How to reduce a twin's ground pounding, house shaking antics???

[cujet]

My twin is bluprinted and balanced, it's not a big time shaker. Yet it still pounds the ground like a pile driver (smells like one too!). I generally hae it close to the house and it is easy to tell it's running, as the entire house shakes with a very low frequency rumble. Remember, mine is on steel wheels, so it rests in the dirt, the grass or the gravel. But, it does not matter where I put it.

I was over at Bob's house and his twin is in a shed, mounted to concrete. It does exactly the same thing. Pounds the ground.

Thinking about Bob's single, he has it on tires filled with water. Besides the fact that it's well balanced, it seems to transmit much less to the ground.

Bruce has his twin mounted on large wood beams. My guess is that they also reduce the pounding slightly.

We tried a rubber tire section under each corner of a twin and it moved violently. That's not a good solution.

What do you guys think?

Chris

[sailawayrb]

To do what you want, you probably need to design and build a proper resilient mount engine stand.  I reckon a twin would be more challenging (i.e., more difficult to design and more expensive to build) than a single because of the twin's larger weight.  However, I believe this could certainly be accomplished successfully.

[compig]

Type of soil influences sound and vibration transmission. The principle for reducing or preventing transmission is decoupling. The time honoured method is rigidly attaching the engine to a large mass , surprisingly large as recommended by Lister. Others have used springs and rubber mounts.

[xyzer]

Chris,
I also have 2 6/1 portables that I beat my brains out on! From what I have learned when they are balanced the best you can get them by whatever means you use they are at a compromise between the reciprocating and the rotational balance. The 50% range works ok on aluminum piston light rod high RPM engines but I have found on a slow speed cast iron piston heavy rod engine it is another story! The reciprocating at 50%-60% wants to pound the ground and as you increase the % to correct it transfers the imbalance to fore and aft. After dynamically balancing one to a known % of 65% it had a slight pound to it but on a slick cement floor it would slowly walk. If it is pounding it is also lifting it allowing the fore and aft to affect it!  I increased the % to guessing 68-70% and the pound went away but transfers it to fore and aft but now it is not pounding and lifting so it can stay in place even with the fore and aft imbalance. Mine are resilient mounted and there is about .050" fore and aft movement with no ground effect. From my experience I would add equal weight to both flywheels and increase the %. If there is a rim on the flywheel I use modeling clay and do a seat of the pants adjustment. When you get rid of the pound and it stays put I take off the clay and replace it with the equal weight stick on wheel weights on the inside of the rim. At 50% the piston and rod assembly are only ½ corrected for balance the rest is what you are feeling.

[mobile_bob]

i have spent many hours argueing this issue, but nooooooo
we can't rubber mount an engine,, that is not in keeping with KISS

"the original listers didn't need no steeeeenking rubber, therefore neither does my listeroid in the year 2009"

ya,, bullshit...

sooner or later folks will learn that a ton of concrete is not the only answer to every question relating to listeroid mounting.


you might try the following

go down to the local truck stop and buy 4 rubber wheel chocks,

pickup your frame and place them under it, between the frame and the concrete floor/pad/block

unless your engine is a real jumper, it will sit there and run just fine
and you will have an idea what even a little rubber can do for you.

"you ever go rubber, you will never go back to concrete"

bob g

[NoSpark]

My single is mounted on a subframe made of channel with ½ rubber strips between it and the I-beams. The funny thing is that this fall you could feel it thump but this winter you can't feel it thump anywhere even beside it. I wonder if everythings just broke in or the frozen ground has something to do with it.

