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

[mobile_bob]

Bob B:

in many ways this discussion in as much as i am taking part is in reality apples to oranges in many ways

my experience with resilient mounting of these engine's centers on the changfa 195 series, and the vast
majority of others are using 6/1 listeroids and a handful of listeroid twins.

out of curiosity, and wanting to learn from where i can (so you are the professor like it or not)
i have a few questions if i may

1. you mention your wineglass test, so out of curiosity i did the same with the cradle mounted changfa
to see what the outcome might be, i have no ripples and no distortion in the light reflected off the surface of the
water in my glass,, (sorry i don't drink wine, and all i had was an unopened bottle of white wine, and figured it is near clear
like water), so i think i am on par with your experience with your listeroid, but
my hat is off to you being able to tame a listeroid which is running at one third the speed, is likely far less refined and has
no counterbalance shafts like the changfa.

because of my cradle design the engine is able to flutter a bit at the air cleaner and the starter (opposing ends of the engine)
and i can locate the center of this movement on the timeing cover with a pencil, a place where there is very little almost inperceptable
movement up/down, side to side or precession (if there is any it is very difficult for me to determine or witness, much less measure it)
this centerpoint corresponds with the crankshaft centerline, so my crankshaft is not moving anywhere out of plane, although it is free to
do so on startup and spooling down when it passes through its critical speed. (i have lost my hand tach, so i can't tell you what that speed
is with any certainty, but would expect it to be somewhere around 500rpm)

so my questions

1. is there any harm in allowing the engine to run in this manner? if so why?

2. what possible unintended stresses might there be to the crankshaft?

3. from what i remember of your setup you have the resilient mounts under the subframe of your genset,
what if any movement does your crankshaft do when running at no load, partial load and full load?

4. have you witnessed any up/down, side to side or precession at the end of the crankshaft?

5. if you have movement does it seem excessive to you?

6. can you determine if there is any precession taking place?

i ask these questions because it is not everyday i have someone that is not only an engineer, but also someone that
has a resiliently mounted 6/1 listeroid.

i hope these questions are not trying your patience, i for one like to learn all i can, where i can, especially from someone
in the know such as you.

respectfully

bob g

[sailawayrb]

Hi Bob G.,

I am presently not feeling too well, maybe flu or something I ate.  Anyhow, I will review your questions more and get back to later this week with more detailed answers.  I do see movement in my crankshaft at start up and at shutdown (as the RPM passes thru different speed regimes and vibration resonant frequencies), but I do not detect any crankshaft movement during normal running.  I think Bill's paper circle test indicated that as well.  I suspect that flywheel gyroscopic force tends to stabilize the engine stand about the crankshaft once the flywheels exceed a certain RPM.  During operation, I notice maybe about 1/8" up/down movement at the top of the valve cover.  Anyhow, more from me in few days.   

Bsrgds,
Bob B.

[mobile_bob]

Bob B:

don't worry or hurry on my account,, i can wait

just get to feeling better ok?

besides it gives me some time to do some more research, dig out the old books, and make some measurements.
so maybe i can ask halfway intellegent questions.

thanks
bob g

[Veggiefuel]

This one's Smooooooth ! (not a twin)

Is that because of the double flywheels? Perhaps offset flywheel weights?

http://www.youtube.com/watch?v=3a6RZFHyIdQ&feature=related

Veggie

[piperpilot3tk]

This one's Smooooooth ! (not a twin)

Is that because of the double flywheels? Perhaps offset flywheel weights?

That one is smooth because the guy who assembled it was lucky!  This is good advertising for Anand but we all know very few ever turn out that smooth.  I am looking to pick up a few Anand engines soon, and if I get one that smooth i just may not be able to contain myself

[aqmxv]

PS - You may also want to study up on gyroscopic forces if you have not already done so.  When you try to move a flywheel from its spin axis, it resists (creates forces) that are perpendicular to the distrurbing force...not what most folks would initially expect.

http://science.howstuffworks.com/gyroscope1.htm

http://en.wikipedia.org/wiki/Gyroscope

http://en.wikipedia.org/wiki/Precession

Just to pitch in something from a slightly different angle of approach, one bunch of engineers who have to deal with precession and crankshafts a lot is aircraft propeller engineers.  Thrust and centripetal loads are common and comparatively obvious, but they also speak of 'p-factor' which is the force the propeller applies to its bearings when the aircraft pitches.

While the listeroid flywheel turns a lot slower, it's also very massive.  There's a lot of energy stored in that wheel, and I can certainly postulate excitement occurring if the mounting allowed change of axial direction for the flywheel/crankshaft combination.

Frankly, I think the Chinese single-flywheel engines are probably at a greater risk of this than an 'oid as long as the two sides of the twin listeroid are made as similar as possible.  A single listeroid is probably nearly immune.

[WGB]

I hope this hasn't been covered.
I work in a foundry from time to time, they have multi-million dollar, many ton, presses that jump inches with every stroke.
Foundations are deep in the ground, the press sets on a pad that is isolated from the foundation with a very expensive oil looks more like tar.
The pounding is unbelievable but they hold up very well.
My 6/1 Metro is still a work in progress. Mounted to 8" I-beams, it walked all over, I put 4 pieces of 3/4 heater hose under each corner between the I-beam and floor, stopped most all the problems, not much noticeable thump transfer. I don't think I would ever go the solid mount route.

[cujet]

I have a small success to report. I mounted Bruce's twin/ST/Frame assy on 4 elastomeric helicopter blade dampers. They seem to reduce the vibration by about half. There is no question it's a lister pounding the ground. However the vibes only travel 15 feet instead of into the house.

The engine is quite steady and has little motion. The mounts have visible motion, mostly a fore/aft shuffle. It seems to work quite well. Unlike mounting the frame on used aircraft tire tread, wich resulted in all sorts of shaking.

Chris

[pigseye]

Hi Cujet,
How does a civilian get elastomeric helicopter blade dampers? 

Thanks
Steve

[Horsepoor]

It's been awhile since I've posted a photo on this forum, lets see if I remember how. Here is a photo of the helicopter isolators "civilians" shouldnt have:

http://listerenginegallery.com/main.php?g2_view=core.DownloadItem&g2_itemId=2897&g2_serialNumber=2[/img]

[billswan]

here you go bruce



Billswan

[ronmar]

I am very happy with a combination of the two schools.  Generator frame attached to 1300# block of concrete setting on an inexpensive 1/2" thick rubber stall mat available from most any feed/farm store.  A body at rest tends to stay at rest, and it takes a fair ammount of energy to accelerate a 1300# block of concrete.  The rubber mat dampens out most all of the conducted energy.  Proven tech, easy to self fabricate and very inexpensive.  The stall mats cost about $35, and 1300# is about twenty two 60# bags(about $70 at my local box store?)   

I can just barely sense that the engine is running setting in my living room, but since I am still using the peppercan muffler, I am not sure how much of that perception is from the exhaust whump.  It surely isn't rattling windows or dishes.  Quite frankly, I find a little bit of feeling of the generator running re-assuring.  But I have also spent entirely too many nights sleeping on a ship at sea...