Author Topic: engine mounting v 4.0  (Read 77313 times)

mobile_bob

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engine mounting v 4.0
« on: December 16, 2006, 02:02:32 AM »
this post is for the purest in the group, those that want more info on concrete mounting of the engine

http://www.slideruleera.net/FoundationsForCompressors.pdf

http://www.slideruleera.net/MachineryFoundations.pdf

the first link is particularly interesting when considering concrete as the mount of choice for a compressor or an engine
seems somewhat opposed to that of the lister recommendation, which is not to say lister had it wrong, but

it would appear there is a case to be made for a shallower, but larger in length and width concrete block.
which opens the possibilty of a shallow, relatively large base that would work well with a genset i would think.
coupled with the matting that they refer to, might be the best of both worlds, low vibration, rigidity, safety, and low sound/vibration transmission
isn't that what most folks want?

not trying to stir the hornets nest, but passing along info for those that are so inclined to read it.


bob g
otherpower.com, microcogen.info, practicalmachinist.com
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Doug

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Re: engine mounting v 4.0
« Reply #1 on: December 20, 2006, 01:44:19 AM »
I got the same ideas from the information you posted Bob....

I now have a Ukranian mechanical engineer, an Italian black smith and several millwrights at work discussing the best way to mount a stationary engineer on a block.

The engineer is clever...
The millwrights are practical...
The black smith has done this work in the old country...

I think its a case of ballance for best performance first and mount on the biggest practical block. A practical block seems to be open to debate...

Doug

mobile_bob

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Re: engine mounting v 4.0
« Reply #2 on: December 20, 2006, 04:20:41 AM »
Doug:

what i have been wondering in consideration of the concrete block and issues with isolation from the house slab and the underlieing soil is

what if one was to poor the floor, leave an opening for the engine base, form up the sides of the opening in the floor at an angle of perhaps 60 degrees
then line the sides of the opening with some high density rubber and then poor the engine base within the rubber lined opening

one would then have an isolated concrete base that would only tighten if the soil compressed or shrank away, also the engine concrete base would be tightly contained
and not be subject to soil shrinkage from the sides which allows fore and aft movement, rocking would also be abated.

i am sure there are other considerations such as the engine concrete base would exert large forces on the floor, so additional rebar would have to be incorporated to keep from stressing the floor and cracking,,

but it should be possible to do

i think you then would have a very well contained, isolated, rigid and solid mounting system.

just thinking

bob g
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biobill

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Re: engine mounting v 4.0
« Reply #3 on: December 21, 2006, 03:34:42 AM »
Bob,
  I tossed that one around before I went the way I did. Unfortunately, the proper material for under your floor (something that drains well like crushed stone) would be all wrong as far as vertical stability goes. You can compact it but it's not going to stay put at 60 degrees. I suppose you could pour the walls or maybe find a precast cistern  of appropriate dimension and set that in place before you pour the floor.
                                               Bill
Off grid since 1990
6/1 Metro DI living in basement, cogen
6/1 Metro IDI running barn & biodiesel processer
VW 1.6 diesels all over the place
Isuzu Boxtruck, Ford Backhoe, all running on biodiesel
Needs diesel lawnmower & chainsaw

mobile_bob

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Re: engine mounting v 4.0
« Reply #4 on: December 21, 2006, 03:48:57 AM »
i c no reason that it would not work, provided the mount block is of sufficient weight to start with.

for instance if you had a mount block of perhaps 6 inches thick and large enough in length and width to encompass and mount not only the engine
but the genhead and related equipment, the end result would be a slab of perhaps a ton

just an idea, one of many :)

bob g
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Doug

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Re: engine mounting v 4.0
« Reply #5 on: December 21, 2006, 04:10:34 AM »
I know what you thinking Bob I thought about it too.

I have two choices, the block on the rock or the block in the soft wet clay.