[xyzer]

Bob,
I found that even resiliently mounted they will transfer a thud to the ground....depends on the soil and conditions and your mounts. They do help for sure! IMO the problem lays in the fact at a 50% balance the piston weights 8.871lbs and the small end of the rod weights 2.259lbs for a total of 11.400lbs of reciprocating weight. At 50% there is 5.701lbs of non counter balanced weight going up and down. IMO that is the pound.....I believe even on a cement slab the pounding can be reduced by increasing the %. For resilient mounts I used 4 transmission mounts off a Volvo and they seem to handle it well.
Dave    

[SHIPCHIEF]

Ballance is a factor, as well as the load.  
I started with 1000 RPM and layers of rubber between the engine frame and the sub frame. It's 2 frame system is bolted to the cement slab in the garage. It shook bad, thumped the house and made the windows vibrate. I tried stick on wheel weights, and eventually cast a several pound piece of lead right on a flywheel, using clamps and plywood for a mould. I worried about that one; would the flywheel break from the added weight....or would the weight get loose and be flung thru the wall into the neighbors house? All that hand crank starting while trying different weight combinations lead to the electric starter mod.
I had to add steel to the sub frame to increase it's rigidity, still, the 3/8" steel bolts would break between the engine frame and sub frame. I removed the rubber.
I switched generator pulleys to reduce engine RPM. While lowering the governed speed from 1000 to the new speed of about 735 (or whatever) I noticed that about 940 was the sweet spot for my engine. Smooth as can be. Of course, no load was applied because I was reducing speed until my Kill-A-Watt said I was back to 60 Hz. The RPM I ended up with is actually pretty smooth, but the engine 'walks' from the rocking effect of the rotating mass exceeding the reciprocating mass, so it seems more side - to -side rocking than up- and - down rocking. Also the thumping increases with engine load and is most when the 8 groove serp belt is creaking at full load. At first I thought it might be a gen bearing, even tho I serviced them. But posts on this forum about belt slippage zeroed me in on the problem, although I don't have a cure yet.
When I run the house on this generator, the lights flicker and the house rumbles. Oh well.

[compig]

Do I correctly presume that genuine Listers don't have this problem ?

[piperpilot3tk]

Chris, speaking of balancing things, would you be interested in balancing the prop on my PA-28-180?  I flew the Cherokee up to Bowling Green yesterday to look at at BD4 with my hangar neighbor and we were talking about maybe dropping in one day and looking at your listeroid?  May be a good excuse for me to get the prop balanced and for you to make a little bit of play money.
What do you think?
Mike

[sailawayrb]

Bob G., I am beginning to understand your frustration with this whole subject...  If one isn't willing/capable to learn the mathematics and research/understand the subject, one is just relying on luck for resilient mount success and could well kill themselves in the process.  This subject has been adequately explained in previous threads for those folks capable and motivated to do it.  One also can't "balance" a Lister.  All one can do is shift the inbalance to another axis that one may or may not fully appreciate (i.e., shift mounting bolt compression/tension loads to shear loads).

There are some fundamentals that must be followed in resilient mount design...  The engine and generator must be mounted on primary structure that prevents any relative motion between engine/generator.  The resilient mounts one selects must be appropriate for the loads they will see and frequency that will be isolated.  To obtain in excess of 90% vibration isolation of Lister disturbing frequencies (approximately 11 Hz @ 650 RPM) will require resilient mounts that exhibit a relatively low spring rate (approximately 500 lbs/inch) that are not readily available/affordable.  Therefore, to achieve this level of "effective" low spring rate, it may be necessary to use resilient mounts of a higher spring rate (say 1000 lbs/inch) in your design but create this "effective" low spring rate via your design approach.  For example, two 1000 lbs/inch resilient mounts in series will effectively create a spring rate of 500 lbs/inch.  For my 6/1, there are 4 mounts between the primary structure and the secondary structure.  There are also 4 mounts between the secondary structure and the ground.  That's 8 total mounts for my 6/1.  For a twin, I could easily see using between 12 and 16 total mounts.

The reason original Lister's didn't use resilient mounts is because original Lister's predated resilient mount technology.  The other reason is concrete is simpler and cheaper than a resilient mount design and therefore more appropriate for vast majority of folks that use Lister's...then and now.

Bob B.

