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Author Topic: engine mounting v 4.0  (Read 77312 times)

Doug

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Re: engine mounting v 4.0
« Reply #30 on: December 23, 2006, 07:03:59 PM »
I think I see a flaw in your plan Bob:
Lets for a moment assume the 660 pounds for a min....

If you have that force directed down by ignition before its ever translated into torque you get an equaly up ward push from the engine and foundation. The rubber mount is going to let the engine compress between the block and give you more movement. Most of the energy stored in that rubber will be released into the block and the engine case. The block energy hopefuly will be dampened but the earth the engine case engery I don't know. This gets more complicated as the crank rotates threw the stroke and the presure drops.

Not all of this 660 force is directed up and down and everything changes as the angles between the force vectors, resultants andf torque changes. Way above my ability to finger out....

Uhm about all I can say it things jigle, the jigle won't be helped by rubber but will issolate some fo these forces in the engine case rather than disperse them in the ground.

Doug

mobile_bob

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Re: engine mounting v 4.0
« Reply #31 on: December 23, 2006, 11:46:32 PM »
Doug:

you are correct that there is an equal force going up as there is down, all of the forces are contained between the head and the main brgs, at least as far as the up/down vector.

or rather i should say the vast majority of those forces,

the only things transmitted outside the block are

1. torque action

2. imbalance issue's with the engine

3. sound, vibration of ignition

also it is good to note that in 99.999% of concrete mounts they are still resilient as the ground has some give, some ground obviously has more give (damp clay)

if there were any real down force's they would abraid or work the concrete to death at the mount points.

my contension is basically if we had a steel ball, with a shaft welded on it
and cast the shaft into a concrete block and then set off a bomb withing the steel ball we would not have a very large down force if at all,
but we would transmit sound, noise or whatever you want to call it. certainly not a 600lb hammer blow

the mounts i referenced to are common mounts used for all sorts of hd truck engine's, most everyone uses them, are as common as dirt.
they last forever in very hostile environments, and handle torques in excess of 50 times that of a 6/1 comfortably.

with the diagram example i was only trying to illustrate how to limit the one component that is common to all engine's, that be torque and anti torque actions

we can limit that rocking action by simple design, leaving us with only
the up/down, and the side to side action

these rubber mounts are very dense, and only about 3/4" thick when torqued, the shear strength is such that the engine likely will not move fore and aft, or side to side but very little, leaving only the up and down component, which is very small in a well balanced engine to start with

the up/down, side to side, and fore/aft movement are far smaller components than that of the rocking component due to torque and antitorque action.

the up/down is going to be the sound transmission plane, so balanceing the engine should be done first to reduce what needs to be mitigated, whats left the rubber mounts will isolate quite well.

good mounts on a cat, cummings or whatever do a really nice job of isolating the noise/sound from the engine to the cab, but when one does wear out and fall out, the engines will damn sure rattle your teeth out.

if anything the truck mounts might be too stiff, and as such not isolate as well as a softer mount.

just like everything else in life, it is a comprimise.  less movement more transmission, more movement better isolation.

i like the truck mounts because i can torque the thru bolt to fine tune to an acceptable comprimise between little movement and good isolation.

i still say that eliminating the rocking components effect on the crank/flywheel/brgs,  is a huge step in the right direction

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

Doug

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Re: engine mounting v 4.0
« Reply #32 on: December 24, 2006, 01:51:59 AM »
No real argument here Bob....

My heads not so clear right now, I'm full of beer pork and venison....

But i didn't over do it!

I need to reflect on these ideas for while...

I looked at a set of cab mounts for Wagner truck and considered them as motor mounts. Yes they are large strong and look like they would last for ever as mounts for a Lister.

I need to look at a force vector diagram of an engine, even then I'm not sure I can get all the forces and resultants straight ( starting to get over my head )

Doug

hotater

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Re: engine mounting v 4.0
« Reply #33 on: December 24, 2006, 02:00:35 AM »
I got over my head the first couple of post a year ago!!   Enough concrete works.    ;D

I'll leave it up to the engineers to figure out how much is enough.  Forty sack worked for ME!!

.........and I'm DONE.  Ya'll are still calculating and figureing.    ;D ;D

Merry Christmas!
7200 hrs on 6-1/5Kw, FuKing Listeroid,
Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.

Doug

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Re: engine mounting v 4.0
« Reply #34 on: December 24, 2006, 02:14:04 AM »
Its no longer a question of what works but a question of how and why...

I've learned so much about general machine theory that aplies to my day job its not realy a question of how much any more I want to be able to look at foundations and decide for myself things about them. There is a pair of 500 hp fans near my shop that vibrate a lot. They trip the monitors from time to time. More concrete is not he answere the foundations are wrong.