The rock will require some bolting. The clay will require a deep pilon because of frost ( six feet deep )

I though about an inverted 60 for a wider foot print and better energy transfer.

No matter what this can't go in my basement so I'm in a different boat than you.

Idealy what we need is a better roid, seriously...
Or a crank driven counter weight spinining anti clock wise to the crank to dampen vibration and a harmonic ballancer to burn of some twist in the crank.
Way off topic, and out of reach....

Flubber, thats what we need Flubber isolation mounts for the block....

I'm grasping

Doug

mobile_bob

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Re: engine mounting v 4.0
« Reply #6 on: December 21, 2006, 06:14:44 AM »
Doug:

(this is my 4th typing of this post,, hopefully it will post this time)

it occurs to me that perhaps we are looking at mounting from the wrong perspective.

the question then becomes from what perspective should we be viewing the problem (assuming it is a problem)

we need to limit movement of the engine? yes. but...
do we need to limit the whole engine? no,,,
 or a particular part?  yes, that part being the crankshaft

we have three planes to work in and 6 ranges of motion, plus the rocking component

the rocking component is the hardest to address if we think inside the box, and use the commonly accepted mounting method where the
crankshaft centerline (c/l) is well above that of the mount. further the rocking component is worst at critical speeds (that rpm during spin up and spin down that the engine lurches around very pronounced)

so going back to the crankshaft c/l viewpoint, how do we reconcile the rocking motion or make this motion a non factor?

by building a steel frame mount that is U or cradle shaped, where the engine is bolted rigidly to the bottom of the U/cradle and
the rubber mounts are attached at the top of the U/cradle legs, inline with the crank  c/l plane, and where the crank c/l is in the
middle of these mounts. this way the rocking motion becomes no factor as it rotates around the crankshaft c/l by design.

we are then left with the three planes of movement and 6 ranges of motion

the vertical plane (up/down) can be addressed effectively by varying the thru bolt torque of the donut rubber mounts, effectively limiting the
up/down motion to within the design parameters by tuning in under operation.

this now leaves the other two planes and 4 ranges of motion, this is where the steel cored donut mounts really shine in that they have sufficient surface area
and contact area with the steel components to limit these two planes and related motions by design.

another part of the donut style mount is the top washers that are used to limit torque action or in this case limit travel during the aforementioned critical speeds of the
engine.

this will work!

i am now convinced that i can design a steel frame mounting system that is resiliently suspended, that does the following

1. makes the rocking component a non factor (+/- .005 or less)
2. limits the vertical motion component, to within whatever parameter i want (+/-.005-.010")
3. limits the fore and aft component, to well within  (+/-.005-.010")
4. limits the side to side component to well within  (+/-.005-.010")
5. provides for critical speed snubbing,
6. provides isolation from the concrete floor and the related structures.

ok,, GuyF. i know you are out there,,, poke this one full of holes! :)

this mount would be superior even to a concrete block that has some movement in a clay bed, where rocking motion is evident.

bob g
otherpower.com, microcogen.info, practicalmachinist.com
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Doug

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Re: engine mounting v 4.0
« Reply #7 on: December 21, 2006, 06:46:32 AM »
Sounds like you found a technical paper I also read regaurding the U frame idea and moving the " Foundation " support closer to the crank....

I wish I could sleep....

Your probably on the right path from an isolation perspective but I can't get the idea out of my head that guy planted about reducing crank shaft stress and another article I read about vibration induced by mounts and bearing failure.

I don't know.

I got a fly wheel with pits in it on my mind right now Bob.
Vibration aside I just might scrap the engine and call it a day....

