Squeak from exhaust system rubber hanger

[fscliment]

Hi Experts,

Now we are dealing with this issue: High frequency noise from the vehicle exhaust rear hanger due to the engine movement.
The root caise is the friction between rubber of the hanger and the steel of the rod. A stick & slip phenomenon happens providing the noise.
We are now testing a lubricated rubber proposed by a supplier and it works. But this rubber has also different geometry.

Do you have some experience in this cases?
Would you propose some technical meterial regarding lubrified rubbers?

 

[kchan711]

Hello fscliment,

I am a Mechanical Engineer and have spent a great deal of time building and racing motorcycles (Buell bikes for clarity). This problem is frequently encountered because of the vibrational issues with a typical V-Twin motor. The Buell chassis also has the engine mounted on rubber dampers to isolate it from the frame; hence, the bike gets the "shakes" at low rpm.

Converting the exhaust to a low-restriction race pipe further translates vibration into the exhaust, a serious mounting and noise issue. A few concerns needed to be addressed for proper mounting of the exhaust:

- Motorcycle exhaust is short; therefore, it is hotter in comparison to many other exhaust lengths because of inadequate heat loss through the headers and pipe.
- Rubber mounting the exhaust would solve the noise issue, but heat capable rubbers provide less dampening (heat resistance vs. elasticity, they are generally inversly proportional).
- Wear issues and mounting configurations need to be considered, we don't want things coming apart at high speeds!

The solutions I used are as follows:
- Closer to the manifold, I used a high-temp silicone rubber sheet (encased by a stainless steel sleeve) directly connected using a steel triangle to the engine crankcase.
- Towards the rear, I have an expanded stainless exhaust with adequate heat dissipation, which allows for a significant drop in temp (you can touch it with your hand). This is directly attached to a steel arm, which is embedded within a rubber mounter.

In your case, I would not recommend allowing an exhaust to wear on a rubber sleeve. This will eventually fail due to deterioration of the rubber (constant heating and cooling combined with frictional motion even with the lubrication). What I would recommend is attaching a weldment (plate most likely) directly to the exhaust tube, which would then be bolted to the vehicle frame in between two rubber dampers of your choice. This prevents the "slide and stick" motion you encounter, allows for the exhaust motion within the rubber dampers deforming under load and also provides for adequate sound dampening through the vehicle frame. This solution, however, will find other vibration issues within the vehicle frame near the mounting point if they are not properly secured.

Hope this helps. If you need a more detailed or clearer idea, let me know.

 

[fscliment]

Kchan: Thank you very much for the info, that's a smart explanation!!

According to your comments, you disappoint with this kind of attachments basically due to the rubber deterioration after heating cycles.

It is very interesting for me the solution that you propose instead rubber sleeve. I think I can have an image but could you please send some scheme / reference describing this solution?
I hope I'm not asking too much.

Thank you very much again!!!!

Regards,

Francisco

 

[kchan711]

Hi Franciso,

Give me later to this evening to provide some diagrams and pictures of my solution. Expect a posting within about 12 hours. Talk to you soon.

Regards,
Kyle

Kyle Chandler

http://www.KylesGuide.com

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[kchan711]

Hi Francisco,

I went ahead and modeled a quick concept of my idea based on the photo you supplied and provided a PDF link for you to download. The model uses the same support that I believe is in your photo, which looks like it is welded directly to the muffler.

The design uses a simple welded triangular member being mounted to the vehicle's support bracket (in your photo) using hex bolts and neoprene rubber dampers. I used off-the-shelf dampers from McMaster-Carr, product # 6309K2. This will prevent unwanted vibrations and noise while keeping the exhaust steady. The dampers themselves allow for a minimal amount of deformation to account for the engine movement. I propose the total project cost at being around $15-$20 (reusing some parts) excluding labor.

Hope this is sufficient. If you need further design help, feel free to get a hold of me on this thread or use my contact page (click OTHER) on Kylesguide.com .

Regards,

Kyle

Kyle Chandler

http://www.KylesGuide.com

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[GregLocock]

Bear in mind that the exhaust expands by ~ 10 mm when it warms up, and the engine moves in various ways in use.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[fscliment]

Thanks Kyle!!

I appreciate a lot your effort. I work as NVH engineer for diesel powertrain in Spain. If I can help you at any time please ask!!!
I also saw your webpage, very intersting!.

Best regards,

Francisco.

 

[kchan711]

To tell you the truth, I could use an extra pair of eyes looking at the website. Not much, just give it a look and offer suggestions. We just started developing it as a quick stop for engineers. If you could mention anything that you might want to see or need being an engineer(spreadsheet software, calculators, links or general info), it would be greatly appreciated.

FYI, I work as a Research Engineer for two companies in the States, a defense firm and a nanotechnology company (very different roles). I also once owned a Hi-Fi Loudspeaker company for about 7 years. Vibrations and correct music reproduction were a huge concern in the final product. It's an extremely interesting problem area. If you ever need any other help, let me know.

Regards,

Kyle

Kyle Chandler

http://www.KylesGuide.com

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[Rob45]

When you mention that you have a "high-frequency noise" due to engine movement, this makes me wonder if there is a problem with a lack of rigidity in either the rod or the rubber isolator housing.
(Both look rather flimsy in your photo)
This could be indicated if the squeaking noise only occurs at certain engine operating speeds, for example.

If this is the case, I would suggest doing some point mobility testing of both the rod and the isolator housing and mounting pad, and see if any of these results show resonances at the noise frequencies.