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General Discussion / Re: concrete vs resilient mounting round 2
« on: November 25, 2006, 07:47:49 AM »" 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?