Doug

mobile_bob

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Re: engine mounting v 4.0
« Reply #8 on: December 21, 2006, 07:17:51 AM »
Doug:

i can relate to the sleep thing,, i finished my last post, went to bed, fell asleep and then woke up thinking about this damn mount thing.

i am a sick, sick man.... :)

as far as your flywheel on the petter, i wouldnt scrap it,, it is pretty much a solid unit, and likely won't fail catastrophically

yours is far less a worry than the listeroid one we saw today.

i say ,, paint her yellow and let her rip!

as for finding the tech paper, no i havent,,, i have just been thinking about this issue for months now.
and i caught a bit of the show "criminal minds" tonight,,, and the brainiac, stated "perhaps we are looking at the problem from the wrong perspective"
that caught in my head, and i went back to the drawing board and rethought the whole system and what we are trying to control movement on, that being the
crankshaft.

the logical progression was in how to limit motion of the crankshaft in the 3 planes , as viewed from the center of the crankshaft.
the rest fell into place once i got my head around thinking from within the crankshaft c/l


bob g
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Guy_Incognito

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Re: engine mounting v 4.0
« Reply #9 on: December 21, 2006, 09:13:15 AM »
Is there an echo in here?

http://listerengine.com/smf/index.php?topic=1097.msg14311#msg14311

 :D

I know everyone tells me that movement of the engine / generator is a bad thing, but I still think that it's of little importance.
I've mentioned the reasoning why before - regarding the orbit and forces of the crankshaft around the centre of mass in an unbalanced system - so I've pretty much said my piece.

All I'll say now is if you let your engine move a little in relation to the rest of the world it becomes a lot easier to reduce the transmitted thump. The more you let it move on it's mounts, the less force is transmitted to the outside world. Whether that's an important criteria for you is up to you alone I guess.

mobile_bob

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Re: engine mounting v 4.0
« Reply #10 on: December 21, 2006, 05:39:36 PM »
GI:

i remember your post now, but the difference is in the purpose of the U design

at 8.5 inches (from your post) you provide clearance for spring and shock mounts,  and lower the center of gravity which is fine,

but what i am talking about is moving to approx 12.5 inches, not because of lowering the center or gravity
or to provide clearance but to get the rocking element to be at the crankshaft centerline.

and you are correct in your assessment, in that the more you isolate the more movement you will have and visa versa

you run into that with automobile's, and shock absorber, spring selection and location.

bob g
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danalinscott

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Re: engine mounting v 4.0
« Reply #11 on: December 21, 2006, 06:53:08 PM »
In an "echo" from the post GI linked to (mostly to determine if I am upt to speed myself)

The engine without the counterbalance built in to the flywheels will tend to hop up and down and fore and aft due to the movement of its piston/connecting rod and crankshaft masses. The counter weighting cast into the flywheels should (theoretically) be able to counter most of the up and down movement..but cannot counter the induced ratation since they would have to counter rotate to do so. And due to the questionable quality control inherant in the loose association of foundry/machining/assembly companies that "make" these engines in most cases the counterbalancing will only be approximate at best. Since a flywheel that is even a degree of in its relation to the crankshaft will never functionas intended the only way to assure that the counterbalance function is opertainting as the engines designers intended is probalby to get blank flywheels and machine them to a more exacting standard. If someone with the equipment needed to  do this began selling them I do not think I would be alone in beating a path to their door with cash in hand.  (Please...someone say "foolish Dana...someone already DOES!" and provide a link)

Lets assume that is not an option though and we have to make do with flywheels which are only "in the ballpark" as far as counterbalancing ability goes. At least on a single cylinder listeroid (twins will be trickier) if the flywheels are "matched" to each other as closely as possible so the counterbalances are of equal weight and that weight is indexed to the crankshaft as close to identical as possible.

 Is it not mainly the variations in the counterbalance forces of the flywheels that induce rocking and side to side motions? A well balanced engine should be much simpler to "tame" than one with imbalance "issues".

Does it not make the most sense to reduce as much as possible these unwanted forces/motions as part of the basic procideure leading to initial run up of the engine?

I realize that I may be stating the obvious and there may be a post on how to balance and (possibly even) index flywheels somewhere in the archives. I have seen this subject mentioned several times..but have found no such post. However I am new here.
If there is such a post would someone mind directing me to it? I have a knack for missing the obvious. ???

