concrete vs resilient mounting round 2

[Procrustes]

In the "seeking an answer" thread, I recently posted my reasoning for why rigid mounts are better than flexibles.  Few are intrepid enough to wade to the bottom of that one, so I'll repeat myself here.

I believe that most rigid materials degrade non-linearly with stress.  Here's a representative graph of 'brittle aluminum' from wikipedia:


For example, this sample can withstand about 10,000 cycles at 150 MPa stress, but not even one cycle at twice that.  Imagine tapping a glass bottle lightly with a hammer ten times, versus once with ten times the force.  The bottle may remain intact in the first case but shattering under the heavier blow.

With flexible mounts the engine as a whole has a particular acceleration at every point in time.  Given the inherent problems in balancing a one-cylinder engine, this acceleration will be acyclic.  Sometimes the engine's acceleration will offload stress onto the mounts, but other times it will produce an unusually large and compromising stress.  For instance, the engine as a whole could accelerate upwards during the powerstroke and thus create a stress spike in the crankshaft.

[mobile_bob]

Pro:

it is late so i might be a bit "thick" just now, but

" For instance, the engine as a whole could accelerate upwards during the powerstroke and thus create a stress spike in the crankshaft."

why would the engine accelerate upwards on the power stroke?


perhaps i am missing what you are trying to support or rather assert.

proper crankcase design (which lister follows in a very classical way) contains all stresses generated within the engine.
only torque action, or antitorque action and vibrations are transmitted outside the crankcase no matter which mounting method you choose.

when ignition takes place you have forces working in two primary ways, one is trying to lift the head off, the other (opposite reaction) is trying to stuff the piston thru the floor, the crankcase contains and manages these stresses, these stresses are the most severe and cyclic stresses placed on an engine and it makes no difference to what it is mounted to. poor design here, means blown head gskts (minor), broken bolts (not so minor) to broken crankcases,failed brgs, broken rods or crankshaft, all by the way are design defficiecies, which lister did not have and listeroids have not shown to have. so clearly the design is proven and sound from and engineering standpoint.

the only thing transmitted from ignition are shocks/vibration of the combustion process, which follows vectors straight thru the tapered crankcase into the concrete block, steel frame or mud pie you bolted it down to.  while these stresses can be significant, they have never been an issue with listers, mounted to all sorts of things, and have not shown to be a problem with the listeroids. this is mainly because of the use of cast iron and steel instead of materials that have a finite lifecycle.

i am not sure where you are going with this, or where you would like to go with it.
it has become quite clear that lister spec's all sorts of concrete bases, from 600 lbs to well over a ton, steel bases, cast iron bases, and even mention the use of resilient mounting, none of which have a history of detrimental effect on the longevity of the engine from a catastrophic failure, such as broken crankshafts or cases.

are you saying that listeroids will manifest these problems if not mounted to concrete? if so please explain how and why? with some solid evidence or references

cyclic charts of different metals are all well and good, but i think you would agree that how a material is used, and in what quantity along with actual stresses imposed clearly show that if engineered properly  catastrophic failure is dramatically reduced to the point (in the case of a stationary engine) as to not even merit mention.

surely you are not trying to support you position useing a chart on aluminum where a sample piece is subjected to a bending force and cycled to failure, when an engine that is soundly engineered not only has no such bending force imposed but is made of cast iron and steel (which chart out dramatically different than aluminum even in sample pieces)

i can't remember but someone posted something to the effect

"show me two failed crankshafts due to mounting, and i will look at it, show me 4 and perhaps you have a trend..."

so far i have heard of only one broken listeroid crankshaft, and that was reported to me by a dealer in these engines, after selling hundreds of these things.

one broken crankshaft does not a cake make!

i would even go so far as to state that if that broken crank was analized it would show a flaw either in the metallugy or a flaw in the fillet area not being ground properly.

these engines being built as heavy as they are, and at relatively low power densities literally cannot break themselves (if there was not a flaw to start with )  running under rated load/rpm etc.

so what are you saying?

bob g

[Procrustes]

" For instance, the engine as a whole could accelerate upwards during the powerstroke and thus create a stress spike in the crankshaft."

why would the engine accelerate upwards on the power stroke?