[mobile_bob]

Sailawayrob:

yes this is a very frustrating topic

a while back a friend and i were debating some topic, and out of frustration with me
he told me to quit theorizing and go build it!

so i did

my prime mover of choice as most everyone knows is the s195 changfa
it has twin counterbalance shafts and as such will run perfectly fine sitting on a pallet
not bolted to anything, but

once mounted to a frame and then sitting on the concrete floor, it does transmit the combustion event
all through the house, via the concrete slab.

this is not a rotary imbalance vibration but rather the combustion event itself being transmitted through the castiron/steel frame/concrete
then to everything from dishes in the cabinets, pictures on the wall, etc.

this was no surprise to me, i knew this is exactly what would happen and designed accordingly to start with.
i did the math, the geometry, and worked out the realitively simple vector physic's in order to design my resilient mounted system
the resilient mounts were not in play at first because i wanted to see what happens when the subframe is rigid to the floor.

once raise onto the mounts, everything changed
no more vibration to the floor, no rattling dishes, no pictures shaking and all that

the proof certainly is in the pudding so to speak.

in my opinion the key to success is careful design and as rigid a subframe as can be built, rigid does not necessarily mean
massive either, nor does it need to  be.
with a good understanding of proper subframe design, proper placement of the mounts, proper geometry, the need for very specialized
(derived from a bunch of math that a lot of folks couldn't be bothered with) is reduced.

i simple three point resilient mount with a forth adjustable spring mount to tune the system works incredibly well, one can get the design
approximately right, set the  engine at the design rpm, set the predominate load anticipated, and then dial in the 4th spring mount to get
damn near perfection in my opinion,, and the crankshaft centerline can be made to be the center of all movement so that it stays stationary in its plane, so that there is no gyroscopic stresses being imparted onto the crank as some folks are concerned with.

things like the specific angle that the mounts are installed at aid in control of movement, proper geometry uses the shear properties of the mounting system to aid in control of the fore/aft movement folks arrive at by balancing the engine's so that they try to scoot back and forth rather than jump up and down.

there is so much written on the subject and so many examples of how resilient mounting systems work, it just amazes me that folks are so slow to use the technology.

as for mounts you have provided excellent sources of info, and i thank you for that, i collect all i can on the subject.

one thing folks dont consider in my opinion as much as they should are the specialized mounts that are engineered and used
by the automakers, i know the response already "yes bob, but these are multicylinder engines"... but

some of these multicylinder engine's have had many thousands of hours and millions of dollars in development of mounting systems
that make engines appear very smooth to the driver,, some of those little 4 bangers idling with all the accessories on, while turning the powersteering against the lock,, jump and shake like hell under the hood,, but the driver is unaware of all this shaking up to and until the
mount finally fails at 200k miles.

some of these mounts provide isolation in all 6 degree's of motion (x, y and z axis and rotation around each) all for about 20 bucks or less
new and 5 bucks each used at the bone yard.

i used 3 such mounts on my system, along with the 4th adjustable (which is curently just a floor jack with a spring, and i don't use it all that
much in testing), they are readily available, cheap and easy to work with in my opinion.

i have little doubt that a listeroid single or twin of any size could be resiliently mounted and have an excellent result, i know you have had very good results with your setup as has a couple others that i know of.

sometimes i wish i had use for a listeroid, so i would have a reason to build up a resilient mount system for it
and do some testing, prove the concept sort of thing.

at least there are a few more coming over to this line of thinking as time goes along

bob g

[sailawayrb]

Thanks Bob G.  Hopefully not to digress too much from this thread, but I posted some additional comments and photos of my home automation system on the other computerized engine thread:

http://listerengine.com/smf/index.php?topic=2205.new#new

[xyzer]

Hmmmm......."twin counterbalance shafts" and "will run perfectly fine sitting on a pallet not bolted to anything" sounds like an easy fix to me ! ........shame on me!       

[rocketboy]

Get rid of that smelly piece of junk and get a Volkswagon diesel rabbit powered generator governed by a onan regulated VE pump.

All your problems will go away, tho.... you won't be able to fix it with a sledge hammer!

RB