Aasco flywheel is here.

[insite]

How many g's do you think are exerted outward by centripetal force at the edge of a flywheel turning 7300 rpm? 100? 1000?

Try ELEVEN THOUSAND THREE HUNDRED. 11,300g at my redline. That means 17grams becomes 425 lb. Over time, that wobble can absolutely fatigue the crank. It's not forged, it's sintered.

[thstone]

Originally Posted by insite

How many g's do you think are exerted outward by centripetal force at the edge of a flywheel turning 7300 rpm? 100? 1000?

Try ELEVEN THOUSAND THREE HUNDRED. 11,300g at my redline. That means 17grams becomes 425 lb. Over time, that wobble can absolutely fatigue the crank. It's not forged, it's sintered.

My point is that the crank won't fatigue because the force (your calculation of 425 lbs) is far below the fatigue load. This situation isn't like bending a paper clip back and forth until it breaks. This load level is more like me trying to bend a street light post. No matter how long I push on it (months, years, decades), it ain't never gonna break.

This is why owners can drive around with a failing DMFW for thousands of miles (which produces 100x the force of your example LWFW) and everything is still ok.

[insite]

Originally Posted by thstone

My point is that the crank won't fatigue because the force (your calculation of 425 lbs) is far below the fatigue load. This situation isn't like bending a paper clip back and forth until it breaks. This load level is more like me trying to bend a street light post. No matter how long I push on it (months, years, decades), it ain't never gonna break.

This is why owners can drive around with a failing DMFW for thousands of miles (which produces 100x the force of your example LWFW) and everything is still ok.

Sorry, you have no idea what you are talking about

[Cloudsurfer]

Originally Posted by insite

Sorry, you have no idea what you are talking about

Totally Agree.

[thstone]

Originally Posted by insite

Sorry, you have no idea what you are talking about

Ok, I'll agree and maybe I have it all wrong. Can you please enrich my understanding:

If I recall correctly, most metals have a stress below which they can withstand an infinite number of stress cycles (me pushing on a light post). Above this level, the life disminishes in proportion to the stress and number of stress cycles.

So, the question is: How does the load you calculated (425 lbs) compare to the fatigue stress of sintered steel?

[insite]

you're thinking about this the wrong way. earlier, you said that harmonics were a red herring. they are not; there are force multipliers to consider that make that 425lb load increase by MANY multiples.

one is simple leverage; the flywheel actually sits several inches away from the first bearing inside the case. you have the flywheel flange, some seal surface, some chain sprockets, a little more dead space, and FINALLY a bearing. the 425lb bending moment is actually multiplied several-fold at the point of the first main bearing.

second: harmonics.

consider this: are the pressure waves from my voice strong enough to break a glass? hell no. i can yell at a glass all day long and nothing will happen. however, if ella fitzgerald hits the natural frequency of that glass, it will shatter in a hurry. it's not the force of her voice that does it; it's the fact that she puts the glass into an excited harmonic state that eventually causes enough amplitude to fracture the glass.

if you ever did the glass breaking experiment in physics, you noticed a few things:

1. it WORKS
2. you have to turn up the sound a little bit; if it's too quiet, it doesn't work
3. when you get it loud enough, the glass breaks almost IMMEDIATELY

so to get an object into an excited harmonic state, you need two things:

1. the proper frequency
2. AMPLITUDE: you need enough initial force per cycle to start the runaway harmonic exitation



now on to the engine. there are several forces occuring at once. let's simplify and break them into three planes and a twisting moment:

x plane is axial: along the crankshaft and level with the ground
y plane is axial: along the crankshaft and perpendicular to the ground
z plane is radial: like the flywheel
twisting moment obviously twists the crankshaft


i'm breaking this into multiple posts......post 1 complete.

