on 1 and 2 cylinders by 10 degrees. Intake valves close 38 degrees after bottom dead center for 3-4, 28 after for 1-2. I really don't know why this produces a different tone or note to the exhaust, which with my Yosh exhaust was notable, and went away after I put the exhaust cam on the intake side. It still has a nice sound, but it sounds to me more relaxed and comfortable with what it's doing, rather than urgent and forced, or fierce.
The sound was possibly what they were going for, but what also went away was the harmonic buzz. Different than a vibration, which I believe is what you get with an inline 4.
Many either don't feel it or are not bothered by it. When my wife asked me why I was taking apart a perfectly good motorcycle and I explained it, she said " Your hands go to sleep when you watch NCIS". Hah.
But if you have the bike on it's sidestand and increase rpms steadily you may note that as you pass through 2800-3300 rpm it changes from vibration to vibration and buzz, which bothered me after a relatively short ride. Often used my throttle lock/ cruise control to free up my hand long enough to get the feeling back.
I also found that I was not as aware of the rpms. I found myself forgetting to shift into 5th.
So I can't really explain in technical terms but apparently there is a frequency that causes it. I was worried that I would get a "normal" cam on the intake side and it would still have it, but it does not. Vibration, yes. Harmonic buzz, no.
I found a cam guy that isn't sure if I knew what I was talking about because I think he just couldn't process the concept of altering a cam like that for purposes other than performance. He agreed to have a look at it and whenever that shakes out I will give him credit if everything works out.

Ben

[Cormanus]

It's taken me a while to find this again, but the quote from the Honda Designers Talk propaganda back in the day was:

Quote:Sekiya:
On the hardware side, phased valve timing gives the engine its characteristic feel around the 3,000 rpm range. How did you create the engine's personality?

Minami:
Basically, straight-four engines run smooth as long as all four pistons move the same way. My initial thoughts were, to give the engine a deep rumble, we'd have to change the movement a bit.
We ended up shifting the valve timing of cylinders 1 and 2, compared to cylinders 3 and 4, and by continuing to change the gap, found the right combustion out-of-sync feel.

Sekiya:
Valve timing is usually changed or made variable to increase output, but your aim was completely different. Maybe the exact opposite of conventional wisdom.

Minami:
Precisely. We took the opposite approach to conventional thinking, so we weren't sure if it would work.

[Ben70_imp]

Thank you, sir! The prowl through the Basement of CB1100 Lore paid off. I will happily refund you for lamp oil.
Does Dactyl Petroleum handle that product?

Ben

[Cormanus]

[dave]

Hi Ben, thank you for your reply. It's pretty easy to understand why the sound would be different. I am sure it's a very complicated mix of vibrations within the engine, coming from various sources, that result in the vibration you feel at the handlebars. Somehow the different geometry of the replaced camshaft affected how all these forces work together, and the result is you feel less vibration. I was hoping for a good technical explanation, but I understand if you don't have one. There's a lot of really sharp people who visit this forum, and maybe one of them will take the time to post a good explanation. I would really like to know how our bikes would run (increased hp, less vibration?) if the cam lobes were the same for all cylinders. Good luck with your experimentation, and please keep us informed of your results.

[Cormanus]

In the engineers’ talk quoted above it’s hard to know whether the ‘rumble’ Minami is talking about is aural or tactile. I assumed the former, but who’d know.

[Ben70_imp]

I think they were going for aural and got tactile thrown in. It was never gonna be a Curtiss-Wright.

Ben

[Ben70_imp]

Just addressing the topic of exhaust noise, when I got my CB the original owner had installed the full Yosh exhaust system. The salesman revved it in the parking lot and it popped, which he apparently thought was a cool selling point.
I told him I'd buy it if the stock exhaust came with it. Next day the stock exhaust had magically been unearthed, I bought the bike and the stock exhaust is still hanging in my shed. I disabled the PAIR and the popping on decel diminished drastically but it still did it on downhill deceleration.
As the popping is caused by unburnt fuel igniting in the exhaust, it is not a surprise that premium fuel, which burns at a slower rate, makes it worse. Or better if you like popping. It is also an indication that this engine was designed to run on regular fuel as recommended.
An interesting thing about the modification of installing the exhaust cam on the intake side is the noise on downhill decel changed to a muted burble. So the fuel mix is being burned more efficiently. I suspect it is because it doesn't get as much fuel to begin with, because of the difference in cam profile, as also indicated by the reduction in hp on the dyno.
SO, the snarl went away and the popping went away, the things that were supposed to be desirable traits by the design team and the used bike salesman. I suspect some of both may come back when I get my finished product in place. I am waiting for the cam man to receive my cam so I can find out what he thinks. Also waiting to hear from Guhl on my computer. So I have bike parts spread all over the country in the midst of a global shutdown. Fingers crossed.
As a side note on exhaust noise, Google Mini Cooper exhaust burble, the forums are funny as heck (to me).

Ben