Vibration Control ...

[79XS11F]

I know that some people on the board have used a few different methods to control handle bar vibration including filling the handle bars with spray-able expanding foam.
I was wondering what you all think about this ...
Because my hop-up bikes engine will be mounted to the frame with solid alloy engine mounts, I was thinking that perhaps after the wielding is done, that I might drill some small holes in the frame tubes and fill the frame tubes with spray-able expanding foam. If the holes are placed in a fashion that they themselves would not weaken the frame would doing this reduce vibration? If it works on the handle bars do you think it would also work on the frame?

Rob

[tarzan]

I dont know about the vibration,but I run demolition derbys and I heard of guys putting that expanding foam inside their car frames to make them stronger.I havent tried it because it is grounds for disqualification.
Another thing is it would help keep water out of your frame if it had any holes or voids in welds.

[XSPastor]

The expandable foam might help a little. You really need weight at the bar ends. Some guys use buckshot or lead and use the expanding foam or caulk to hold things in place. Since it's usually a resonance issue, weight is the best way to do it. I will say that when I went to all the same value jets in my carbs instead of the stock staggered 110 and 120 set up, any vibration in the bars that I had went away. MUCH smoother at highway speeds. The first thing I would do if I had a vibration issue would be to check the motor mount rubber inserts and sync the carbs.

[79XS11F]

There are no motor mount rubbers to check. This engine will be mounted with solid alloy mounts. I don't know if vibration will even be an issue but I'm guessing there will be a lot more then there is with a stock set up.
Rob

[Pat Kelly]

Weighted bar ends should dampen handlebar vibrations, that's what they are designed to do. They are also easily removed in case they don't work.
If you look, there are already holes in the frame from when the frame was originally welded. The holes are to allow hot gasses inside the frame to escape during welding. I would tink filling the frame with expanding foam would add weight...... that's about it.
Just my opinion

[XSPastor]

Hmmmm...

Expanding foam doesn't hardly weigh anything. For that reason, it's not effective in dampening vibrations of the kind that come form this engine. I think you could fill the frame and not even notice a difference. It may thump instead of ping when you rap on it but that's about it. I'd be leary about filling the frame because it could cause it to not be able to get rid of moisture. You don't want water trapped in there.

[Korr]

Try a Bar Snake. They've been around for a long time check out the link

http://www.barsnake.com/order/secure.html

[79XS11F]

Well if it looks like there would be no benefit I will not do the spray foaming of the frame. I was thinking it might be helpful once the engine is hard mounted to the frame.
Rob

[trbig]

My question is.. WHY?

I can see mounting a motor solid if it was going to make 200-300 HP, but to do it for what you are going to see.. maybe a 10-15% increase? Remember that it's not just YOU that is going to be subjected to all that vibration. Electronic pieces, fuel in the bowls of the carbs, welds... Vibration kills batteries also. What is the solid mounting going to give you.. maybe 1 or 2 more HP on takeoff?

I know it's your bike and your choice.. I just wouldn't want numb hands and fingers for a couple more HP.

As far as the spray foam... No, it's not going to add any weight to speak of, but.. imagine a big bell or tuning fork ringing. You hit it, and the vibration keeps going. Imagine a big glob of spray foam on it. I bet it kills that vibration pretty quick. I'm not saying it will or won't work... but I can see some possibility that it could? That being said... you go spraying that stuff into things.. any thoughts of welding on anything encasing it in the future is out. I can imagine someone with your bike in the future making a post about something their idiot PO's did to their bike.. lol.


Tod

[81xsproject]

TR,
I believe it is to assist in stiffening up the frame for better handling.

[tarzan]

I wonder if you will really have much of a vibration problem at all.After all these bikes run pretty smooth.Unless your going with some ratical cams ,I bet it wont be bad at all.You could also use plastic like uhmw or even nylon.
You would get a little absorption but still be pretty rigid.

[trbig]

I believe it is to assist in stiffening up the frame for better handling.

The forks and brakes are the weak points for handling on these. (Besides the fact that they weigh what a heffer cow does..) Even with a fork brace, the forks will still bend in the twisties. Since the frame is being welded on anyway.. a couple stiffening brackets tacked on would help more than anything inside the frame would, but I've never heard of performance issues with these and weak/flexing frames. BUT.. his original question was about vibration.. .so that's what I was questioning.

It would take some $$$, but you could also send the crank off to get balanced and knife-edged. That automotive crank flinging around in there is the cause of most of the vibration.

[XSPastor]

imagine a big bell or tuning fork ringing

Exactly the point I was making in my post. Foam will help with extremely high frequency vibrations, but not even touch anything that comes from this engine. It's simple acoustic/physics. I can't think of any reason that you would want to rigidly mount this engine if you want a smooth, rideable road bike. If you're wanting to get rid of vibration, rigid mounting is going the wrong direction. I can't believe that filling the frame with flexible foam would have any stiffening effect either.

[Guy_b_g]

The reason you would want to put in solid motor mounts is to stiffen the frame (after all the engine is the stiffest piece on the whole bike), and if it's solidly tied to the frame, it can't help but tie everthing together and help prevent flexing (from what I understand the rear mount is the most critical since it's nearest the swingarm).

But there is a tradeoff just like almost everything else...and you know what it is, vibration.

If your focus is on handling and you plan to take every step you can to make the bike handle better, the solid mounts are one of the steps you take...

If your focus is on other isssues then it's probably best to leave the rubber mounts alone.

AlanB would be a good person to chime in here, his motor is solidly mounted, (I haven't heard any complaints from him about vibration).

[egsols]

Hey Rob,

You've probably read this, but just in case....http://www.xs1100.co.uk/solid.htm