[insite]

ok, continue. now let's consider our three planes.

in the x plane our pistons are moving. we have a flat-6 motor with three pistons on each side. normally with an inline 3, we'd have a rocking couple as a result of the firing order & odd number of cylinders (the forces would attempt to 'rock' the crank fore & aft). this is precisely balanced by the other bank of cylinders, so a flat 6 is a very well balanced engine to begin with. as a result, heavy counterweights are not necessary.

as for the y plane? since there are no counterweights, things are pretty stable.

combine these factors along with the fact that we have seven main bearings, & things are looking nicely balanced & rigid insofar as the engine configuration is concerned.

now we get into torque. every time a piston fires, it pushes down on a rod journal. this force actually deflects (bends) the crankshaft a little bit, & the crank snaps back. this occurs at the natural frequency of the crankshaft. since the crankshaft is only spinning one way, it isn't possible to counterbalance this force. (FYI, some engines use balance shafts, but they only serve to reduce vibration, NOT do un-do this twisting moment). in engines where the natural frequency of the crankshaft is similar to the frequency of the 1st, 2nd or 3rd order harmonic created at any engine speed between idle and redline, a harmonic balancer is used. it is tuned to the natural frequency of the crank, and the elastomer core of the balancer is designed to absorb this frequency. this prevents an 'excited harmonic state' from occuring at the NF of the crank.

part 2 done, more to come.....

[insite]

continuing....

it is my personal belief that the M96 doesn't really have issues with torsional harmonics. a lot of people make the case that the dual mass flywheel & its elastomer serve as a harmonic balancer. i don't think they really do. in general, torsional harmonics go out of control at the FRONT of the motor because the driveline serves to damp the other end. i think the DMF was designed to reduce driveline noise. this becomes readily apparent when you swap in a single mass LWFW. even with a sprung clutch, the 5-speed gearbox is NOISY without the DMF. if porsche was worried about torsional harmonics, they would have added a harmonic balancer to the front of the crank.

more in a bit.

[Jake Raby]

What is illustrated here is a lot of imbalance, but it is what we see on a daily basis. For some reason no one wants to listen to our experiences, including the manufacturers of the imbalances components.

What is clear in the experience of insure is the fact that these assemblies require balancing before installation. This something we have known for a decade, but something that no one seems to concur with.

I gave up trying to share, we just apply our experiences to those who seek out our specialized services. Glad to see the engine is smooth now, at least we were effective.

[Iflylow]

Sounds like this one has been goin' for a while, and it's all over but the cryin'.

In aviation, we take harmonics very seriously, and I am constantly amazed at the fatigue which is caused by seemingly unrelated components. As a very graphic demonstration on harmonic resonance, go to youtube and search "helicopter resonance CH-47" (I'm trying to avoid any copyright problems by not posting a link)

If you aren't already convinced of the dangeers, you will be after watching this. If I remember correctly, This was caused by one blade which was out of balance with the rest.

[Iflylow]

BTW, Jake,
You get a lot of flame whenever you post ANYTHING! I appreciate anyone who takes the time to share information. I was new to Boxer engines, and spent hours reading your old posts. Last weekend, I changed clutch, flywheel, RMS, IMS bearing, water pump and thermostat myself. all the information I found on this site gave me the confidence.

Thanks from all the other lurkers who don't feel the need to shoot you down.

[Jake Raby]

Being a former CH 46E Crewchief I know all about harmonics and IPS.

As far as catching heat:
Anytime that anyone is in a position of authority within a group there are those who feel inlined to go out of their way to pick the person apart. Thats just life and in my world it doesn't matter. I learned years ago that at least 10% of the population can't be pleased and the majority of that percentage is the most vocal online. The tables turn when we are eyeball to eyeball and they are given the opportunity to take a stab.

I expect this to only get worse after my book is published as it includes a ton of info that defies conventional wisdom, because it is written directly from experience. The peoplewho appreciate what we create and share make it worth all the BS that the sharing creates.

The moral of this story is to never assume that the components that are removed from a box are balanced to a tight enough tolerance for direct install onto an engine.. Then never assume that these components will match well enough with associated components to allow for direct installation. Insite's flywheel was out of balance and so was his pressure plate, coupled together they created severe imbalance, even after being mated with 5 different position indexes before being corrected. Thanks to insite for being kind enough to post his experience, which helped me illustrate my thoughts on this topic once and for all.

I stay away from these flywheels and haven't installed one in over 2 years. It's clear that the only way for me to be pleased with a LWFW option for us us to make it in house, but I have more more important fish to fry with the time we have.. Dual mass works fine for us, we make big enough power increases with every engine not to need a LWFW to impress the driver.