Doug

mobile_bob

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Re: engine mounting v 4.0
« Reply #35 on: December 24, 2006, 02:38:02 AM »
Tater: you ole trouble maker you,, merry christmas to you too :)

some of us aren't in the position to live the dream yet,,, darn it,, some of us (me) have to live vicariously through folks like you.

as for the forever debate on this topic, for me it is an expanded learning thing, i like the theory.

and truth be known, i will probably use the 40 sacks in the end anyway,,, but maybe not :)

(actually i am only in this discussion to drive you concrete guys crazy... hehehe)

but seriously i have arrived at the formulae and tons of reference to how to specifically engineer a concrete base as well through all this
ongoing debate and hairpullin.

just figured i would fully investigate all the alternatives as well.

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

Doug

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Re: engine mounting v 4.0
« Reply #36 on: December 24, 2006, 03:02:19 AM »
These pictures suplied by Peter are of some Nordberg engines some using the mounting principle Bob sugests other mounted more like what we are doing withthe Listers now

http://www.oldengine.org/members/diesel/Nordberg/Nordberg3.htm

This Petter Atomic is sort of a cross between the two. I'd like to know where the CG is on this engine.

http://www.internalfire.com/albums/album30/tx.jpg

DOug
« Last Edit: December 24, 2006, 03:18:23 AM by Doug »

Guy_Incognito

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Re: engine mounting v 4.0
« Reply #37 on: December 24, 2006, 04:27:59 AM »
This Petter Atomic is sort of a cross between the two. I'd like to know where the CG is on this engine.

I think it's somewhere in the next room  :D

hotater

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Re: engine mounting v 4.0
« Reply #38 on: December 24, 2006, 04:29:34 AM »
I understand the wish to theorize...thats' how things get invented and how problems get solved.  
I'm the type that would rather burn myself welding something together than burn out a 'mental math breaker' trying to calculate what would actually work better.

IF I were to build a moveable Lister mount it would be a 3x6 foot box made of ten inch channel iron.  It would be made plain side out and braced for a heavy floor and rails for the engine.....and then poured full of concrete.   THEN I'd figure out what's the best material to use between that and the floor to isolate any vibration.

Maybe surplus breast implants??    ???
7200 hrs on 6-1/5Kw, FuKing Listeroid,
Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.

Doug

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Re: engine mounting v 4.0
« Reply #39 on: December 24, 2006, 04:53:51 AM »
Jack that is probably the most inovative idea for mounts yet. And they're designed with "jigle factor"....

Dave I wish I had that Petter semi diesel in the next room

mobile_bob

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Re: engine mounting v 4.0
« Reply #40 on: December 26, 2006, 12:52:53 AM »
well got the kid back to her mom today, and had the day to sit back and relax abit.
and well you know, i can't sit still for long without all this stuff rearing back up in the dark
recesses of my brain, so here i am again.

i question very strongly the assertion that there is a strong vertical component from ignition from the power pulse of a lister

the reason i question this is based on observation of a 12hp changfa, which is a horizonal or lay down cylinder, i have one sitting on a plywood skid in my
shop, and i can start and run it at idle ~1000rpm (by ear) and it will not move across the floor. this tells me that the force from ignition is contained within
the crankcase and the only thing being tranmitted to the mount are the torque and antitorque and the sound transmission thru the mount to the floor, which i
can feel in the house (much less so if the plywood skid is set upon a rubber mudflap)

so i am left to ponder if the changfa has no movement opposing the ignition forces, then why would there be a significant downward component from a lister?

if all one needs to control is movement on the crankshaft due to rocking, and we can handle that with design, and there is a very small or non significant vertical
component, then the rubber mounts such as described should provide the amount of isolation necessary to limit the transfer of sound/vibration of ignition to the
concrete floor.

i need someone to step up and argue opposition to this view

GuyF, you out there?

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

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Re: engine mounting v 4.0
« Reply #41 on: December 26, 2006, 01:45:47 AM »
A piston / cylinder / crankshaft arrangement is pretty much a closed system with respect to reciprocating movement getting out - all the combustion forces are balanced internally near ignition/TDC by the piston/conrod/bearings/cylinder/head.

As the gases expand and the piston moves down the cylinder some of the force is translated to rotation (and vice-versa on compression) which gives you the torque/antitorque pulses. The only reciprocating force escaping from the engine is the static imbalance between reciprocating and rotating masses - which is what, equal to a few kilos oscillating up and down the stroke at 650RPM?

