Genset isolation bushings

[Paladin]

I know this has come up before but I can't find what I'm looking for anymore in the archives.

What have people used for vibration dampening bushings for their genset? I've looked around a bit for gel but most are very expensive and I don't know how useful they are to begin with. I want to mount my Onan 6500 in the condenser compartment and I'd like to dampen any vibration and then also work on noise although it's not that loud to begin with.


-Dave

[luvrbus]

Small air bags are your best they can be found used at truck wrecking yard on the seats or Dick Wright sells the bags new for generators  




good luck

[Lin]

I used some chunks of rubber.  It was  big improvement over having nothing.  My generator, however, is gas.

[Hartley]

Tractor supply sells rubber mats made for horse trailers and stalls,

Find the 5/8 to 3/4 inch thickness and cut damper pads from that, also
it absorbs lots of noise and vibration. I used pads I made to place my
Onan 10kw Diesel on and placed large washers with 5/8 bolts to anchor
the genset.

It flops around when starting and passes no vibration to the chassis that I can
tell. ( accidentally did hard mount part of my exhaust and get some noise from that
but it is just enough that I know the genset is still running. ( used a kabota tractor muffler!) Sweet and noiseless. Just makes a whooshing sound if you listen for it.

That way I saved the $300 that I would have spent on the mini-airbags too!

[John316]

I like Clifford's idea. That is probably what we would do if we were going to do it again. We hard mounted ours right to the floor, and the vibration really hasn't bothered us at all.

Then again, I am not going to take ours out, and reinstall it. Ours weighs right around 1k lbs empty. It was hard enough getting it in there on a flat surface. However, getting it up on airbags would be a chore. We have a 20kw diesel.

God bless,

John

[centrix29]

I read once about someone that mounted his genset on tires 4 tires.  I bought 8 inch tires to do it but have yet to install them.  Another project on the back burner but a good idea I think.

Good luck with your projet!

Pat

[luvrbus]

Trucks have the mini bags on the cab and some seats I buy them at a wrecking yard for 10  bucks each and if the generator is to high just recess the bags in pipe to any height you need.  
Like DR Dave no way would I pay 300 bucks for set  



good luck

[JohnEd]

I am sure that small air bags would be useful.  Rubber mat would also have some merit.

Search for "shock mounts".  I look after I post this.  They come in a variety of sizes and materials.

If you just want high freq vibs from a heavy item tamped down then air bags are good.  Unfortunately, in my case anyway, my gen has high freq vibs when running under constant load, has more robust vibs when loaded suddenly, as in an AC kicks in a compressor, and huge vibes when the thing starts or stops.  Mostly it just sits in there and hums along but then it will shake violently and really get some moves on periodically.  The thing about those air bags is that they don't "capture" the gen really well.  They provide little resistance to movement.

Rubber has the characteristic of allowing itself to be stretched slowly with little resistance.  Try to move it quickly and the resistance goes up.  Either on compression or expansion.  That is why it is such a great performer as a sound or vib isolator.  

There is also "liquid filled" rubber isolators.  They are stellar performers also.  You can shove the equip and it moves easily.  Sharp blows to the floor are not transmitted to the unit and if the movement is dramatic and low freq, such as a bus would encounter with a rough road or bump, the unit will move freely and not snap the mounting hardware or foundation.

Simple springs or coils of common cable perform well and also provide for the effective capture of very heavy machinery/weights in marine environments where ships roll or take sever impacts from waves or gun mount shock.

Point being that there is a lot of proved tech out there and most of it is very expensive.  Get your mounts, liquid filled rubber is my recommendation, from surplus or used sources.  Be certain that you are sizing them for your load/weight cause if you get them too stout they will "transmit" the vibrations just like you hard mounted them.  Rubber is the best IMHO.  I have no tech or engineering quals on this subject but I did install and maintain shock mounted equip in the mil and civ ser for 30 years.  No credential in that whatsoever.

Mil surplus and eBay are your best bet but make sure the mount is rated for your weight application.  Anything is better than nothing....even rubber mats and they are not bad at all.

