its been said of me by a close friend "bob you are like a dog on a bone"
i keep telling myself that i won't get back into this discussion but i just can't seem to help myself
so here goes
1. it has been stated by those that know listers, "a 5/1 is the same engine as a 6/1"
2. the lister engineers originally spec'd a concrete block for the 5/1 to be approx 605 lbs
3. later in production the spec changed to nearly a ton
following logic, if both the 5/1 and the 6/1 are the same engine, then why the disparity in the weight of the concrete block?
A. the earlier lister engineers got it wrong?
B. the later lister engineers got it right?
C.the earlier production engine's were balanced better than the later production engine's?
D. empirical evidence based on listers experience with folks installing these engines on everything from granite bedrock
to swamp land dictated a revision of the earlier spec?
some time ago i presented the formula used to spec the concrete block for a 5/1, no one refuted the formula
it was based on geometry of the engine and basic vector physic's
no such formula works for the later spec of nearly a ton of crete, at least none i have been able to find, compute, or calculate.
moving on
nobby presented the old school text pertaining to concrete foundations, the use of cork, the use of springs and the combination
of both that was state of the art back in the day,, good stuff for what was available back then.
what was interesting was the placement of the spring mounts as it relates to the crankshaft centerline, this point cannot be understated
in my opinion.
in any successful mounting system the underlieing goal should be to keep the crankshaft in a stable plane, it can be allowed to move up and down (as long as it stays in a level plane) or from side to side (staying in the same horizontal plane) without imparting undue stresses on the crank (within reason of course). what we don't want is the crank to cant off level in either plane. it really doesn't present undue stresses to any other part of the engine if all other movement is centered on the crankshaft centerline. Basically let her rock and roll a bit as long as the crankshaft is kept at the center of this rocking moment, kept level in both planes. (again within reason)
now we can be certain that the crankshaft will stay level in all planes if we mount it to enough mass (ton of crete), but
we have issues with transmission of noise.
in my opinion and it can be demonstrated easily this transmission of noise/sound is typically blamed on balance issues (in some cases
this obviously is the prevalent cause), but it is not typically the cause of the offending transmitted vibration. what is transmitted is the
combustion event. if you put your ear to a concrete floor and have someone hit the floor many feet away with a hammer you will hear the
hammer blow, even though there is no balance issues,, you hear the impact. this impact is the combustion event or pressure spike when the diesel ignites. my bet is if you sat a metal can on the floor and put an m80 in it and set it off you would hear it in the floor several 10's of feet if not more.
so the bottom line comes down to a simple question "how do we isolate the combustion event, and keep the crankshaft stable?"
the answer to that question is with the proper design of the engine mounting system and some from of resilient mounts,
certainly a ton of concrete isolated with cork on the bottom and sides will do the job, but
not everyone want's or can install that much concrete, maybe he is a renter? maybe he wants to move and not have a huge concrete block
to explain to a new owner? maybe he is unsure of the soil conditions in his location and fears the outcome might not be acceptable?
so what does that leave those individuals with?
the answer to that one is, a specifically engineered mounting system that is resiliently mounted.
luckily the listeroid being designed to run on a concrete block and do so forever it seems is built heavily so that it can survive forever on concrete, this heavy design presents no weak points that would preclude the use of a properly engineered/designed mounting system using modern resilient mounts, so long as the focal point is the crankshaft and making certain it remains in a stable plane and isn't allowed to cant end for end. canting end for end places stresses on the crankshaft due to the gyro effects of the flywheels, it is possible under the right circumstance to get the motion in a range where destructive resonance might occur which likely will stress the main brgs, maybe stress and crack the crankshaft or worse. there likely is a critical speed where this would be a problem,, i sure would not want that critical speed to be anywhere around the rpm that the engine is set to run under load at.
a well designed mounting system need not be horribly complex, the job gets easier the wider the mounting spaceing is, and much more difficult the narrower it is. this primarily is the reason that i cringe when i see rubber mounts placed right under the crankcase with the mouting bolts going through them. the stresses are immense when the spacing is so narrow and therefore the engineering of the mounts gets much more complex and important. widely spaced mounts reduce these stresses to very managable levels.
using a cradle mount with the crankshaft centerline used as the mount plane, spaced apart a reasonable distance affords the use of off the shelf resilient mounts (with a little math) or off the shelf adjustable spring and rubber mounts (with almost no math) where you can simply
dial in what is needed after the assembly is put under load and monitored.
i see no reason that any single cylinder diesel cannot be resiliently mounted using such a method (cradle with the crankshaft centerline)
and have an engine that while it appears to wiggle about will have the crankshaft running nearly dead true at speed and under load.
this is not to say that the crankshaft won't move about when the engine coast down because it will pass through a critical speed on coast down and on starting (likely somewhere around 250rpm on a 6/1), but it will pass through that range quickly and present no problems.
now the twins might be another matter entirely, this is where wider spacing of the mounts would be very helpful in my opinion.
lastly there is nothing wrong with a ton of concrete, it works and works well as a mounting system, however
it just isn't the last word on engine mounting as some would suggest and clearly is not a good option for some of us
that cannot tolerate vibrations being transmitted to other living spaces.
anyway that is my story and i am stickin with it
bob g