One wonders if the traditional "thump" from concrete-bound listers is actually a rocking component of the concrete block getting sent out as opposed to the assumed vertical-lift-style thump. Hence the spec for a relatively deep block as opposed to a shallow slab floor with the same mass. The slab, with a rocking motion generated from the engine, would raise and lower the outer edges of the block a fair bit more and more easily transmit thumps than a block mostly underneath.

I wonder how that "V"- shaped rubber-lined concrete block would go if you set the v-edges to be perpendicular to the applied rocking force as much as possible.

Doug

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Re: engine mounting v 4.0
« Reply #42 on: December 26, 2006, 02:12:16 AM »
Bob was thinking about the inverted V in one of his posts.

I don't think the Asian horizontal diesel is a good analog for a Lister. Shorter stroke smaller lighter pistons and the Asian horizontal has two counter rotating ballance shafts. That much said some do not, I know of one that vibrated like the buisness end of an atomic jack hammer for about 12 hours before it self distructed. That was a bad engine from the start, but the owner said the vibrations and for aft shake was real trouble.

Doug

mobile_bob

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Re: engine mounting v 4.0
« Reply #43 on: December 26, 2006, 03:02:54 AM »
GI:


i agree that the forces are contained, that i have always understood, but i have seen reference to some figures of a 660 lb down force from
ignition from a lister, i wonder now whether the reference did not understand that this force is not the force down on the mount,whether concrete or
whatever.

i do wonder though whether the thump that is transfered is mearly a sound transfer of ignition, and not a mechanical movement.

for intance, you can hold a rod up to your ear and tap it perpendicular to the rod axis on the other end and quite clearly get the transfer of sound
but no transfer of force. so if there is no transfer of force then rubber should dampen the sound transmission.

so we seem to agree that perhaps the rocking component is the primary transmission component to the ground.
 so it would follow anything we can do to reduce the rocking component or control it thru design the less there is to transmitt motion
 and thump to the concrete floor and other structural elements.

of course you are correct that if we have any static, and particularly dynamic balance issues they will certainly be transmitted to the base as well.
which lends validity to getting the engine as well balanced if not dynamically at least statically. the better the balance the less these unbalanced
forces come into play obviously.

i am not sure that the cube base would work better than a slab base (concrete), on the one hand any rocking would lift a longer base further, but it would take much
more torque to do so (from a leverage standpoint)

"I wonder how that "V"- shaped rubber-lined concrete block would go if you set the v-edges to be perpendicular to the applied rocking force as much as possible."

now that is an interesting concept "geometrically", the length of the block would then dictate the angle of the V shaped base, to keep the sides of the V perpendicalar
to the rocking radius. i will have to think about that one.

Doug:

good point as to the counter rotating shafts, they work together to help to balance the rotatating assembly, but
they cannot work to overcome any forces of ignition because those are not static, rather those forces change with loading

also i do have a non countershaft changfa, and it does not seem to exhibit motion in opposition to the piston downforce either...


onward:

what i do find is a thump transmission from the changfa sitting flat on the concrete slab, i think i will run a few crude experiments to
see if i can isolate the "thump" or mitigate it.

basically i will just pickup the assy and sit it down on a group of rubber isolators, and see if the thump is mitigated, if so
then i think the next step will be to build a "cradle style subframe" to center the rocking element on the crank c/l
and then mount the subframe on rubber mounts, and do some testing.

i guess the beauty of this forum is the diversity of approaches, it damn sure would be time consuming and cost mega bucks to design, build and
test each an every approach.

because i have the changfa on the floor and all the related parts and stuff to assemble it, i think i will now go forward and try the cradle method or resilient mounting.

if the results are what i anticipate, then perhaps the next will be the same design of mount with a 25/2 lister.

we all know that 2 tons of concrete works, and some folks have done well with a ton of crete,
we also know there are some that have had good results on large wood beams,
i guess i will go the mile and do the cradle/resilient mount, and see what the result is.

bob g



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mobile_bob

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Re: engine mounting v 4.0
« Reply #44 on: December 26, 2006, 03:47:29 AM »
GI:

i just ran the geometry, and it would appear that the angle would change (in an effort to keeping perpendicular) with the length of the concrete block
as it applies to a V mount.

looks to be an interesting mounting system, with enough mass so as to be very hard for the engine to lift either from rocking or vertical lift(balance issues)

would be interesting to give it a try, but sadly an expensive experiment, i think i would want to try and prove out the concept a bit more before
i expended the effort to casting a V pocket in the floor, and then rubber lineing the sides and casting the machine base.

one thing i am sure of the quality of the subsoil would have no real effect on the outcome.

might be an interesting alternative for those on questionable soils, damp or wet clay, etc.

in the future i plan on a shop, so i would probably try this mounting system in that environment.


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