If it's not accelerating cyclically on its mounts then it will be have an essentially upredicatable acceleration at a given time.

perhaps i am missing what you are trying to support or rather assert.

proper crankcase design (which lister follows in a very classical way) contains all stresses generated within the engine.
only torque action, or antitorque action and vibrations are transmitted outside the crankcase no matter which mounting method you choose.

when ignition takes place you have forces working in two primary ways, one is trying to lift the head off, the other (opposite reaction) is trying to stuff the piston thru the floor, the crankcase contains and manages these stresses, these stresses are the most severe and cyclic stresses placed on an engine and it makes no difference to what it is mounted to. poor design here, means blown head gskts (minor), broken bolts (not so minor) to broken crankcases,failed brgs, broken rods or crankshaft, all by the way are design defficiecies, which lister did not have and listeroids have not shown to have. so clearly the design is proven and sound from and engineering standpoint.

You're right, the crankshaft example was stupidly wrong.  I don't cede my argument though.  I feel certain that a  given Lister will fail sooner if suspended from a spring than if it were affixed to a block.  Most any other kind of mount is a gradation between these two.

the only thing transmitted from ignition are shocks/vibration of the combustion process, which follows vectors straight thru the tapered crankcase into the concrete block, steel frame or mud pie you bolted it down to.  while these stresses can be significant, they have never been an issue with listers, mounted to all sorts of things, and have not shown to be a problem with the listeroids. this is mainly because of the use of cast iron and steel instead of materials that have a finite lifecycle.

You really believe that vibration is not an issue with Listers?  No doubt you will use wooden stakes and rope to mount yours (I hope this doesn't sound as snide as I suspect it does.  Couldn't think of any other way to say it).

i am not sure where you are going with this, or where you would like to go with it.
it has become quite clear that lister spec's all sorts of concrete bases, from 600 lbs to well over a ton, steel bases, cast iron bases, and even mention the use of resilient mounting, none of which have a history of detrimental effect on the longevity of the engine from a catastrophic failure, such as broken crankshafts or cases.

are you saying that listeroids will manifest these problems if not mounted to concrete? if so please explain how and why? with some solid evidence or references

I'm saying Listeroids will be more inclined to stress fractures as they are less rigidly mounted.

cyclic charts of different metals are all well and good, but i think you would agree that how a material is used, and in what quantity along with actual stresses imposed clearly show that if engineered properly  catastrophic failure is dramatically reduced to the point (in the case of a stationary engine) as to not even merit mention.

You are saying that concrete is better, but insignificantly so.  That sounds fair to me.

surely you are not trying to support you position useing a chart on aluminum where a sample piece is subjected to a bending
force and cycled to failure, when an engine that is soundly engineered not only has no such bending force imposed but is made of cast iron and steel (which chart out dramatically different than aluminum even in sample pieces)

Cyclical bending forces are precisely what the crank, flywheel spokes, etc see, right?  I don't understand this objection.

As for iron vs aluminum: non-linear fatigue is non-linear fatigue, whether it's in aluminum or steel or iron or glass.  A rigidly mounted engine can't normally creep beyond a certain point in the fatigue curve, whereas a flexibly mounted engine might.

i can't remember but someone posted something to the effect

"show me two failed crankshafts due to mounting, and i will look at it, show me 4 and perhaps you have a trend..."

so far i have heard of only one broken listeroid crankshaft, and that was reported to me by a dealer in these engines, after selling hundreds of these things.

one broken crankshaft does not a cake make!

i would even go so far as to state that if that broken crank was analized it would show a flaw either in the metallugy or a flaw in the fillet area not being ground properly.

these engines being built as heavy as they are, and at relatively low power densities literally cannot break themselves (if there was not a flaw to start with )  running under rated load/rpm etc.

so what are you saying?

It's not impossible to see fractures in a Lister, that's all you have to accept to see that the block is better, no matter how slightly.

And, what if your engine does have a flaw?