John

[JohnEd]

I think that the ones that Cliff is recommending function like the liquid filled rubber I was recommending.  If you can get ones rated for your load then I think that is a superb solution.  Might be able to do better from a function standpoint but not enuf to encurr any great expense.

I might add:  the mounts for a seat will not be adequate for a 3 to 400 pound gen but if you double up on the mounts, that would be superb and really cheap at $10 each.  Good info Clifford.

Thanks,

John

[Paladin]

Very good answers and ideas, much to mull over. Now time for some research and decisions.

Thanks everyone!

-Dave

[Ednj]

Did you look at these = http://www.mcmaster.com/#rubber-isolators/=3ofsgf .
or grainger isolators.

[Hartley]

My answer is also qualified by one other thought which I went through many iterations
before I figured it out.

The stacked rubber squares of about 3 inches across and that each square is only
3/4 inch tall, In order to allow for overhead clearance and movement inside the
compartment I used 3 squares stacked on top of each other.

My Onan does not have the square metal sound box around it so it floats in the compartment with enough clearance on all sides to reach around the ends and top
to reach things like belts, pulleys and the electrical control box without needing
to remove the whole mess to change a belt or tighten the alternator due to belt
stretch.

Of course my Install is gastly and nasty looking and the radiator was moved away
from using the stock fan by about a foot rearward. It is hung on an aluminum box
with a deflector that sends the air out and down through the original condenser fan
hole with an electric temp controlled fan. The fan pulls all air through and across the
generator and engine before dumping it downward and towards the back.

I placed an aluminum sheet over the mesh and mounted 1/4Inch leaded vinyl to it.
Then cut out a couple of air inlets at the lower forward end to have all the air go into
and across the generator head air intakes and then across the engine.

During the 2 1/2 months that the generator ran continously I almost forgot it was there.
I never had any overheats or other problems that weren't self inflicted such as not tightening the alternator/water pump belt, But that took 10 minutes to change.

The fan is set to come on at 175 degrees and does cycle under normal loads.
The engine is set to shutdown at 210 degrees with a thermal cutoff sensor.

My generator has the 4-cylinder kubota engine, The newer ones have a 3-cylinder
engine that vibrates more for some odd reason. They take a little better isolation to
get the vibes out. My rubber mat stuff works great on them too.

Like I implied, I am cheap and a hack at getting things to fit and work. But when a plan
works I kinda stick with it and see how it works.

[TomC]

I would highly recommend calling Dick Wright at Wrico International since he has experimented with generators for years.  It will save you alot of expense trying to end up with the correct isolator.  Good Luck, TomC

[NewbeeMC9]

I had an old ford ranger with the 2.3  that had the liquid filled rubber for motor mounts.  I believe they were pretty cheap at the OtterZone place when I had to change one.


http://www.autozone.com/autozone/catalog/parts/partsShelf.jsp?categoryDisplayName=Collision,+Body+Parts+%26+Hardware&fromType=parts&fromString=search&parentId=43-0&currentPage=1&filterByKeyWord=motor+mounts&isSearchByPartNumber=false&navValue=14300154&categoryNValue=14399999&fromWhere=&itemId=154-0&displayName=Motor+Mount&searchText=motor+mounts


But check page 1362 on Ednj's post,  cheep, cheep!!!!   You gotta love McMaster Carr

[kyle4501]

I like the pneumatic tire idea - you can mount channels to the floor use a couple more to make ramps to roll it out of the bay for service or repair.

A U-bolt or strap over the tires will secure it in place. Changing the air pressure in the tires will change the dampening, so you can 'tune' the system if needed.

Lots of choices. . . .

The isolation bushings need to be sized properly so they can absorb the movement effectively.

A good read to help understand a little better:

http://www.fabreeka.com/tech/Primer_Vibr_Isol.pdf


A thread that also discussed this (I remembered it, but it still took a while to find!)
http://www.busconversions.com/bbs/index.php?topic=1856.0