Moving on...let's assume that the counterbalancing of teh flywheels has been made as effective as possible.
In which case the "kindest thing" I think we can do to th engines bearings  are to allow the remaining movement to go on unempeded. This should minimize the forces applied to them. But these are very robust..and probably capable of withstanding more abuse than making the engine completely immovable exerts on them.  i do nto think they need any knindesses beyond  receiving adequate lubrication. And they are easily and inespensivly replaced. This is of course only a "funugis" opinion and nothing more.  ;D  As is the following:

Doesn't the least amount of wear on the engiens bore, rings, and generator head bearings occurr when they are held rigidly in the same "space"? Doesn't this wear increase progressivly with the amount of movement from a fixed point in space they experience?

What about the exhaust pipe (if more than a peppercan is used) connection?

I believe that a little movement is unavoidable. But I also believe that the immovable object method of mounting listers is due to the fact that when one is looking at a 10-20 year (or longer) working life the cumulative effect of little motions on engiene and aux. parts may be significant. For those who do not expect to run 24/7 or even 2200/365 this may not be significant enough to worry about.  But for those who do (and I am one of them)  I am afraid that the secondary effect of not using a "immovable object" mount may be unacceptable. Which..considering the position it puts me in is also unacceptable.  I want the best of both worlds.  ::)

But I only see one way to achieve that.....a counter rotating mass counter balance.
Which unfortunately seems too complicated a project to even begin a discussion on at this point.

Yeah..a little movement may have to be accepted if a concrete block is not employed.

Effective movement snubbers may be the only simple solution.
Are you guys aware of phase change gels? They have the property of going solid when force is applied and back to gel once it is removed. The change can be very rapid and might be applicable here.  My hunch is that they would avoid the "spring back" problem with any elasomeric doughnut or spring incorporated in an engine.

I'll shut up now. I have probably strayed far off topic by now.
Probably would have been better off not opening my mouth.
(Huge sigh from the group amid whispers of "I thought he would never shut up...dumbass!")



Dana
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Guy_Incognito

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Re: engine mounting v 4.0
« Reply #12 on: December 21, 2006, 10:10:33 PM »
i remember your post now, but the difference is in the purpose of the U design

I know, I was just stirring ya  ;) - I did mention 8.5" - that's the height of the bare mount - but I was aiming for the machine to be suspended at about the CG height whatever that ended up being.

I thought that in a resilient system, the rocking moment would be around the CG regardless (whereever that may be) as opposed to crankshaft centreline? The forces emanate from the crankshaft, but when they are applied to the machine, they'll simply attempt to pivot the engine about the CG, correct? So following from that, if you can line your CG up with your crankshaft, there's very little arm for the forces to work on and rocking should be minimised.

Or maybe not. It's 8am and I've just come home from another long night shift.

Quote from: danalinscott
I'll shut up now. I have probably strayed far off topic by now.
Probably would have been better off not opening my mouth.
(Huge sigh from the group amid whispers of "I thought he would never shut up...dumbass!")

Don't stop now, if we all kept our mouths shut, a lot of interesting stuff would have been missed.

Flywheel balance was a hot topic, until we went all crazy with the resilient/concrete mount holy war. There's quite a few threads - I think the "balancing out the bounce" one had some good detail in it. There's been posts of two flywheels on the same engine being more than just a few pounds different.... just another issue to contend with.

Don't really know about wear on the bores/etc. It might be low enough to be negligible, considering that plenty of 'mobile' engines get rattled about in all sorts of orientations on considerably more flexy mounts. One of the more interesting designs I was considering was to simply only suspend one end of a modestly long frame near the engine, and hinge the other end near the genset. The hinge prevents a lot of movement in all axes (if designed right), allows the gen head movement to drop proportionally due to the length of the frame, yet most of the engine jiggle is still isolated by the suspension at the other end. Things such as exhaust, fuel hoses, wiring,etc could be brought out at the hinge end, greatly reducing their movement/flexing. In fact, the more I think about this design, the more I'm inclined to try it out.....