[Guy_Incognito]

Lets look at it another way. I've mentioned this in other posts, but I'll mention it again. I'll step through it:

All the imbalance forces are transmitted via the crankshaft to the engine via the bearings. I know, there's reaction forces on the head,etc as well , but these are present regardless of what mount you've got. So pretend, for simplicity, that you've got a static imbalance in your flywheel and just the flywheel and crankshaft are rotating freely suspended by a set of springs on each end. When spinning, the centreline of the crankshaft will scribe out a circle, the centre of which is the centre of mass of the whole crankshaft/flywheel assembly. This difference between the centreline of the crankshaft and the centre of mass is the source of all the vibration in an engine. (Combustion forces also act as the same as a weight on an arm and shift the apparent centre of mass when they occur.)

Now, if by some amazing feat of engineering, if you could make a mount that shifts the engine around in a circle that exactly matches that which is scribed out by the centreline of the crankshaft, you would have pretty much zero load on the bearings, crankcase,etc. We'll call this the "ideal motion" of the engine.

Further to that, it stands to reason that the further away you are from that ideal motion, the more force is applied to the bearings. So as you progress from very springy springs, to rubber mounts, to concrete blocks, the further away you are from that ideal motion and the more force is applied.

Ok, so build the engine around those bearings, suspend it on very springy springs and run it. How much force is needed to tow that 500kg of engine around? A reasonable amount, no doubt. The forces are there because the engine lags the applied force by a certain amount, and thus you are a little distance away from the ideal motion of the engine. Again, if you had some wonderful arrangement of gears and cams and could shift your engine in a circle matching that of the crankshaft, there'd be no forces applied.

Now, same as above, with a lightweight frame attached to the base of the engine - how much force is needed to tow that frame around in a cyclic fashion? Same as with a bare engine, plus a bit more to pull the mass of the frame about.Not very much more, it's a pretty light frame.

Set the engine on concrete, bolted down firmly. How much force is needed to budge that concrete? Well, following on from the above examples ,you're now at the maximum distance away from "ideal motion" of the engine, as the engine cannot move very much at all. So maximum loading is now applied to the bearings/crankcase/mounting bolts,etc.

Make sense? It sort of does to me 

[mobile_bob]

i am not saying that mounting to concrete is better than any other mount, just as i am not saying that mounting to something else is better than concrete, although
i can make the case that concrete returns and in some cases amplifies the shocks, vibration and stresses imparted upon it back to the engine.

also please note, that even if bolted to a concrete block it is still on a resilient mount albeit a very stiff resilient mount, (unless you cast you crete ontop of a granite bedrock)

you seem to take to the tangent and extremes to support your position

i don't support spring mounting the engine or any engine, and don't know anyone that would
there is such a thing as an engineered resilient mount, that does the isolation thing without allowing the engine to jump around wildly

yes i do believe that vibration can be an issue, in all engines, but i don't believe that a properly balanced engine will exhibit destructive forces no matter how it is mounted.

"And, what if your engine does have a flaw?"

then it will eventually break no matter how it is mounted.


as far as bending forces, if the engine is properly engineered it will handle all these forces internally,

there are very few places within a properly designed engine that exhibit bending forces, rocker arms, the crankshaft, wrist pin being a few
the rockers can and are built heavy enough to last forever
the wrist pin is built large enough to handle the stress without bending
the crankshaft, is sufficiently large in journal diameter to handle the modest power densities

concrete bases have no effect on rocker life, or wrist pin life.

resilient mounts absorb motion, over a range of motion and in doing so slow it down and then return it over an equally slower motion,this effectively absorbs and dissapates as heat much of the energy in the motion/vibration,  as opposed to concrete which being like an anvil returns this motion/shock nearly immediately and with an equal and opposite force and in some instances with an amplification of this force/vibration.

