thnilsen

Have anyone used the Graupner Vibration Absorbers (product number 6853.?) for mounting engines mounts to the firewall?

I haven't found out what the thickness of the firewall needs to be when using these. Are they supposed to extend beyond the firewall so that the rubber bits sticks out on the inside, or is the firewall supposed to cover them fully? Anyone got any experiences with these?

Any suggestions appreciated.

Regards,
Thomas

Jetdesign

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Can you post a link?

thnilsen

The product can be found on the Graupner site as http://shop.graupner.de/webuerp/servlet/AI?ARTN=6853.5

Regards,
Thomas

Villa

Hello vangeliz
It is important that you obtain installation instructions from the manufacturer for the exact mount you will be using. The thickness of the firewall is critical. You may have to make it thicker at the mounting points. Generally, the flange end is on the engine side of the firewall. The hole is sized so the mount round section fits just a little tight. The mount probably has a female thread inside. On the other side of the fire wall would go a proper size flat washer and a nut. When the assembly it properly tighten, a flange will form on the inside wall of the firewall, perhaps a little smaller in diameter than the current existing flange. In a proper installation, there will be the right thickness of rubber at every point between the engine mount and the firewall and ALL of the rubber will be properly supported. I believe that the holes must be chamfered (round the sharp corners) on both sides of the firewall. As you can see, there are a number of variables that must be correct.

thnilsen

Thanks for the info Villa. the biggest problem is that Graupner does not provide any details on the firewall thickness for using these mounts.

I've mounted it more or less like you describe now, using a washer and nylock nut on the inside. However, I'm not sure about how much of the rubber is supposed to be the inside to make the seal. That's why I was hoping someone here would have a better idea of the correct firewall thickness.

Regards,
Thomas

Villa

That it terrible that the German manufacturer does not provide dimensions. I looked at their website and I noted that some dimensions were provided, but it seems to be only for one size. I do not read German. If I were you I would contact the manufacturer and insist that they provide you with the requirted dimensions. If you get nothing else, this is what I would do: Measure the total length of the threaded insert inside the rubber device. Subtract the thickness of the flange. Then subtract the thickness of the rubber wall at the other end of the isolator. Use the resulting dimension as the minimum thickness of the firewall at the point that the vibration damper is located. I must caution you that it has been many years since I used these types of vibration isolators (like 30 years ago) so I may be wrong. Plus I am guessing at the above dimensions. Without the proper dimensions the vibrations isolators will not be able to perform correctly and in the worst case the engine may even fall off. It is even possible that the correct method of locating the vibration isolator in this application is opposite to what I have described. Get the installation instructions!!!!!!!!!!!!!! As a last resort, you might look up an American equivalent manufacturer named Lord(possibly Lord Manufacturing). They made the rubber vibration isolators that I have experience with. They may have an on-line manual that you could look at and make comparisons. I used isolators just like the ones you are using, but manufactured by Lord for mounting an 60 size R/C engine. I also used them at my work to mount large Diesel engines, electric motors, and air compressors. Graupner may just be a model airplane parts supplier and may not be aware that the mounting details are very critical. Possibly if you contact Graupner they will give you the vibration dampner manufacturer and you can contact them. I'm sure that most people will believe that I am making a mountain out of a mole hill (that what I have been stating has no importance). That has no meaning to me. I am a retired Mechanical Engineer and know that some things are critical. Let me know when you get more information.

Deadeye

Here's the translated page: http://translate.google.com/translat....5&sl=de&tl=en

Villa

Hi Deadeye
Please do not take this as a criticism. Thanks for your help. I have been interested in computer translation for many years, primarily because I speak a second language and know a little about a third one. I have yet to see a free one worth anything. I do not know if there are better ones available. Read what the computer translated. Much of it cannot be understood.

Deadeye

Villa,
While I realize that computer translators aren't the best, it still gives the gist of the product (not to mention some funny phrases!). My wife managed to teach herself to read and write Arabic starting with computer translators. They are mearly a free stepping stone to learning another language. Ajeeb by Sakhr software was probably the most helpful for her...but it is geared towards Arabic. Rosetta Stone sure is advertised alot, but she never liked it.

Anyhow, getting back on track, I am interested in this Graupner product, as I like to soft mount all my four strokers. I wonder if there is a US alternative?

Villa

Hi Deadeye
The American manufacturer, Lord Manufacturing has changed their name or maybe I have forgotten. I just Googled it and their site is http://www.lord.com/Home/ProductsSer...0/Default.aspx
You can see the same engine mounts as is the subject above. I quickly looked for a catalog but did not find one. I did not spend enough time on it. When I was working in engineering design I used their catalogs so there must be a way of getting one or seeing one on the Internet. I noticed that Lord is also in Germany, so the pictured vibration isolators, above, could be Lord, but probably metric. The catalog is needed to get the correct mounting hole dimensions so the vibration isolator will give the right performance. I retired before all of this information became available on the Internet, so I'm just guessing that the info is available in that manner. I like to keep my hand in engineering. You will have to identify the actual isolator you are using buy catalog number since they will all look the same but will change by rubber compound and hardness, etc. Then you can study the catalog. I hope that this post helps the original poster also. Let me know what you find.

thnilsen

The google translation does give room for interpretations :-) But I guess that the "DB" measurement of 10.2 -10.5 might be the firewall thickness it is supported on. Not sure what the "s" entry is supposed to be good for?

Anyway, I fired of an email to Graupner to see what info they can provide on this subject.

Regards,
Thomas