An internal counter-rotating balance shaft would be a little beyond my engineering skills. But a timing belt from the inside of the flywheel to a counter-shaft close by on the frame/crankcase is doable... and it would be relatively easy to time by the seat of your pants. (A tooth back and forth till you found something with the minimum movement, increase counterweight until least movement seen) ;) But of course, that's still more whirling , threshing parts to fail on you. All this work doesn't dampen the movement from the torque impulses though.

The advantage of having a resilient mount is that you can see your improvements in balance directly. It's a little hard to tell if your moving your 2 ton block 0.0003" or 0.00025" when you're tweaking it. And I'll restate my concerns about someone uncrating a new engine, bolting it to the standard block (or more, as more mass is better, right?), and never knowing that he's got a hideously unbalanced machine until some rotating part rips off at speed.

(damn fsocket errors! for those of you that don't know - when you've finished typing your message and your cursor is still in the edit box, type ctrl-a then ctrl-c. Then if it fails and eats your post, you can just repost again, put your cursor in the blank message box and press ctrl-v to get your message back to where you had it.)
« Last Edit: December 21, 2006, 10:16:07 PM by Guy_Incognito »

mobile_bob

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Re: engine mounting v 4.0
« Reply #13 on: December 22, 2006, 02:49:31 AM »
GI:

we are not concerned with center of gravity, as it is likely well above the crank centerline.
for example

if we find the center of gravity and suspend the engine at that point we then have the crank centerline below this point,
thus when the rocking component is factored in the crankshaft will move in an arc.
now if we set the mounts inline with the crank centerline, the engine can be free to move as far as it likes in the rocking motion
with no effect or movement on the crankshaft or flywheels as now they are in the pivot point of the arc.

automotive engines are designed this way, the front and rear mounts are located so if you draw a line between the centerlines it will intersect in the center of the
crankshaft. the engineering books have numerous reference to this.

the lister is easier in this regard as the crankshaft is level unlike the downward slant of an automotive crankshaft.

the parts that we want to control stresses from movement are the crankshaft, flywheels, and main brgs (because they deal with supporting these parts), all other parts
while rotating around this pivot point due to rocking don't have detrimental stresses applied to them, (provided of course we are talking a small amount of movement and not a 1/4 turn!)

as far as the rocking moment, we can't do much about that, the engine will always have a rocking moment no matter how we mount it, but we can design to place the center of this moment where we want it,,, and the centerline of the crankshaft is much preferred to the center of gravity or center of mass.

i need to get a scanner and figure how to post pics, so i can put up some reference diagrams and pictures.

i know sometimes my expanation leaves much to be desired, and a picture is worth a million key strokes :)

Dana:

don't ever feel like you need to shut up!

it is thru the open exchange of idea's and thought that much is learned.

sometimes the simplest of question's starts a debate which brings forth all sorts of interesting and pertinent information.

besides some of our debates on this forum are down right entertaining, and yes sometimes even "knock down drag outs"
with name calling, sand kicking, screaming and yelling,,,, just like a family :)

wouldnt be much fun if we didnt ruffle some feathers once in a while.

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Guy_Incognito

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Re: engine mounting v 4.0
« Reply #14 on: December 22, 2006, 04:24:26 AM »
Quote
if we find the center of gravity and suspend the engine at that point we then have the crank centerline below this point,
thus when the rocking component is factored in the crankshaft will move in an arc.
now if we set the mounts inline with the crank centerline, the engine can be free to move as far as it likes in the rocking motion
with no effect or movement on the crankshaft or flywheels as now they are in the pivot point of the arc.

Aha! Gotcha. Didn't seem quite so obvious this morning... but it's a little bit more obvious now after a bit of sleep. :D