a concrete block is a muffler, a blindfold, a pacifier, it basically masks these forces, it does not absorb them

take your piece of glass and your hammer

hold a concrete block against the glass and strikeit with your hammer, and watch your glass break
now hold a rubber block against your glass and hit the rubber with the hammer,

alternatively, take a piece of strap iron, an anvil and a hammer, beat on the strap iron while it lays on the anvil and you will see it distort readily
now put the strap on a block of wood or hard rubber, and beat on it,,, you will beat yourself silly before you deform it nearly as bad as the anvil
why is this? because the anvil returns the work instantly back to the hammer
why does the hard rubber not work as well? because it absorbs and returns little of the energy of the hammer

now substitute soft metal rod and main brgs for the strap of steel and see what happens

another visual method is the swinging balls, you know the ones, you swing one down and it hits the 5 hanging, the energy from the first is transmitted thru to the last and is returned back thru to the first, if you insert a bit of rubber into the stationary balls the action stops, the energy has been absorbed.

so what does this have to do with the crankshaft you might ask?

the ignition point directs a stress to the crank (diesel knock) this is a relatively fast event, this sharp knock is sent into the mount and returned with the same frequency and intensity if mounted on a concrete base, if mounted on a resilient base this action is not only slowed down but the reaction as well, along with the intensity because of dissapation.

bob g

[Procrustes]

i am not saying that mounting to concrete is better than any other mount, just as i am not saying that mounting to something else is better than concrete, although
i can make the case that concrete returns and in some cases amplifies the shocks, vibration and stresses imparted upon it back to the engine.

I'll read with interest if you do make this case.

also please note, that even if bolted to a concrete block it is still on a resilient mount albeit a very stiff resilient mount, (unless you cast you crete ontop of a granite bedrock)

you seem to take to the tangent and extremes to support your position

i don't support spring mounting the engine or any engine, and don't know anyone that would
there is such a thing as an engineered resilient mount, that does the isolation thing without allowing the engine to jump around wildly

yes i do believe that vibration can be an issue, in all engines, but i don't believe that a properly balanced engine will exhibit destructive forces no matter how it is mounted.

"And, what if your engine does have a flaw?"

then it will eventually break no matter how it is mounted.

Perhaps the block can extend this beyond service life though.   Of course that's an advantage.

as far as bending forces, if the engine is properly engineered it will handle all these forces internally,

there are very few places within a properly designed engine that exhibit bending forces, rocker arms, the crankshaft, wrist pin being a few
the rockers can and are built heavy enough to last forever
the wrist pin is built large enough to handle the stress without bending
the crankshaft, is sufficiently large in journal diameter to handle the modest power densities

concrete bases have no effect on rocker life, or wrist pin life.

resilient mounts absorb motion, over a range of motion and in doing so slow it down and then return it over an equally slower motion,this effectively absorbs and dissapates as heat much of the energy in the motion/vibration,  as opposed to concrete which being like an anvil returns this motion/shock nearly immediately and with an equal and opposite force and in some instances with an amplification of this force/vibration.

a concrete block is a muffler, a blindfold, a pacifier, it basically masks these forces, it does not absorb them

take your piece of glass and your hammer

hold a concrete block against the glass and strikeit with your hammer, and watch your glass break
now hold a rubber block against your glass and hit the rubber with the hammer,

You don't seem to understand the argument.  The analogy would be, tap the bottle on a block of concrete vs. tap the bottle oscillating on a flexible mount.  The latter is more dangerous.

alternatively, take a piece of strap iron, an anvil and a hammer, beat on the strap iron while it lays on the anvil and you will see it distort readily
now put the strap on a block of wood or hard rubber, and beat on it,,, you will beat yourself silly before you deform it nearly as bad as the anvil
why is this? because the anvil returns the work instantly back to the hammer
why does the hard rubber not work as well? because it absorbs and returns little of the energy of the hammer

Same as above.

now substitute soft metal rod and main brgs for the strap of steel and see what happens

another visual method is the swinging balls, you know the ones, you swing one down and it hits the 5 hanging, the energy from the first is transmitted thru to the last and is returned back thru to the first, if you insert a bit of rubber into the stationary balls the action stops, the energy has been absorbed.

so what does this have to do with the crankshaft you might ask?

the ignition point directs a stress to the crank (diesel knock) this is a relatively fast event, this sharp knock is sent into the mount and returned with the same frequency and intensity if mounted on a concrete base, if mounted on a resilient base this action is not only slowed down but the reaction as well, along with the intensity because of dissapation.

bob g

[hotater]

Does a shivering horse still put full power to the plow?

[Procrustes]

Does a shivering horse still put full power to the plow?

Sure.

We are all agreed, I think, that CS's are bound to vibrate, and that vibration can limit the service life of an engine, and that flexible mounts allow the engine to move some.  If you further accept that the engine will move acyclically, and that larger stresses place non-linear damage to metals, then I believe you must also accept that flexible mounts are inferior.

I'm trying to see how your analogy applies to this, but it escapes me.  I'd appreciate an elaboration.

[hotater]

Sorry to be so obscure, but my OBSERVATION is that a Mini-Petter pumps MORE water when the engine is stabalized by a heavy concrete mount.

The horse analogy is this--  If a horse equals one HP but it takes half a HP just to stand up, move and create the energy it takes to stay alive then under ideal circumstances he horse 'uses' a half horsepower to live and half a HP to pull the plow.  If the horse is cold and shivering that activity uses a portion of the available HP to the plow, right?.

If the engine is creating motion through 'burning' of fuel and part of that motion goes to making the engine shake and jump and vibrate isn't there less energy *output* to the work being done?

I can SHOW this in actual water being pumped by doing nothing more than loosening four tie down bolts.

Yes, it *could* be that the vibration affects the effeciency of the pump through cavitation of air entrainment or changing of geometry within the pump, but the bottom line is MORE water with a stable pump.

[Procrustes]

You reknowned gunsmiths have to be careful, we're apt to look too deeply into what you're saying.

I thought you meant shivering from pulling a load, not from cold.

I hadn't considered efficiency.  No doubt some of your mini-petter's lost energy translates into stress.

[hotater]

  Maybe it's best to postulate this:

If the goal is to turn fuel into motion, isn't it better to use ALL the motion for your work instead of some of the power going to make the engine jump up and down?

That's MY goal...spin a generator head.  Some work is lost to heat and friction, but that's not the 'product'.  Energy to the genhead is the goal and I'd like to have every available bit of power possible go towards that goal.

[Geno]

More than a few years ago, when they started putting shocks on mountain bikes I said to some friends "what a great idea for going down hill" When I explained that the up and down motion of the bike through the shocks was a loss of forward motion I got confused looks. I'm no genius, but the voices said it was logical 
Thanks, Geno

[biobill]

  Maybe it's best to postulate this:

If the goal is to turn fuel into motion, isn't it better to use ALL the motion for your work instead of some of the power going to make the engine jump up and down?

That's MY goal...spin a generator head.  Some work is lost to heat and friction, but that's not the 'product'.  Energy to the genhead is the goal and I'd like to have every available bit of power possible go towards that goal.

  It would be interesting to see a dyno test of the same engine on a resiliant vrs rigid mount. My gut feeling is that the results would be identical. I don't believe that you are 'conserving' useful energy with a rigid mount, just absorbing waste motion in a different fashion. The relationship of the piston to the crank does not change and the bottom line is torque at the crank. The cyl. pressure is against the head, essentially part of the block, not against some point in space so why would the output be affected by movement?
                                                     Bill

[mobile_bob]

i agree with BioBill

first of all one has to consider there are resilient mounts and there are resilient mounts

one type of resilient is like that used on small box store generators, which allow the engines alot of freedom of movement
another type is one that provides some isolation without allowing much movement.

at the end of the day my bet is there would not be 1% difference in an engine mounted on either concrete or resilient mounts in fuel consumption

would be interesting to see actual test results that could be duplicated by another tester.

one should also consider much of the forces that are absorbed by the resilient mounts are returned to the engine, any energy lost in movement (most of which is returned) is converted to heat, there just isn't that much heat being generated in a resilient mount. Don't believe me, touch one some time, they may be slightly warm, but are by no means hot. yes there is some loss of btu's in the mounts, but seriously it aint much.

bob g